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最終報告書

平成２４年 3月

日本船舶海洋工学会

摩擦抵抗低減研究委員会

まえがき日本船舶海洋工学会摩擦抵抗低減研究委員会

委員長大阪大学戸田保幸

摩擦抵抗低減研究委員会（略称Ｓ７委員会）は、26 期国際試験水槽会議（ITTC）に設置され

表面処理に関する専門家委員会（Specialist Committee on Surface Treatment、以下 ITTC 委

員会）の活動に対応する委員会として、日本船舶海洋工学会に設置されたストラテジー委員会で、

平成 21 年度より 3 年間活動してきました。目的は「摩擦抵抗低減法に関しての実船性能推定手

法など、今後利用される可能性のあるペイント・空気潤滑などによる摩擦抵抗低減技術、および

模型試験等に基づく摩擦抵抗推定法に関する共同研究を実施すること」としておりましたが、共

同研究は行わず、これまでの研究をまとめて、新しい塗膜などに対してどのような推定法を作れ

ばよいのかなどを討議してきました。本委員会では、ITTC 委員会の日本からの委員をサポートするのが大きな目的であることから、

表面処理による摩擦抵抗等を推定、低減する技術に関する文献調査及び表面処理による摩擦抵抗

等を推定、低減する技術に関するレビューと理論的検討を行った。前者については昨年約 80 編

の文献について、その概要を英和両文で１編あたり１ページの体裁で要約集としてとりまとめ、

「塗膜、汚損等の表面摩擦抵抗に関する文献調査集」を印刷、製本し配布しました。後者につい

ての各委員からの発表資料を取りまとめたものが今回の最終報告書です。後者の活動を紹介いたしますと委員会は摩擦抵抗に対して大きな低減効果がある空気潤滑法

等は取り扱わず、ITTC 委員会との関連から主に塗膜面の摩擦抵抗を調査しました。ただし摩擦

抵抗変化により伴流係数が変化するなどは共通のことであるのでこの委員会でも検討すること

になりました。内容は塗膜面の試験法としてどのようなものがあるかを調査し、回転円筒を用い

た計測、パイプによる計測、平板による試験、数式船型を用いた曳航試験など試験可能なレイノ

ルズ数範囲とこれらの試験で得られた結果から高いレイノルズ数の実船相当の抵抗を推定する

方法を調査検討してきました。その中には最近開発された海上技術安全研究所の高精度な平行平

板を用いた手法も紹介されました。また表面の性質（たとえば幾何学的な粗度と流体力学的に考

察しやすい等価な砂粗度など）が分かったとしてそれをどのように使っての実船の性能推定等に

ついても検討しました。また粘性抵抗変化によりプロペラ面平均流速推定法も変える必要がある

こと、相関としてのΔCF と表面状況によるものの分離などが話し合われています。しかしなか

なか一致した方法が提案できる状況までは至っておりませんが、いくつかの考え方が資料で示さ

れています。またこの委員会のあと共同研究を行うプロジェクト委員会についても話し合いがも

たれましたが、全機関が参加できるものはなかなか難しいという結論となりました。たとえば粗

度に関するデータベースを作るという提案に対しても各機関計測は行いたいが、公表してデータ

を共有することには参加しにくいというものなどどうしても集まっていただいたすべての機関

がデータを共有するようなプロジェクトは難しく、実船のさまざまな計測手法などであれば共同

開発可能であろうかということで新しいプロジェクト研究委員会の提案を行わないまま、ストラ

テジー研究員会（S７委員会）の活動を終わることになりました。研究活動としては半ばという

感じですがこの資料集が今後のこの分野の研究を行う方々への一助となれば幸いです。これまで活動としては、下記の表に示すように 3 年間で 10 回の会合を持ち、各委員からの資

料に対して検討を行ってまいりました。この報告書にのせたもの以外にも各委員から発表がなさ

1

れましたが、一部は図のみであったりしたため省略させていただきました。また造船各社からの

委員には、実船摩擦抵抗推定に関し多くの有益な意見をいただきました。最後に委員名簿と、こ

れまでオブザーバーとして討論に参加していただいた方々の名簿を示します。委員会開催履歴

第 1回 2009/06/09 広島大学学士会館 8 名

第 2回 2009/11/14 大阪大学大学院工学研究科船舶海洋部門 10 名

第 3回 2010/01/21 日本船舶海洋工学会事務局会議室 10 名







第 10 回 2011/12/09 日本船舶海洋工学会事務局会議室 10 名

委員およびオブザーバー

委員長戸田保幸（大阪大学大学院）委員川村隆文（東京大学）

委員甲斐寿（横浜国立大学大学院）委員藪下和樹（防衛大学校）委員勝井辰博（神戸大学）委員土岐直二（愛媛大学）委員日夏宗彦（海上技術安全研究所）委員川島英幹（海上技術安全研究所）委員木村校優（三井造船昭島研究所）委員村上恭ニ（住友重機械マリンエンジニアリング）委員長屋茂樹（ＩＨＩ技術研究所）委員川北千春（三菱重工業）委員（事務局）田中寿夫（ユニバーサル造船）委員代理池田剛大（三井造船昭島研究所）

オブザーバー山盛直樹（日本ペイントマリン）オブザーバー肥後清彰（日本ペイントマリン）オブザーバー高井章（日本ペイントマリン）オブザーバー柳田徹郎（MTI）オブザーバー安藤英幸（MTI）

2

次ページ以降は各委員による発表をまとめたものである。配布資料として配布されたもの、

発表用パワーポイントファイルを印刷したもの、発表資料から少し文章をつけたものなど

さまざまな形があるが、再度形式をそろえて書き直す時間も考えてそのままの形で収録す

ることとした。それぞれの委員ごとにまとめている。内容も計測法について過去の研究を

レビューしたもの、過去に委員の機関が行ったものなどさまざまである。また ITTC 委員会

対応の委員会であったので、ブラジルで 2011 年 9 月に開催された総会でのレポートと関連

のグループディスカッションでの発表も資料をいただき収録している。簡単な目次は以下

のとおりである。

川村委員 4

川村「実船スケールレイノルズ数の CFD について」 5

川村、柳田「プロペラ性能に対する表面粗さの影響の CFD による推定」 17

田中委員 25

田中「粗度高さ定義比較」 26

田中「管内流を利用した摩擦抵抗の計測」 27

田中「回転円筒を用いた摩擦抵抗の計測」 32

勝井委員 46

勝井「粗度影響を考慮した平板摩擦抵抗の算定について」 47

勝井,泉「等価砂粗度による平板摩擦抵抗係数の増加量-計算結果の表示について」 52

勝井「後流関数を考慮した平板摩擦の粗度影響について」 54

日夏、川島委員 57

NMRI 流体設計系「平行平板曳航法による平板の摩擦抵抗評価」 58

日夏、川島「摩擦応力計測法について」 72

戸田委員 87

資料１ Hoang, Toda, Sanada ISOPE2009 論文 88

資料 2 Yamamori, Toda, Yano ISME2009 論文 94

資料 3 戸田、眞田、植原摩擦抵抗低減に関する考察 100

資料 4 塗膜模型船を用いた水槽実験 111

資料 5 深江丸の推力、トルク計測 118

資料 6 ITTC 表面処理委員会レポート 121

資料７ ITTC グループ討議 Green Ship Atlar 教授資料 152

資料 8 山盛氏による防汚塗料についての解説資料 157

3

川村委員の発表資料

川村「実船スケールレイノルズ数の CFD について」では高レイノルズ数まで CFD コード

で計算した例をもとに様々な説明がなされた。

川村、柳田「プロペラ性能に対する表面粗さの影響の CFD による推定」では表面粗度の影

響を考慮した CFD 計算を行い、性能の変化を示して ITTC1978 の式との比較を行った例が

説明された。

4

CFD

•

•

•

5

•1. Y. Tahara, T. Katsui, Y. Himeno: Computation of Ship Viscous

Flow at Full Scale Reynolds Number, Journal of The society of Naval Architects of Japan,Vol.192,2002,pp.89-101

2.(4), 305-308,

20073.

(10), 29-36, 20094.

222010

•

•

••

6

Y. Tahara, T. Katsui, Y. Himeno (1)

• 2-Layer k-� Wall-function k-�Series 60

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7


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(2)

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12

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15

CFD (1)• k-wCf y+

CFD (2)•Re=1e9 Cf0=0.0015Lpp=1 y+=0.1 �y=3.6e-9

•1+K

16

MTI

••

•

•

•

• CFD

17

• Wan et al., The Experiment and Numerical Calculation of Propeller Performance with Surface Roughness Effects,

(238), 49-54, 2002•

:(239), 55-60, 2003

–––

•(10), 29-36,

2009–

CFD

•

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• k-w-SST

•

18

POT

0

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19

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s ��

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20

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0

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ITTC1978ITTC1978

DT CDP

DCZK �� 3.0

DQ CDCZK �� 25.0

�CD 1.05

fT CK �� 5.6

fQ CK �� 58.0

QT KK �� 26.1

QT KK �� 2.11ITTC1978

22

ITTC1978ITTC1978

DT CDP

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DQ CDCZK �� 25.0

fT CDP

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ITTC1978

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23

• CFD

• (�Cf) KT KQ (�KT,�KQ)

• �KT �KQ• ITTC1978 �KT

• �Cf �Cf�KT �KQ

24

田中委員の発表資料

田中「粗度高さ定義比較」では様々な粗度の定義（計測器も含めて）があるが、同じ粗度

高さであっても、どの定義を使っているか認識することが必要との話がなされた。

田中「管内流を利用した摩擦抵抗の計測」では、これまでのパイプを使った研究がレビュ

ーされた。チャンネル流れでの計測との比較もなされた。

田中「回転円筒を用いた摩擦抵抗の計測」ではこれまで田中委員により行われた回転円筒

試験装置による試験が説明された。

25

2010/04/16

粗度高さ定義の比較ユニバーサル造船田中

26

1

ユニバーサル造船ユニバーサル造船田中寿夫田中寿夫

管内流を利用した摩擦抵抗の計測管内流を利用した摩擦抵抗の計測

2

直線円管を用いた摩擦抵抗計測：概要直線円管を用いた摩擦抵抗計測：概要

•• 山崎・小野木・仲渡・姫野・田中・鈴木：「表面粗山崎・小野木・仲渡・姫野・田中・鈴木：「表面粗度による抵抗増加の研究（第１報告）、日本造度による抵抗増加の研究（第１報告）、日本造船学会論文集１５３号、１９８３船学会論文集１５３号、１９８３

•• 小野木・山崎・仲渡・姫野・田中・鈴木：「表面粗小野木・山崎・仲渡・姫野・田中・鈴木：「表面粗度による抵抗増加の研究（第１報告）、日本造度による抵抗増加の研究（第１報告）、日本造船学会論文集１５５号、１９８４船学会論文集１５５号、１９８４

•• 直線円管における圧力損失を計測することによ直線円管における圧力損失を計測することにより、円管内面の摩擦抵抗を計測り、円管内面の摩擦抵抗を計測

•• 円管内面の粗度あるいは塗装状態が摩擦抵抗円管内面の粗度あるいは塗装状態が摩擦抵抗に及ぼす影響を明らかにすることが目的に及ぼす影響を明らかにすることが目的

27

3

直線円管を用いた摩擦抵抗計測：抵抗の計測方法直線円管を用いた摩擦抵抗計測：抵抗の計測方法

• 内径50mm・全長4,000mmの直線円管を使用

• 側壁に設けた静圧孔を用いて管路の圧力損失を計測し、これをDarcyの摩擦抵抗係数に換算

• 静圧孔から総圧管を挿入して円管断面内の流速分布も計測

4

直線円管を用いた摩擦抵抗計測：粗度の計測方法直線円管を用いた摩擦抵抗計測：粗度の計測方法

• 円管内側に研磨用砂を接着して砂粗度を模擬

• 円管内側の粗度を計測する代わりに、同様の方法で作成した粗度平板について、ＢＳＲＡ式可搬型粗度計で表面粗度を計測

• ＢＳＲＡ粗度は、タングステン球を対象面に接触させ、面に沿って100mm移動させたときの最大粗度を示す

28

5

直線円管を用いた摩擦抵抗計測：管内の速度分布直線円管を用いた摩擦抵抗計測：管内の速度分布

• 総圧管を断面内でトラバースさせて、速度分布を計測

• 管直径の40倍程度の助走区間をとっているため、計測部では安定した速度分布が得られている

6

直線円管を用いた摩擦抵抗計測：滑面の摩擦抵抗直線円管を用いた摩擦抵抗計測：滑面の摩擦抵抗

• 圧力損失から求めた管摩擦抵抗係数ｆをPrandtlの実験式と比較

• 広範囲のReynolds数にわたって、実験値とよく一致

• ばらつきも少ない

29

7

直線円管を用いた摩擦抵抗計測：粗面の摩擦抵抗直線円管を用いた摩擦抵抗計測：粗面の摩擦抵抗

• ほとんどの供試粗面円管はReynolds数によらず一定値の摩擦抵抗となっている→流体力学的に完全粗面の状態

• 管摩擦抵抗係数ｆはReynilds数に依存せず,Nikuradseの砂粗度ks/Dの関数となっている

8

直線円管を用いた摩擦抵抗計測：粗度の影響直線円管を用いた摩擦抵抗計測：粗度の影響

Pipe No. ｆＫｓ／ＤＫｓ（μｍ）

ＫＢＳＲＡ（μｍ）

Ｋｓ／ｋＢＳＲＡ

２０．０１８０．０００７３６６４０．４９

３０．０２８０．００３８１９６１３０１．５１

４０．０３１０．００５４２６６２０２１．３２

５０．０４４０．０１５１７７８５３８１．４５

６０．０５９０．０３２４１６８５１１３２１．４６

30

9

直線円管を用いた摩擦抵抗計測：粗度の影響直線円管を用いた摩擦抵抗計測：粗度の影響

• 計測された摩擦抵抗係数から求めたNikuradseの砂粗度ｋｓと、BSRAの粗度は比例関係にある

• 粗度が小さい場合は、必ずしも比例にはならない

• 新造船の場合の粗度は高々５０～１５０μｍ程度であり、比例関係が当てはまるとは言い切れない

10

溶接ビードが摩擦抵抗に及ぼす影響溶接ビードが摩擦抵抗に及ぼす影響・「白勢：粗面と溶接ビードによる船の抵抗増加（西部造船会報・「白勢：粗面と溶接ビードによる船の抵抗増加（西部造船会報7575号）」号）」

・Ｌ・Ｌpp=225mpp=225mの船体がの船体が1010ブロックからなると仮定ブロックからなると仮定

・溶接ビードは幅・溶接ビードは幅20mm20mm・高さ・高さ5mm5mmと仮定と仮定

・摩擦抵抗に及ぼす影響は２％程度⇒粗度の・摩擦抵抗に及ぼす影響は２％程度⇒粗度の1/101/10オーダーオーダー

5mm

31

ユニバーサル造船ユニバーサル造船田中寿夫田中寿夫

Ｓ７委員会＃６Ｓ７委員会＃６

回転円筒を用いた回転円筒を用いた摩擦抵抗の計測摩擦抵抗の計測

回転円筒試験装置（外観）回転円筒試験装置（外観）

外円筒（固定）

トルク計

モーター

32

回転円筒試験装置（内部）回転円筒試験装置（内部）

回転軸

供試円筒（側面を塗装）

エンドプレート（２次流れを抑制）

実船における摩擦抵抗推定法実船における摩擦抵抗推定法

1.1. 回転円筒－固定円筒管に生じる境界層内にお回転円筒－固定円筒管に生じる境界層内における速度分布に壁法則を仮定ける速度分布に壁法則を仮定

2.2. 壁法則から円筒表面に作用する平均摩擦応力壁法則から円筒表面に作用する平均摩擦応力を推定を推定

3.3. 回転円筒試験で得られた摩擦抵抗係数に一致回転円筒試験で得られた摩擦抵抗係数に一致するように壁法則で等価砂粗度Ｋｅを決定するように壁法則で等価砂粗度Ｋｅを決定

4.4. 得られた等価砂粗度によって実船尺度におけ得られた等価砂粗度によって実船尺度における摩擦抵抗の増減量を評価る摩擦抵抗の増減量を評価

33

流速分布の比較流速分布の比較－人工粗度円筒の場合－－人工粗度円筒の場合－

••境界層内速度分境界層内速度分布に壁法則を仮定布に壁法則を仮定

••表面粗度の異なる表面粗度の異なる円筒の実験値と比円筒の実験値と比較較

••等価砂粗度Ｋｅを等価砂粗度Ｋｅを仮定して求めた速仮定して求めた速度分布は実験結度分布は実験結果と定量的に良好果と定量的に良好な一致を示すな一致を示す

1 1.5 2 2.5 30

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

2r/D

u/U

Estimated (Bout=500m)Ks= 0mKs= 34mKs=121m

MeasuredRF1(Rz= 6.2m)RF3(Rz= 16.6m)RF5(Rz=100.5m)

平均摩擦応力の比較平均摩擦応力の比較－人工粗度円筒の場合－－人工粗度円筒の場合－

••流速分布から流速分布から決定した等価決定した等価砂粗度Ｋｅを用砂粗度Ｋｅを用いて供試円筒いて供試円筒に作用する平に作用する平均摩擦応力を均摩擦応力を推定推定

••レイノルズ数のレイノルズ数の変化が摩擦応変化が摩擦応力に及ぼす影力に及ぼす影響はよく推定さ響はよく推定されているれている

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036

Rn

Ct

Estimated (Log law×1.96)Ks= 0mKs= 34mKs=121m

MeasuredRF1(Rz= 6.2m)RF3(Rz= 16.6m)RF5(Rz=100.5m)

34

塗膜面の表面状態変化を塗膜面の表面状態変化を考慮した摩擦抵抗の計測法考慮した摩擦抵抗の計測法

１）供試塗膜を側面に塗装した円筒を作製１）供試塗膜を側面に塗装した円筒を作製

２）試験装置で回転数２）試験装置で回転数00～～700rpm700rpmの範囲で回の範囲で回転トルクを計測→摩擦抵抗係数を算出転トルクを計測→摩擦抵抗係数を算出

３）表面粗度をＪＩＳ方式で計測３）表面粗度をＪＩＳ方式で計測

４）エイジング用池で１ヶ月間連続回転（円筒４）エイジング用池で１ヶ月間連続回転（円筒表面における回転速度が４．５ノット相表面における回転速度が４．５ノット相当）当）

５）２）～４）の過程を３ヶ月間繰り返す５）２）～４）の過程を３ヶ月間繰り返す

エイジング装置エイジング装置

新鮮な海水が常時循環するプール内で供試円筒を連続回転新鮮な海水が常時循環するプール内で供試円筒を連続回転

実船まわり流れにおける塗膜面の暴露状態を模擬実船まわり流れにおける塗膜面の暴露状態を模擬

35

供試塗膜の要目供試塗膜の要目

初期粗度：ＪＩＳ方式で計測した最大値初期粗度：ＪＩＳ方式で計測した最大値

消耗度：１５ノット相当回転速度で研磨した場合の値消耗度：１５ノット相当回転速度で研磨した場合の値

No. No. 性質性質初期粗度初期粗度

((μμm)m)

消耗度消耗度

((μμm/m/年年) )

接触角接触角

((°°) )

RF1RF1 無塗装滑面（基準円筒）無塗装滑面（基準円筒） 11.911.9 －－－－

SF1SF1 自己研磨型自己研磨型 32.332.3 78.078.0 －－

SF3SF3 自己研磨型自己研磨型 45.645.6 41.041.0 －－

SF5SF5 自己研磨型自己研磨型 32.532.5 162.0162.0 －－

SF5RSF5R 自己研磨型自己研磨型 87.387.3 162.0162.0 －－

SW1SW1 撥水性アクリル系撥水性アクリル系 23.123.1 －－ 8585

SF5RSF5R 撥水性シリコン系撥水性シリコン系 24.024.0 －－ 129129

エイジングによる生物付着エイジングによる生物付着（撥水性塗膜）（撥水性塗膜）

１ヶ月経過１ヶ月経過

初期状態初期状態

エイジング過程でスライム（藻類の死骸）が付着エイジング過程でスライム（藻類の死骸）が付着

36

自己研磨型塗膜の抵抗係数自己研磨型塗膜の抵抗係数（初期状態）（初期状態）

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036

Rn

Ct

RF1

SF1

SF3

SF5

SF5R

00/09/11

初期粗度大のＳＦ５Ｒの抵抗が非常に大きい初期粗度大のＳＦ５Ｒの抵抗が非常に大きい

他の塗膜面は滑面を若干上回る程度他の塗膜面は滑面を若干上回る程度

自己研磨型塗膜の抵抗係数自己研磨型塗膜の抵抗係数（３ヶ月経過後）（３ヶ月経過後）

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036

Rn

Ct

RF1

SF1

SF3

SF5

SF5R

00/12/18

初期粗度大のＳＦ５Ｒの抵抗が大幅に低下初期粗度大のＳＦ５Ｒの抵抗が大幅に低下

他の塗膜面の抵抗は微増傾向他の塗膜面の抵抗は微増傾向

37

塗膜面摩擦抵抗の経時変化塗膜面摩擦抵抗の経時変化

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

Sep Oct Nov Dec

Ct×

1000

RF1

SF1

SF3

SF5

SF5R

SW1

SW3

平均粗度Rzの経時変化

0 100 2000

10

20

30

40

50

60

70

80

90

100

Day

Rz(m

)

SF1

SF1R

SF3

SF5

SF5R

SF5RR

5.5kt 10.1kt

38

平均粗度Rzと抵抗係数の相関

104 105

3

4

L/Rz

1000

Cf

at Rn=8,000,000

SF–1

SF–1R

SF–3

SF–5

SF–5R

SF–5RR

5.5kt 10.1kt

Estimated

平均摩擦応力の比較平均摩擦応力の比較－自己研磨型塗膜の場合－－自己研磨型塗膜の場合－

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036SF5R Series

Rn

Ct

00/09/11(87m)

00/10/10(79m)

00/11/13(74m)

00/12/18(59m)

Ke=115m

Ke= 75m

Ke=60m

Exp.(Rmax) Cal.

39

最大粗度Rzmaxと等価砂粗度Κｅの相関

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

140

160

180

200

Rzmax(m)

Ke(m

)

at Rn=8,000,000

SF–1SF–1RSF–3SF–5SF–5RSF–5RR

5.5kt 10.1kt

ΔΔＣＦとレイノルズ数の関係ＣＦとレイノルズ数の関係

Ｗｈｉｔｅの式を用いて等価砂粗度ＫｅからＷｈｉｔｅの式を用いて等価砂粗度ＫｅからΔΔＣＦを推定ＣＦを推定

相対粗度高さ一定の場合の相対粗度高さ一定の場合のΔΔＣＦの変化を表示ＣＦの変化を表示

106 107 108 109 10100

0.001

0.002

Rn

CF

Ke/L=1×10–5

Ke/L=5×10–5

Ke/L=1×10–6

Ke/L=5×10–6

Ke/L=1×10–7

40

実船における実船におけるΔΔＣＦの推定ＣＦの推定

船速１５ノット、海水温度１５℃と仮定船速１５ノット、海水温度１５℃と仮定

等価砂粗度高さを一定とした場合の等価砂粗度高さを一定とした場合のΔΔＣＦを表示ＣＦを表示

ＳＦ５Ｒの研磨によるＳＦ５Ｒの研磨によるΔΔＣＦの低下量は０．０００２程度ＣＦの低下量は０．０００２程度

100 200 3000

0.0002

0.0004

0.0006

0.0008

L(m)

CF

Ke=200m

Ke=100m

Ke=50mKe=25m

ITTC1978

撥水性塗膜の摩擦抵抗係数撥水性塗膜の摩擦抵抗係数（初期状態）（初期状態）

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036

Rn

Ct

RF1

SW1

SW3

00/09/11

41

撥水性塗膜の摩擦抵抗係数撥水性塗膜の摩擦抵抗係数（３ヶ月経過状態）（３ヶ月経過状態）

2 3 4 5 6 7 8 9 10 11 12 [10+6]0.0026

0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

0.0035

0.0036

Rn

Ct

RF1

SW1

SW3

00/12/18

生物付着による摩擦抵抗増加生物付着による摩擦抵抗増加

直径・高さとも１ｍｍの円柱状の生物（セルプラ）が１０ｃｍ角の範囲に約４０個付着

42

生物付着影響の推定例生物付着影響の推定例

1 1.1 1.2 1.3 1.4

0.3

0.4 RF1 1RF1 2RF1 3SF1（未使用、傷あり）SF5SF5RSW3

u/U

u/U

r/R

r/R1 1.1 1.2 1.3 1.4

0.3

0.4 0μ50μ100μ

(c)　計測速度分布(拡大）

(d)　計算速度分布（拡大）

1 1.5 2

0.2

0.3

0.4RF1 1RF1 2RF1 3SF1（未使用、傷あり）SF5SF5RSW3

r/R

r/R

u/U

u/U

1 1.5 2

0.2

0.3

0.40μ50μ100μ

(a)　計測速度分布

(b)　計算速度分布

••セルプラの付セルプラの付着による影響着による影響を等価砂粗度を等価砂粗度Ｋｅで評価するＫｅで評価すると１００と１００μμｍにｍに相当する相当する

トムズ効果の検証－回転円筒試験装置による計測例－

1 2 3 4 5 6 7 8 9 10 11 12 13 [10 +6]0.002

0.0025

0.003

0.0035

0.004

0.0045

0.005

Re

Ct

1st 2nd

PEO3(0ppm)

PEO3(118ppm)

PEO3(350ppm)

分子量１００万のＰＥＯ水溶液で最大１８％の抵抗低減を確認

43

トムズ効果の検証－効果の持続性－

0 10 20 30 405.9

6

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7

Time(min)

Q(N

m)

PEO3(0ppm)

PEO3(118ppm)

長時間にわたって剪断力を加えると、摩擦抵抗低減効果が消失する

↓添加物の物性が変化する？

トムズ効果の検証－物性値との関係－

0 100 200

0.001

0.0012

0.0014

せん断率(1/s)

せん

断粘

性係

数(P

a・s)

せん断率大で粘性係数小（Stress Thinning）

↓摩擦抵抗低減効果あり

せん断率大で粘性係数大↓

摩擦抵抗低減効果なし

44

まとめ－塗膜面と摩擦抵抗の関係－

•• 自己研磨型塗膜は研磨作用により表面粗度が自己研磨型塗膜は研磨作用により表面粗度が低下し初期状態より抵抗が低減する低下し初期状態より抵抗が低減する

•• 自己研磨型塗膜の抵抗が滑面の抵抗を下回る自己研磨型塗膜の抵抗が滑面の抵抗を下回ることはないことはない

•• 撥水性塗膜には摩擦抵抗低減効果は認められ撥水性塗膜には摩擦抵抗低減効果は認められないない

•• 強い撥水性があっても生物付着は生じる強い撥水性があっても生物付着は生じる

•• 回転円筒試験の結果から塗膜面の等価砂粗度回転円筒試験の結果から塗膜面の等価砂粗度を決定すれば、これを用いて実船スケールにおを決定すれば、これを用いて実船スケールにおける摩擦抵抗の増減量を推定することができるける摩擦抵抗の増減量を推定することができる

45

勝井委員の発表資料

勝井「粗度影響を考慮した平板摩擦抵抗の算定について」では勝井委員が行なっている後

流関数を考慮した摩擦抵抗計算法に粗度の影響を入れた方法が説明された。

勝井「等価砂粗度による平板摩擦抵抗係数の増加量―計算結果の表示について」では勝井

委員が行なっている後流関数を考慮した摩擦抵抗計算法に粗度の影響を入れた方法の結果

が説明された。

勝井「後流関数を考慮した平板摩擦の粗度影響について」後流関数を考慮していない阪大

の方法との比較が示された。

46

摩擦抵抗低減ストラテジ研究委員会資料平成 22年 1月 21日

粗度影響を考慮した平板摩擦抵抗の算定について

神戸大学大学院

海事科学研究科

勝井辰博

1. 平板摩擦抵抗係数 FC の算定手法

(1) 運動量積分式

二次元の圧力勾配のない平板周りの流れを考えると，運動量積分公式は以下のようになる．

fw cUdx

d

2

12==

ρτθ

(1)

θ ：運動量厚さ， wτ ：壁面せん断応力，ρ：流体の密度，U ：一様流速，

fc ：局所摩擦抵抗係数

運動量厚さの定義は

∫

−≡δ

θ0

1 dyU

u

U

u (2)

u：主流方向の流速，δ：境界層厚さ

これを 0=x すなわち平板前縁で運動量厚さθ が 0となる条件のもと積分すれば

xC

xU

dxxF

x

w

2

1

2

12 2

0 ==∫ρ

τθ (3)

FC ：平板摩擦抵抗係数

となる．つまり，運動量厚さθ を定義する乱流境界層内の速度分布が分かれば，(2)，(3)式より

平板摩擦抵抗係数 FC を算定することが可能となる．

(2) 平板の乱流境界層内速度分布

平板の乱流境界層内速度分布は Fig.1に示すような摩擦速度を用いた相似則が知られている．図

中に示したように境界層は I．粘性応力が卓越する粘性底層，II．粘性応力とレイノルズ応力が

同程度の Buffer 層，III．レイノルズ応力が卓越する対数領域から外層，の 3 領域に分類され，

それぞれの領域で速度分布は異なる．粘性底層，Buffer層の速度分布が FC に与える影響は微小

である．そこで本研究では，境界層内で，レイノルズ応力が卓越する対数領域から外層域の速

度分布を境界層内速度分布として用いた．その領域での速度分布は，Coles Lawと呼ばれ，以

下のような式で与えられる．

Coles Law

( ) ( )

⋅−=

−

Π++=

+

+

+

+

+

++++

δπ

δ

δκδ

κ

yyw

Fy

wCyu

cos1

ln1

(4)

τUuu =+ ， ντ yUy ⋅=+ ， νδδ τ ⋅=+ U ，

47


( )ρττ wU = ：摩擦速度， 41.0=κ ：カルマン定数，

ν ：動粘性係数， 0.5=C ：（平板のとき）， y：平板からの距離，

( ) ( )290exp21.162.0 ++ −−=Π δδ ：後流パラメタ，w：後流関数

ここで式中 Fは，粗度によって境界層内の速度分布が一様に減速する効果を表しており，粗面

の特性に応じて変化する．以後この Fを τUuF ∆= とし，粗度関数と呼ぶことにする．

Fig.1 Similarity law of velocity profile in turbulent boundary layer.

(3) 粗度関数

砂粗面的性質をもつ粗面の場合は摩擦速度 τU と粗度高さ k で表される粗度レイノルズ数

( )ντ kUk ⋅=+ の増加とともに粗度関数 τUu∆ が大きくなる．砂粗面の粗度関数 τUu∆ は，

White3)による実験式が与えられており，粗度レイノルズ数 +k が境界層内速度分布に与える影響

は(2-1-2-1)式のように表される．

( )+⋅+=∆ kUu 3.01ln1

/κτ (5)

この式を(4)式の Fに代入することにより，砂粗面での，粗度影響を含む平板乱流境界層内速度

分布が得られる．

(4) 平板摩擦抵抗係数を求めるための微分方程式 (4), (5)式より砂粗面の平板乱流境界層内速度分布式は(6)式のように表わされる．

( ) ( ) ( )++

++++ ⋅+−

Π++= k

ywCyu 3.01ln

1ln

1

κδκδ

κ

⋅−=

+

+

+

+

δπ

δyy

w cos1 (6)

平板乱流境界層の外端 δ=y で，流速uが一様流速U となるから

( ) ( ) ( )++

+ ⋅+−Π

++= kCU

U3.01ln

12ln

1

κκδ

δκτ

(7)

(7)式から(6)式を引けば，速度欠損は

100 101 102 1030

10

20

30

Ⅰ Ⅱ Ⅲ

Ⅰ: linear sublayer

Ⅱ: buffer layer

Ⅲ: log region and outer layer

y+

u+

48


( ) ( )

−

Π+−=

−+

++++

δκδ

δκτ

ywy

U

uU2/ln

1

(8)

となる。両辺に u/Uτを加え、さらに両辺を U/Uτで割ると

( ) ( )

−

Π+−=

+

++++

δκδ

δκττ

ywy

U

u

U

U2/ln

1

(9)

( ) ( )

−

Π+−=

+

++++

δκδ

δκ

τττ

τ

yw

U

Uy

U

U

U

U

U

u2/ln

11

(10)

すなわち速度欠損則は，無次元摩擦速度 ( )UUτσ = を用いて，

( ) ( )( )+++ −⋅Π

⋅−+=⋅ ηκ

σηκσ

σ wu 2ln1 (11)

ただし，+++ ≡ δη y

(2)式で定義される運動量厚さθ は定義式において y を y+に変数変換すれば

+⋅= uu σ ，

ντ /yUy =+(

+= dyUdy τν / )より

( )∫+

++++

⋅−⋅=δ

σσδδ

θ0

11

dyuu (12)

と変換できる．同様に(3)式は

+

⋅=

δσ

δθ x

F

RC

2

1 (13)

ただし， ν/UxRx = ：平板長さ xに対するレイノルズ数

となる．よって(12)，(13)式より

( )∫+

=⋅− +++δσ

0 2

11 xFRCdyuu (14)

の関係が得られる．左辺の積分を計算することで，(14)式は

( ) ( ) xFRCFF2

121 =⋅− ++ δσδ (15)

ただし，

( ) ( )( )++ Π+= δκ

δ 11

1F ， ( ) ( )

+Π+Π

+=+

ππ

κδ

SiF 12

2

32

1 22

22

( ) ∫=π

θθθ

π0

sindSi ：積分正弦関数

と表される．

ここで，無次元摩擦速度σ には，局所摩擦抵抗係数 fc との間に

f

w cUU

U

2

12

==≡ρτ

σ τ (16)

という関係がある．また，局所摩擦抵抗係数 fc と平板摩擦抵抗係数 FC には，(3)式の微分と(1)

式から

fF

x

FF

F cCxdR

dCUCx

dx

dC

dx

d

2

1

2

1

2

1

2

1

2

1=+=+=

νθ

となり、

49


x

FxFfdR

dCRCc ⋅+= (17)

という関係が得られる．よって無次元摩擦速度σ は

2

x

F

xFdR

dCRC ⋅+

=σ (18)

と表される．(15)，(18)式より，

( ) ( ) xFx

FxF

RCFdR

dCRC

F2

1

221 =⋅

⋅+

− ++ δδ (19)

が成り立つ．ここで， ( )xnL RR ln= という変数変換を行うと，

nL

F

xx

F

dR

dC

RdR

dC 1=

(20)

となることから，

nL

F

dR

dCX = (21)

とおけば，(19)式から

( ) ( ) ( ) ( ) 0exp2

1

2, 21 =⋅−⋅

+−= +++

nLFF RCF

XCFXf δδδ (22)

のように砂粗面での平板摩擦抵抗係数 FC を算定する微分方程式が得られる．

しかしながら，この式は nLF dRdCX /= と+δ の２つの未知数を持つ方程式であるから，これだけで

は，粗面での平板摩擦抵抗係数 FC を算定することができない．そこで，平板乱流境界層外端で，流

速が一様流速となることを考慮すれば，(7)式より，無次元摩擦速度σ を用いて，(23)式が成り立つ必

要がある．

( ) ( ) ( )++

+ ⋅+−Π

++= kC 3.01ln12

ln11

κκδ

δκσ

(23)

また，式中，粗度レイノルズ数+k は，定義式から無次元摩擦速度σ を用いて

L

kR

L

k

R

RR

L

k

x

LR

U

U

x

kUx

U

UkUk n

x

nxx ⋅⋅=⋅⋅⋅=⋅⋅⋅===+ σσ

νντττ (24)

ただし，

=νUL

Rn ：平板長さに対するレイノルズ数

となることから，(23)式は

( ) ( )

⋅⋅⋅+−Π

++=+

+

L

kRC nσ

κκδ

δκσ

3.01ln12

ln11

(25)

となる．この式に(18)を代入し，先ほど用いた変数変換を行うことで，

( )

( ) ( )0

23.01ln

12ln

12

,

=

⋅⋅

+⋅++

Π−−−

+

=+

+

+

L

kR

XCC

XC

Xg

nF

F κκδ

δκ

δ

(26)

を得る．(26)式も(22)式同様 nLF dRdCX /= と+δ の２つの未知数を持つ方程式であり， Lk / を与え

れば，(26)式と(22)式を連立させて解くことで，各レイノルズ数に対して nLF dRdC / と+δ が得られ

るから順次 nLF dRdC / を積分すれば平板摩擦抵抗係数が得られる．

50


2. 平板摩擦抵抗係数に与える粗度影響の計算例 (1) 計算条件

平板長さ：L=300 [m]

粗度高さ：k=0, 0.03, 0.3, 3, 30, 150 [µm]

計算レイノルズ数：Rn=1.0*105 ~ 1.0*10

9

(2) 計算結果

Fig. 2 Frictional resistance coefficient of flat plate with sand roughness

Fig.3 Frictional resistance coefficient of flat plate with sand roughness in high Reynolds number.

105 106 107 108 1090

0.2

0.4

0.6

0.8

1

1.2

1.4

Rn

CF*10

2

k=0 (smooth)

k=0.03[µm]

k=0.3 [µm]

k=3 [µm]

k=30 [µm]

k=150 [µm]

107 108 1090

0.1

0.2

0.3

0.4

0.5

Rn

CF*10

2

k=0 (smooth)

k=0.03[µm]

k=0.3 [µm]

k=3 [µm]

k=30 [µm]

k=150 [µm]

51

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53

摩擦抵抗低減ストラテジ研究委員会資料

平成 22年 10月 8日

後流関数を考慮した平板摩擦の粗度影響について

- 阪大の方法との比較 -

神戸大学大学院海事科学研究科

勝井辰博

1. 速度一定の場合 (実線：神戸大学、破線：大阪大学)

計算条件

速度：U=8.0,12.0,16.0,20.0,24.0 [knot]

粗度高さ：k=0.0,100.0,160.0,240.0,320.0,400.0 [µm]

計算レイノルズ数：Rn=1.0*106 ~ 1.0*1010

　k=400.0μm　k=320.0μm　k=240.0.μm　k=160.0μm　k=100.0μm　k=0.0μm

U=8.0(knot)

106

107

108

109

1010

0.002

0.004

0.006

0.008

0.01

0.012

U=8.0(knot)

k=400.0μmk=320.0μmk=240.0μmk=160.0μmk=100.0μmk=0.0μm

Rn

CF

　k=400.0μm　k=320.0μm　k=240.0μm　k=160.0μm　k=100.0μm　k=0.0μm

U=12.0(knot)

106

107

108

109

1010

0.002

0.004

0.006

0.008

0.01

0.012

U=12.0(knot)


Rn

CF

54


平成 22年 10月 8日


U=16.0(knot)

106

107

108

109

1010

0.002

0.004

0.006

0.008

0.01

0.012

U=16.0(knot)


Rn

CF


U=20.0(knot)

Rn

CF

106

107

108

109

1010

0.002

0.004

0.006

0.008

0.01

0.012


U=20.0(knot)

55


平成 22年 10月 8日

2. 平板長さ一定の場合(実線：神戸大学、破線：大阪大学)

計算条件

平板長さ：3.0[m]

速度：U=1.0~10.0 [knot]

粗度高さ：k=0.0,100.0,160.0 [µm]

計算レイノルズ数：Rn=1.0*106 ~ 2.0*107


U=24.0(knot)

106

107

108

109

1010

0.002

0.004

0.006

0.008

0.01

0.012


U=24.0(knot)

Rn

CF

106

107

0.002

0.003

0.004

0.005

0.006

Rn

CF

k=0.0μm(OSAKA)k=100.0μm(OSAKA)k=160.0μm(OSAKA)k=0.0μm(KOBE)k=100.0μm(KOBE)k=160.0μm(KOBE)

56

日夏、川島委員の発表資料

NMRI 流体設計系「平行平板曳航法による平板の摩擦抵抗評価」では、様々な水槽試験で

の影響を除去して高精度に平板摩擦抵抗を計測する方法について示され、適用例が示され

た。

日夏、川島「摩擦応力計測法について」では摩擦応力の計測法について広範囲にレビュー

した結果を紹介した。

57

1

平行平板曳航法による平板の摩擦抵抗評価

海上技術安全研究所流体設計系

研究の背景と目的

・塗料の種類による摩擦抵抗の差を精密に評価したい

・1%程度の摩擦抵抗の差を正確に評価することが目標

船舶の全抵抗の内、摩擦抵抗成分が50%～80%を占めるため、摩擦抵抗の低減が可能であれば、船舶の省エネ化に有効

NEDOプロジェクト海水摩擦抵抗を低減する船舶用塗料の基礎技術の研究開発

58

2

開発目標

●塗料の種類による摩擦抵抗の差を精密に評価する。●外部流れでの摩擦抵抗を評価する。●発達した乱流境界層での摩擦抵抗を評価する。●なるべく実船に近いレイノルズ数で摩擦抵抗を評価する。●実船と同程度の局所摩擦応力（剪断応力）の条件で摩擦抵抗を評価する。●１％程度の摩擦抵抗の差を評価可能とする。

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

L (m)

τw

実船14kt

平板4m/s

平板4.5m/s

L

V

µVLRe

×=

µ

：代表長さ

：速度

：動粘性係数

長水槽での摩擦抵抗評価における誤差要因

長水槽における曳航試験で摩擦抵抗を評価する場合の誤差要因

●計測系起因の誤差・検力計の精度・計測装置の可動部、摺動部の摩擦、変形部のバネ定数等の誤差・計測値の振動と平均値の求め方●水槽試験起因の誤差

・静振、残留、水温の不均一と変化、レール高さ、速度制御●抵抗成分の影響・造波抵抗成分、形状抵抗成分、浸水表面積に占める被検部面積の割合、造波による浸水表面積の変化●被試験体の影響・模型の製作精度、模型の設置状態・乱流遷移の安定性

59

3

平行平板曳航法の精度向上のための工夫

●２枚の試験用平板を同時に曳航・計測することで、水槽内の残流、静振、温度勾配、レール高さの変動、曳航台車の速度変動、計測区間の設定などの誤差要因が、両平板におなじように影響を与えるようにして、緩和させた。●試験用平板は前後の板バネを介してブランコ式にぶら下げることで、摩擦・摺動抵抗の影響を無くし、装置起因のヒステリシスが小さくなるようにした。●試験用平板は、高精度圧延アルミニウム板に、精密に機械加工した整流部を取り付ける構造として、個体差により生じる誤差を小さくした。●長さ2.25m厚さ10mmのごく薄い平板模型を用いることで、造波抵抗成分、形状抵抗成分が極力小さくなるようにした。●流体力学的な干渉の影響が無視できる距離をCFDにより計算して平板の間隔を2.0mとした。●後部整流覆いに設置した高精度水温計で水温を常時モニタ。

平行平板曳航法による摩擦抵抗計測装置

2250(mm)

平板間距離2000(mm)

喫水線

760(mm)

側面図正面図

2250(mm)

平板間距離2000(mm)

喫水線

760(mm)

側面図正面図

試験用平板全長 2250mm(内前後250mmは、円弧翼型フェアリング)全高 1160mm（喫水760mm）厚さ 10mm

平板の間隔 2000mm検力計抵抗計測用１分力計２台（定格200N、誤差0.02%）平板の固定方法平板の進行方向の軸のみ自由、他は拘束吊り下げ方式板バネ方式乱流促進スタッド方式（2mm角、高さ2mm、間隔10mm、1条）試験平板の取付調整レーザーシート光を基準面とする

60

4

計測方法模式図（抵抗計測時）

板バネ

検力計

進行方向

試験用平板

曳航ロッド

側面図

摩擦抵抗計測方法模式図

検力計

曳航ロッド

検力計と曳航ロッドの取り付け状態

61

5

前部整流覆いと乱流促進装置平板をつり下げる板バネ

乱流促進装置とブランコの板バネ

板バネ

乱流促進装置（2mm角立方体を

10mm間隔で配置）

試験用平板取り付け調整方法

計測レールの駒を基準にレーザーシート光で基準面をつくる

平板とレーザーシート光の距離を計測する

レーザーシート光を基準面にして試験用平板を取り付け・調整する。

62

6

計測装置水槽設置状態

乱流状態の確認

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0.005

0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07

Re

CT, CF

CT (FAPB)CT (FBPA)CF (Shoenherr)CF*1.03

Shoenherrの式で求められる摩擦抵抗係数との比較

全抵抗係数、摩擦抵抗係数

63

7

抵抗成分の分離

endbottomedgetrailingsurfacetestedgeleading RFRFRFRFRRRT −−−− ++++=

RT ：全抵抗 RR：剰余抵抗（造波抵抗及び形状抵抗）

edgeleadingRF −：前部整流覆の摩擦抵抗 surfacetestRF −

：検査面の摩擦抵抗

edgetrailingRF − ：後部整流覆の摩擦抵抗 endbottomRF − ：下部整流覆の摩擦抵抗

前部整流覆

乱流促進

喫水線

検査面 11

50m

m

75

0m

m

125mm 125mm

2000mm

後部整流覆

10mm

下部整流覆い

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.5 1 1.5 2 2.5 3 3.5 4 4.5

試験速度(m/s)

剰余抵抗

整流覆摩擦抵抗部分

試験部摩擦抵抗成分

抵抗成分の割合

64

8

検力計を装置に取り付けた状態での精度を以下に示す。精度の確認は平板を取り付けた状態で、校正用プーリーを用いて定格容量の490Nまで実施。

490N

490N

定格

0.06

0.04

0.06-0.06左検力計

0.07-0.03右検力計

ヒステリシス

(%)直線性

(%)

計測装置の精度①

計測装置の精度②（精度確認試験）

・試験対象同一寸法、同一形状の無塗装アルマイト地肌の基準板

・抵抗試験速度範囲

0.5m/s～4.5m/sRe数：1×106～1×107

・繰り返し試験速度：4.0m/s試験回数：10回

65

9

整流部、板の交換による整流部固有抵抗差の確認FA：フェアリングA、FB：フェアリングB、PA：平板A、PB：平板B

左右の前部フェアリングの固有抵抗の差が0.3%程度あることが判った。

計測装置の精度③整流部の固有抵抗

-1.50%

-1.00%

-0.50%

0.00%

0.50%

1.00%

1.50%

2.00%

0 1 2 3 4 5

Vm[m/s]

全抵抗の差[%]

FBPA-FAPBFAPA-FBPB（フェアリング交換）FBPA-FAPB（フェアリング戻し）FAPB-FBPA（平板左右交換）

-1.00%

-0.80%

-0.60%

-0.40%

-0.20%

0.00%

0.20%

0.40%

0.60%

0.80%

1.00%

0 1 2 3 4 5 6 7 8 9 10 11

Test Number

dR/R[%(15℃)]

FAPB-FBPA（4m/s）

左右平板の抵抗差（％）

計測装置の精度②繰り返し試験結果①

同一形状・材質の試験用平板２枚の繰り返し試験結果（4m/s）計測された全抵抗値の差は0.18％の範囲に分布

0.18%

66

10

計測装置の精度③繰り返し試験結果②

全抵抗値の分布の範囲は、左側平板で0.46%、右側平板で0.45%左右の平板を同時に計測することにより、試験状態の相違が緩和されていることが判る

-1.0%

-0.8%

-0.6%

-0.4%

-0.2%

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

0 1 2 3 4 5 6 7 8 9 10 11

Test Number

平板抵抗値の平均値との差（％）

Right plate（4m/s）Left plate(4m/s)

0.45%

0.46%

同一形状・材質の試験用平板の検査面を左右取り替えて計測平板の脱着による差は最大で0.1%程度

計測装置の精度④平板の脱着

0.00%

0.05%

0.10%

0.15%

0.20%

0.25%

0.30%

0.35%

0.40%

0.45%

0.50%

5.0E+06 6.0E+06 7.0E+06 8.0E+06 9.0E+06 1.0E+07

Re

dR/R[%]

FAPA-FBPB

FAPB-FBPA

左右平板の抵抗差（％）

0.1%程度

67

11

舶用塗料の評価①（試験条件）

・試験対象無塗装アルマイト地肌の基準板加水分解型塗料A塗装板シリコン系塗料B塗装板サンドブラスト加工粗度板

・速度範囲0.5m/s～4.5m/sRe数：1×106～1×107

加水分解塗料A シリコン系塗料B

舶用塗料の評価②（塗膜の厚みの影響の補正）0 0.1 0.2 0.3 0.4 0.5 0.6 0.75 average

Bare plate 10.00 10.00 9.99 10.00 10.00 10.00 10.00 10.00 10.00Paint A 10.56 10.50 10.54 10.48 10.49 10.47 10.47 10.49 10.50Paint B 10.97 10.98 10.93 10.94 10.92 10.92 10.94 10.98 10.95

depth (m)

thickness(mm)

0CRCRDCR sheets −=

sheetsCR ：厚みが付加された状態での剰余抵抗係数

0CR：厚みが付加されていない状態での剰余抵抗係数

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 0.2 0.4 0.6 0.8 1

DCR/CR

Additional thickness of the plates (mm)

With 6 sheets

With 12 sheets

68

12

舶用塗料の評価③（摩擦抵抗計測結果）

0.0027

0.0029

0.0031

0.0033

0.0035

0.0037

0.0039

0.0041

0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07

Re

CF

Bare plate 1 （vs Roughness）

Bare plate 2 (vs Paint A)

Bare plate 3（vs Paint B）

Paint A (vs Bare plate）

Paint A (vs Paint B）

Paint B (vs Bare plate)

Paint B （vs Paint A）

Roughness (vs Bare plate)

舶用塗料の評価④（同時計測の摩擦抵抗の評価）

0.99

0.995

1

1.005

1.01

1.015

1.02

1.025

1.03

1.035

0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07Re

CF/CF

Roughness／Bare plate

Paint A／Bare plate

Paint B／Bare plate

Paint B／Paint A

69

13

舶用塗料の評価④（試験平板の表面粗度）

非接触レーザー変位計30mm×30mm

2Ra Rzjis Rz RzPaint A 3.22 6.48 10.48 100Paint B 0.74 1.64 2.62 106Roughness plate 15.04 33.86 48.59 61

2.5mm×1.9mm走査型共焦点レーザー顕微鏡

粗度(μm)

測定範囲粗度定義

粗度と摩擦抵抗の関係（Schlichtingの図表から）非接触レーザー変位計

30mm×30mm2Ra Rzjis Rz Rz

Paint A 6.99E+05 3.47E+05 2.15E+05 2.25E+04Paint B 3.04E+06 1.37E+06 8.59E+05 2.12E+04Roughness plate 1.50E+05 6.65E+04 4.63E+04 3.69E+04

粗度定義

粗度（k/L)

走査型共焦点レーザー顕微鏡測定範囲 2.5mm×1.9mm

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

0.E+00 5.E+04 1.E+05 2.E+05 2.E+05 3.E+05

L/k

CF(rough)/CF(smooth)

70

14

まとめ

・左右の平板を同時に計測することにより、水槽試験につきものの計測毎の条件の相違が緩和され、抵抗の差がより精度良く評価できる。

・繰り返し試験の結果、左右平板の抵抗差の再現性は非常に高い。

・摩擦抵抗の差1%以下の２種類の船舶用塗料の摩擦抵抗を評価できた。

・塗膜の表面粗度は、波長の大きいうねり成分ではなく、波長の短い粗度で評価する必要がある。

謝辞

本研究は (独)新エネルギー・産業技術総合開発機構による「海水摩擦抵抗を低減する船舶用塗料の基礎技術の研究開発」の一部として実施しました。ここに謝意を表します。

71

摩擦応力計測法について

摩擦抵抗低減ストラテジー委員会

平成23年1月21日海技研日夏宗彦、川島英幹

摩擦応力計測法(チャンネル流）についてのレビュー

摩擦応力計測法について、1950年代から70年代にかけて活発に行われた。

今回の紹介ではチャンネル流にとらわれず、摩擦応力計測法に関する過去の文献から、以下の４件を取り上げて、紹介することとする。これらの論文では、摩擦応力計測法に関するレビューや考察が詳細に記述されており、一読しておく価値のある文献と思われる。

1)Direct Measurements of Skin Friction, b y S.Dhawan, NACA Report 1121 (1953)

2）Skin-Friction Measurements in Incompressible Flow, by D.W.Smith & J.H.WalkerNACA-TN-4231, (1958)

3) Calibration of the Preston tube and limitations on its use in pressure gradients, by V.C.Patel, JFM vol23, part 1, 185-208 (1965)

4) The Measurement of Skin Friction in Turbulent Boundary Layers with Adverse Pressure Gradients, by K.C.Brown, P.N.Joubert, JFM Vol.35 part 4, 737-757 (1969)

72

摩擦応力計測法(チャンネル流）についてのレビュー

我が国(船舶系）においても下記のような摩擦応力計測に関する研究が行われている。

（今回は紹介を割愛した）

1)A New Skin Friction Meter of Floating-Element Type and the Measurements of Local Shear Stress by T.Hotta, JSNAJ Vol. 138, (1976)

2）表面粗度による抵抗増加に関する研究（第１，2報）､山崎､小野木他、造論153号(1983)、155号(1984)

3)油膜を用いた限界流線と壁面摩擦応力の計測、奥野他、造論176号、(1994)

4)船体表面の摩擦応力分布および境界層内の2次流れに関する研究、奥野、造論139号、(1976)

なお、今回のレビューの最後に光学的手法による最近の論文を簡単に紹介した。先の英文４件とは異なる手法であるため、新しい動向の自答という位置づけで取り上げた。

また、ここで紹介する４件の英文論文や上記の論文は著名なものばかりなので、既に読まれた方がほとんどと思われるが、復習の意味も込めてご容赦願いたい。

Dhawan の論文

概要：超音速域での摩擦抵抗式を求める。従来の計測法についてのレビューをした結果、直接法を採用した。本論ではレビュー内容が詳細に述べられている。

直接法に対しても、圧縮性流体を視野に入れているので、温度計測による方法もレビューしている。最終的には直接摩擦応力を計測する方法を採用。

Floatingタイプの方法を採用。・floatingタイプの場合、センサー板と支持部のgap影響は？ Gap前後の境界層速度分布を計測。

影響なしと判断。

73

Dhawan の論文

微小力の計測方法：いくつかの方法があり、それぞれについてレビューの後、reactanceタイプを採用。外部の振動影響を除去、温度変化(±20度）による出力変化がないことを確認。

計測部のピックアップ部

風胴に取り付けられた摩擦応力計測装置の詳細(図では0.2cmx2cmの受感板だが、これは音速用）(非圧縮、低音速の場合は、1.15cmx6.3cmとした）

校正では、直線性、繰り返し荷重による再現性等も確認した。

Dhawan の論文

実験時のセットアップ：受感板が長方形のため、tilt影響による

誤差修正も考慮。

境界層速度分布計測例層流境界層の判定として、熱線データからTS波が検出されるか否かでも判断

74

Dhawan の論文(圧縮性の部分は省略）

摩擦応力係数の結果非圧縮の場合）

層流の場合、計測した速度分布と右図に示す圧力勾配データからzero圧力勾配下のデータに修正。乱流の場合、1/7乗則で速度分布を近似

Smith & Walkerの論文

概要：Zero圧力勾配下での摩擦応力計測について詳述。3つの方法で計測。・境界層速度分布計測から境界層パラメータを求め運動量積分式からcfを計算。・直接法：floatingタイプ・Preston管

試験のセットアップ（単位はインチ）

前縁の小孔から空気を吹き出して、遷移させている

75


境界層速度分布計測用の平型Pitot管摩擦応力計測装置


Preston管ゼロ圧力勾配の確認

乱流境界層の見かけの始点は、d(log 2θ)/dxで決定

76


境界層速度分布計測例

乱流境界層の見かけの始点は、d(log 2θ)/dxで決定

形状係数Hとレイノルズ数の関係


77


境界層速度分布結果から運動量厚さ経由でCFを推定した値と、Ｃｆ計測結果を積分し

た結果の比較


今回の結果(tableIV)と従来の試験結果の比較

78


今回の結果(tableIV)と従来の試験結果の比較


直接摩擦応力計測法とPreston管で得た結果の比較。Preston管の方が小さいが、Prestonの校正曲線が正しくないことが原因と考えられる。(Patelらの指摘に通じる）

79

V.C.Patelの論文

概要：Preston管による摩擦抵抗計測法を考案したPrestonが提案した式は誤差が大きい。正し

い、校正式を提案する。さらに圧力勾配下で、この式がどの程度正しいか見極める。

試験方法：パイプ流れを用いる。真とする摩擦抵抗の値は圧力降下で求める。14種類のPreston管で試験。(圧力勾配の影響小のとき）

V.C.Patelの論文

境界層を下記3つの領域に分ける。て、それぞれについて定式化

それぞれについて下記のように定式化

80

V.C.Patelの論文

圧力勾配があるとき

右図のような実験装置で実験

Ｐｒｓｔｏｎ管には新たにフェンスが設けられている。

フェンス前後の圧力差を計測

前述の校正曲線が圧力勾配下でどの程度使えるのか調べルことを目的としたが、難しいことがわかった。

圧力勾配下での速度分布の考察を行う。

V.C.Patelの論文

Preston管の読みとフェンス前後の圧力差の読みが圧力勾配の影響を受けないとすると、これらの関係は一つの線に乗る。しかし、実際はPreston管の読みとフェンス前後の圧力差の関係が一つの曲線に乗らない。Preston管は圧力勾配下では摩擦力を過大評価している傾向にあるように見える。順圧力勾配下では、Preston管径

が小さくなるほど、誤差は増加。当初の予期とは異なる。速度分布の変化にテーマを変えた。

81

V.C.Patelの論文

Δ=

著者が導いたPreston管の使用限界

速度は0.054インチ径のピトー管で計測摩擦応力はフェンス前後の圧力差で決める。(別途校正）

Brown & Joubertの論文

概要：逆圧力勾配下での摩擦抵抗計測を行う。種々の方法をレビューし、その結果直接計測法を採用。

著者らの摩擦応力計測法の分類

論文では上記手法について興味深いレビューがされている。

82


直接計測法の模式図。ギャップによる影響について考察されている。

右図は著者らの摩擦応力計測装置

Aの計測部の直径は3/4インチギャップは.003インチ、Cの青銅板バネで支持、Dはダンパーで風洞の振動影響を除

去


キャリブレーションの方法(2種類でチェック） (b)では糸の角度が必要、写真で読み取る。

試験風洞

総圧管の径：0.04インチPreston管の径:0.0362、0.029、0.02インチPreston管の校正係数はPatelの結果を使用

83


結果

Clauserの方法は、次ページに示すClauserのチャートに境界層速度分布をプロットし、Cfを補間して決定直接法とPreston管の違いは、圧力勾配によるslight secondary force、アラインメントの誤差等の影響と考えられ

る。


84


圧力勾配下での結果Preston管と速度分布から摩擦応力を決める。圧力勾配下でのPreston管の精度限界マップ

Patelの6%リミットは楽観的


直接法における圧力勾配によるsecondary forceの影響マップ摩擦応力はPreston管の読みを用いた。

1.0のときsecondary forceの影響なし

85

最近の論文より

COHERENT STRUCTURES AND THEIR CONTRIBUTION TO TURBULENTINTENSITY IN TURBULENT CHANNEL FLOW

S. Imayama、Y.Yamamoto、YTsuji（名大辻先生より原稿入手）

最近の論文より

uk:フリンジ速度, n:屈折率、Δh：両隣のフリンジ高さの差 h0：オイルフィ

ルム端の最初のフリンジ高さ

86

戸田委員による報告の概要

１．資料１の論文と発表資料により、空気潤滑法であるがこの結果により摩擦抵抗低減が

あるとプロペラ面流速（1-w）に変化があり、この場合は同じ回転数、同じ CPP 翼角

で摩擦抵抗が減ると、船速はほとんど増加せず、馬力が下がる。これを推力、トルク

計測を行なっていたため抵抗が小さくなり、1-w が大きくなっていることがわかったこ

とを説明し、抵抗が下がっても単純に速度が上がる場合ばかりではないことを説明し

た。これにより摩擦抵抗が変わると当然 1-w の推定もやり直す必要があること、推力

を実船で計測が可能であれば直接船体抵抗に関連するものが取られるということを説

明し、燃料消費や馬力での検討より少し細かい内容が分かることを説明した。

２．資料２の論文と発表資料（報告書では省略)により、塗膜の種類によっては同じような

幾何学敵粗度であっても、抵抗が異なる場合があること、かなり平滑面に近づくよう

な場合もあることが紹介された。回転円筒装置と 3m の模型船を使った検討で、ある種

の親水性塗料では浸漬後計測すると等価砂粗度がかなり小さくなり、この等価なもの

を用いて実船を推定した結果なども示された。またこの推定により同じ等価砂粗度高

さで長さを変化した時の変化を ITTC の手法と比較して説明した。現在の ITTC の相関

に関するものと粗度に関するものの粗度の部分とは少し異なる傾向があることを示し

た。

３．資料３のパワーポイントにより、粗度の影響を考慮した境界層計算を行い、等価砂粗

度が変わる塗膜を半分塗る場合、前半でも後半でも同じことを示した。これは境界層

厚さの発達が異なるためで、資料４の空気潤滑でも同じことが得られることやこれは

青雲丸の実験でも見られたことなどが紹介された。

４．資料４により大学のような専門家がいないところでは浮かす単純船型模型による実験

が今までの経験上再現性が高く、その方法を様々な塗膜に行い、データベースにより

さまざまな塗膜にたいする実船推定法の考察を示した。

５．深江丸のドック前後の推力、トルク計測結果を示し、推力トルク計測を行うことで汚

損の船体への影響とプロペラへの影響が分離可能ではないかという報告がなされた。

資料５

６．ITTC の表面処理委員会のレポート（資料６）と、グループディスカッションでの関連

講演の資料（資料７）が示され概略が説明され、粗度計測装置について概略が示され

た。これは資料４に示した。

７．なお山盛オブザーバによる解説も戸田委員よりお願いしたのでここに資料 8 として入

れる

87

Full scale experiment for frictional resistance reduction using air lubrication method

C.L. Hoang, Y. Toda, Y. Sanada Department of Naval Architecture and Ocean Engineering, Graduate school of Engineering, Osaka University

Suita, Osaka, Japan

ABSTRACT This paper describes the full scale experiment using air lubrication method to reduce the frictional resistance. The full scale experiment with the cement carrier Pacific Seagull was conducted from January to March, 2008. Torque and thrust are decreased due to the effect of bubbles. If we assume the value of thrust deduction is constant with and without bubbles, the effect of bubbles in reducing frictional resistance or ship resistance is clearly proved by the experimental results. The maximum total resistance reduction in case of ballast condition and full load condition are about 11% and 6% respectively. The mean propeller inflow velocity was increased for with air lubrication from no air condition due to the viscous resistance reduction. This phenomenon was considered using very simple boundary layer method. KEY WORDS: Full scale experiment; energy saving; air lubrication; frictional resistance reduction. INTRODUCTION

Air lubrication method is a promising method to reduce frictional resistance which is nearly 70% of total resistance of low speed ship. Bubbles were injected at the fore bottom part of the ship. After injection, it is expected that bubbles will cover all the bottom part downstream and take effect on local frictional resistance reduction. In 2002, the full-scale experiment was carried out in SR 239 project for the first time using the training ship Sein-maru. The net energy saving in that experiment was 2% at air injection rate 40 m3/min. Based on this result, the effect of bubbles on frictional resistance reduction of ship was proved (Nagamatsu et al. 2003).

Three years later, in 2005, the second full-scale experiment was done using the cement carrier Pacific Seagull. This ship has a box shape hull and was equipped with blowers which could be used to supply air for bubbles. However, injected bubbles did not cover the bottom of ship sufficiently so maximum frictional resistance reduction was only 1% at air injection of 50 m3/min (Kodama et al. 2007).

Based on the results and accumulation of experience obtained from

the previous two experiments, the full-scale experiment using the same ship, Pacific Seagull, was carried out in 2008.

This full-scale experiment was conducted by the cooperative

research project with National Maritime Research Institute Japan (NMRI), Hokkaido university, Osaka university and Azuma shipping company. New Energy and Industrial Technology Development Organization (NEDO) sponsored for this project. Kodama (2008) showed a brief summary of this full-scale experiment with about 4% net fuel consumption reduction in case of full load condition and 7% in case of ballast condition. In this paper, the results from shear stress, thrust and torque measurement done by the authors are presented and considered using simple momentum integral equation of the boundary layer. The data was taken from January 6th to 11th, 2008.

EXPERIMENTAL EQUIPMENTS General Arrangement of Experimental Equipments

The principal dimensions of Pacific Seagull ship are shown in table 1. In order to conduct the full scale experiment, the ship was equipped with experimental equipments such as blowers, cameras, ultrasonic velocity profiler (UVP), thrust and torque gauge on the propeller shaft, shear stress sensor on the hull surface and etc.

There are 5 sets of blowers, 3 on starboard and 2 on the port side.

The pressure is 100 kPa. The ability of air supply of one blower is about 22 m3/min, so maximum bubble generation is 110 m3/min. Air was fed from blowers to bubble generation device using the related piping system which was installed from the main deck to the bottom of ship. Three cameras were installed at propeller plane, bubble injector position and near shear stress sensors position. The main purpose of these cameras is to capture the images of bubble when blowers were active.

In order to keep bubble more efficiently inside the bottom area of

ship, end plates were welded along the side end under the bottom of ship. These end plates have the same height of 0.15 m and the total length of end plates is 47.2 m. Figure 1 shows the general arrangement of equipments in full scale experiment. Overall brief description of experiments was shown in Kodama(2008).

88

Table 1. Principal dimensions of Pacific seagull

Length over all 126.6 m Length between perpendiculars 120.0 m Breadth 21.4 m Depth 9.9 m Draft (designed full) 7.1m Draft (Full experiment) 7.0 m even Draft (ballast) in experiment 4.0 m (trim by stern 1.5 m) Speed (service) 12.4 kt Main engine 3883 kW x1 Propeller 4 blades CPP Diameter of propeller 3.6 m

Strain Gauge and Shear Stress Sensor

To measure the thrust and torque, the strain gauges were attached on the shaft directly and to minimize the temperature effect, Hylarides method (Hylarides, 1974) with dummy plate and temperature insulation using two direction strain gauges were employed to measure thrust and torque. In figure 2, two pictures on top were focused on the images of torque gauge and thrust gauge. To minimize the misalignment, the 10mm gauge length was used for measurement as shown in Fig. 2. Here, torque gauge is the strain gauge on the left and thrust gauge is the strain gauge on the right. The remain two pictures of Fig. 2 show the installation work from the beginning when the first strain gauges were glued on propeller shaft to until the entire job have been done. Preamplifier with transmitters and batteries were tied with belts around the shaft. After finished the installation, propeller shaft was covered with thermal insulation material. The system which was constituted from these strain gauges will detect thrust, torque and temperature and transmit the measuring data as radio signals to the data acquisition system via telemeter.

Figure 3 shows the images of shear stress sensor before and after it

was installed under the bottom of the ship in the dockyard. As shown in the left figure, the sensing plate was held with three blade springs and frictional stress was detected by load cell. The sensing plate was made of acrylic resin and in a square shape with dimensions of 200 mm x 200 mm, 5 mm in thickness and 238 g in weight. The height of sensor was quite thin and 27 mm. The right figure shows the installation by stud bolts. After this installation, the fairing plate was installed as shown in the bottom figure. It was suitable for mounting sensor to the ship surface smoothly with fairing. Fairing plates were installed to the sensor to reduce the height difference between the sensor plate and the surrounding surface. Detailed information and structure of this sensor

are shown in Toda et al.(2005) and the size of the fairing plate was changed to 1174x1174 mm to reduce the effect of the mound. The flat part is 400x400 mm, so the 27 mm height is reduced using 387 mm slope (less than 1/14). In this experiment, 3 sensors were installed under the bottom of the ship. 2 sensors were on the starboard and the other one was on the port side. The position of these sensors was 50 m toward the stern direction from the bubble injection position.

Air pipeBubble generator Thrust and torque gauge

Blower

End plate

Shear stress sensor UVP transducers

Camera

Fig. 2 Thrust gauge and torque gauge

Fig. 1 General arrangement of equipment

Fig. 3 Shear stress sensor EXPERIMENTAL RESULTS

During the operation of ship, the large difference in ship speed between with and without bubble injection was not observed. The measurements were carried out for full load and ballast conditions and the blade pitch angle of controllable pitch propeller was changed to change the average speed.

Figure 4 shows the example of shear stress measurement results for

sensor No. 1 (near the bilge keel on starboard side) and sensor No. 2 (near the centre plane). From the figure, the clear reduction of local skin friction for both sensors can be seen at 50 m downstream from the injection point and the time lag from the start time of blower operation due to the distance from the injection point. It shows that the effect of bubbles remains whole bottom area and the larger reduction seems to be obtained in the upstream region. This result can be referred to the result obtained from the 50 m model experiment in NMRI (Kodama et

89

al. 2007). From the figure, the amount of reduction depends on the location and the reduction rate is larger near the centre plane. About 40% reduction was observed for sensor No. 2.

Figs. 5~6 show two examples of thrust and torque measurement in two cases: ballast condition and full load condition. As shown in these figures, torque and thrust are decreased due to the effect of bubble and similar time delay can be observed due to the distance between the injection point and the propeller. The value of thrust deduction can be assumed constant with and without bubble, because the main cause of thrust deduction is the upstream pressure drop by producing the thrust. So, in this case the total resistance seems to be reduced about 10% in Fig. 5 and about 5% in Fig. 6. The total resistance reduction of the ship is about 11% and 6% in case of ballast condition and full load condition, respectively.

In experiment, number of revolution was fixed, so the torque

reduction means the power reduction. It means that the fuel consumption should be reduced by this reduction.

0 500 10000

1

2

3

4[×105]

Without bubble and with bubble by 2 blowers (No.3,4)Propeller pitch 16.2degree, ship speed 13.1kt and 12.9kt

Blower Off Blower On

Thrust (N)~ 5%reduction

Torque(N.m) ~ 5%reductiont(s)

Shearing Force (N) Shearing Force (N)

∼20% reduction ∼40% reduction

Sensor No.1 Sensor No.2

t(s) t(s)

From the thrust identity analysis using measured thrust and the propeller open characteristics measured in NMRI, the effective mean velocity at propeller plane is estimated. Figure 7 shows the ratio of resistance and effective wake fraction between with and without bubble. As showed in this figure, with the appearance of bubble, ratio of resistance decreased opposite with the increasing tendency of ratio of effective wake fraction. It means the mean flow in the propeller plane increases due to the skin friction reduction.

Total resistance consists of 30% wave making resistance and 70% viscous resistance based on full scale prediction from model experiment. The ship which was used in full-scale experiment has large bottom area and this area is nearly 50％ of wetted surface area in ballast condition. The effect of bubble was only observed at the bottom of ship. It means that 11% total resistance reduction obtained in experiment is the reduction in viscous resistance of bottom part. From the above analysis, if we consider only bottom area of ship, the viscous resistance reduction of covered area by bubbles will be 35%. From Fig. 7, if resistance is reduced 11%, nearly 12% of increase of 1-w is observed. The ratio of resistance and 1-w is shown for one condition in table 2.

Propeller pitch 16 degree, ship speed 13.1 and 13.2kt

Number of blower

0.50.60.70.80.9

11.11.2

0 1 2 3 4 5 6

R/R0 (1-w)/(1-w)0R

/R0,

(1-w

)/(1-

w) 0

Fig. 4 Example of raw time history of the local shear force (acting on the sensing plate) when five blowers were active

Fig. 7 Analyzed ratio of R and 1-w between with and without bubble for ballast condition, pitch angle 16.9 degree

Fig. 6 Example of raw time history of thrust and torque without bubble and with bubble by 2 blowers in full load condition

Fig. 5 Example of raw time history of thrust and torque without bubble and with bubble by 5 blowers in ballast condition

90

Table 2. Values of 1-w, 1-t and total resistance rate when 5 blowers

were active and propeller pitch angle was set 16.9 degree.

Without bubble With bubble Total resistance ratio 1 0.89 Viscous resistance ratio of bottom area

1 0.65

1-w 0.573 0.638 1-t (assumed constant from model exp.)

0.81 0.81

From table 2, 1-w is increased by 0.65. The viscous wake wv is estimated from ITTC procedure (wv = w-wp = w-(t+0.04), wv: viscous wake component, wp: invisid wake component, 0.04: rudder effect). If wv for with bubble condition is estimated using wv is proportional to viscous resistance of bottom viscous resistance because the propeller plane flow almost comes from the bottom area, predicted 1-w is 0.642. This value is a little bit higher than the measured value, but the increase of mean velocity can be explained by the resistance decrease in bottom area considering that the density change and details of the flow field were ignored. CONSIDERATION USING SIMPLE INTEGRAL METHOD The simple integral method for two dimensional boundary layer is

employed to consider the phenomena obtained in the full scale experiment. For without bubble conditions, the following equation is well known as the simple method (Schlichting, 1979). We assume velocity distribution in boundary layer by using the 1/7 power law like in Eq. 1

17u y

U δ⎛ ⎞= ⎜ ⎟⎝ ⎠

(1)

And using the following local skin friction law

1 1

47 44

20.0225 2 0.02251

2

fU CUU

υ τ υτ ρδ δρ

⎛ ⎞ ⎛ ⎞= = =⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

i (2)

Where δ: boundary layer thickness, U: the uniform flow velocity

L: ship length, θ : momentum thickness y: the distance from the surface, ρ: the density τ: shear stress, Cf: local skin friction coefficient υ: kinematic viscosity

0

7172

u u dyU U

δ

θ δ⎛ ⎞= − =⎜ ⎟⎝ ⎠∫ (3)

The momentum integral equation is shown as the following.

2

ddx Uθ τ

ρ= (4)

Where x : the distance from the leading edge in flow direction So the momentum thickness will be obtained as follow

1470.0225( )

72ddx Uθ υ

θ= (5)

This is the well known relation and the non-dimensional form is as following. The over bar￣ represents the non-dimensional value.

1 114 4470.0225( ) ( )

72d a Rn

Rnd xθ θ θ

−−= = (6)

where 1470.0225( )

72ULa Rnν

= = : Reynolds number

After solving the above equation, momentum thickness will be represented as

41555( )

4x ax Rnθ

−⎛ ⎞= ⎜ ⎟⎝ ⎠

(7)

Using Eq. 2 with the value of momentum thickness received from Eq. 7, we obtain

15

415552

4fC a a Rn x−

−⎛ ⎞= ⎜ ⎟⎝ ⎠

(8)

When bubbles were injected, due to the effect of bubbles, frictional coefficient will be smaller. Assume that we can express the relation between Cf (local frictional coefficient with bubble) and Cf0 (local frictional coefficient without bubbles for same momentum thickness Reynolds number) like the equation below:

0( , )f a fUC k t void fraction distribution C θυ

⎛= ⎜⎝ ⎠

⎞⎟ (9)

In Eq. 9, ta is air layer thickness. The value of ta is expressed as follow.

( )a

aa

Qt (10) B U

=

where, Qa is injected air flow rate, BBa is the width of the injection plate. Therefore

1 14 4

012 f

d kC kaRnd xθ θ

− −= = (11)

To the point x = x0 (injected point), we obtain the momentum thickness using original Eq. 7. So, the momentum thickness at x0 is shown as follows

5 14

05( )4

40x aRn xθ

−= (12)

Momentum thickness at initial value of x = x0 must be the same in case of bubbles and without bubbles. So, we can obtain the momentum thickness for with bubble condition as follows

91

1 15 54 44 4

0 05 5( ) ( )4 4

x kaRn x kaRn x xθ θ− −

= − +

After transformation, this equation become

( )4

1 54

05( ) (1 )4

x aRn k x k xθ−⎛

= + −⎜⎝ ⎠

⎞⎟ (13)

From Eq. 13 the value of local frictional coefficient will be obtained as follow:

( )15

14

14

052 (14fC akRn aRn k x k x

−

− −⎛ ⎞= +⎜ ⎟

⎝ ⎠)− (14)

In case k ＝ 1/2 , Eq. 14 can be rewritten as follow:

( )15

14

14

058fC aRn aRn x x

−

− −⎛= ⎜

⎝ ⎠

⎞+ ⎟ (15)

The calculated value is decided by the value without bubbles and shown in Fig. 8. The Cf00 is the value for without bubble condition. Although we assume the constant k=0.5, the value of Cf/Cf00 is increasing towards the downstream from the injection point. This tendency is similar as the results obtained in NMRI using 50 m model with end plates (Kodama et al., 2007).

Total frictional resistance coefficient is shown as follows

12

2 0 0

1(1)1 22

L

F fRC R dx UU L

θ τ ρρ

= = = =∫ ∫L C d x (16)

Where R: total frictional resistance So, the value of frictional coefficient can be obtained by Eq. 7 and Eq. 13 for without and with bubble conditions, respectively. Fig. 9 shows the relation among the ratio of total frictional resistant

coefficient between with and without bubbles CF/CF0, injected bubble

position x0 and k. In full scale experiment, bubbles were injected at 26 m downstream from the bow. In other words, injected bubble location is about 20% from the bow when it is compared with the length of real ship. From this and the above mentioned analysis, as shown in Fig 9, in case x0 = 0.2, k = 0.5 total frictional resistant coefficient reduction between with and without bubbles is 35%. This value shows a good agreement with the aforementioned result obtained in full scale experiment. Figure 10 displays the momentum thickness for k=0.5 along with

without bubble condition at different air injection positions. The solid curve depicted the momentum thickness without bubble. At the injection points x0 = 0.2 and x0 = 0.4 momentum thickness changed to dash curve and dash dot curve, respectively. Boundary layer development will change due to the local skin friction reduction. This phenomenon could be used to explain the increasing tendency of 1-w when bubble takes effect at the bottom of ship.

x0=0.2

x0=0 x0=(0:1)

x0=1

ｋ

k= 0.5, x0= 0.2

Cf/Cf00

x

Fig. 9 CF/CF0 at different x0

k=0.5

15.Rnθ

Fig. 8 Cf/Cf00 at ｋ = 0.5, x0 = 0.2

Fig. 10 Momentum thickness at different x0

92

CONCLUSIONS The effect of bubbles in reducing frictional resistance or ship

resistance is clearly proved by full scale experiment result. The mean velocity at propeller plane is increased due to the viscous resistance reduction from the thrust measurement results. It seems the cause of the small speed gain against the large resistance reduction. The torque reduction is also observed and the required power reduction is shown. The phenomena are considered using very simple boundary layer theory. But the mechanism of frictional resistance reduction by bubbles is complicated. It is necessary to have further research to elucidate this problem. ACKNOWLEDGEMENTS This study is sponsored by NEDO and done as the cooperative

research project with NMRI, Azuma Shipping Co. Ltd., Hokkaido University and University of Tokyo. The authors appreciate of those supports. The authors would like to express the special thanks to Dr. Yoshiaki Kodama and Munehiko Hinatsu for the guidance of the project. The special thanks are extended to the crew members of Pacific Seagull.

REFERENCES Hylarides. “Thrust Measurement by Strain Gauge without the Influence

of Torque” Shipping World and Shipbuilder, Dec. 1974, pp. 1259-1260

Kodama, Y, Takahashi, T, Makino, M., Hori, T, Kawashima, H, Ueda, T, Suzuki, T, Toda, Y, Yamashita, K (2005). “microbubbles – a large scale model experiment and a new full-scale experiment” Proceedings of the 5th Osaka colloquium, pp. 62-66.

Kodama, Y, Hinatsu, M, Kawashima, H, Hori, T, Makino, M, Ohnawa, M, Takeshi, H, Sakoda, M, Kawashima, H, Maeda, M(2007). “A progress report of a research project on drag reduction by air bubbles for ships” 6th International conference on multiphase flow, ICMF 2007.

Kodama, Y et al. (2008). “A full-scale air lubrication experiment using a large cement carrier for energy saving-result and analysis”, Conference proceedings, the Japan Society of Naval Architects and Ocean Engineers, pp. 163-166 (in Japanese)

Nagamatsu, T et al (2002). “A Full-scale Experiment on Microbubbles for Skin Friction Reduction Using ”SEIUN MARU” - Part 2: The Full-scale Experiment-”, Journal of the Society of Naval Architects of Japan, No. 192.

Schlichting, H. (1979). “Boundary layer theory-seventh edition” McGraw – Hill, pp. 636-639

Toda, Y, Suzuki, T, Yuda, N, Lee, Y.S(2005). “Shear stress sensor for full-scale experiment” Proceedings of the 5th Osaka colloquium, pp. 67-75.

93

International Symposium on Marine Engineering (ISME) 2009, BEXCO, Busan, Oct. 2009

Frictional Resistance Reduction using Lower Frictional Paint

N.Yamamori 1, Y. Toda 2, Y. Yano 3 1. Nippon Paint Marine Coating Co, Ltd., 19-17 Ikedanakamachi, Neyagawa City,

Osaka572-8501, Japan, [email protected] 2. Osaka University, Department of Naval Architecture and Ocean Engineering 2-1 Yamadaoka,

Suita City, Osaka 565-0871, Japan, [email protected] 3. Kobe University, Training Ship Fukae Maru, 5-1-1 Fukaeminamimachi, Higashinadaku,

Kobe City, Hyogo 658-0022, Japan, [email protected]

Corresponding author Y. Toda

Abstract The effect of paint coating on hull surface to the ship frictional resistance is studied. The frictional resistance acting on the newly developed anti-fouling Lower Frictional paint (LFC-AF) is compared with that on the conventional Self Polishing Copolymer (SPC) through rotational cylinder tests, towing tank experiment. The viscous resistance reduction using LFC was observed in those experiments. The results show the promising results. So, the full scale experiment and full scale monitoring during actual service voyages were conducted and the lower fuel consumption was obtained for the condition with LFC surface. This paint seems to reduce the roughness effect in the water. Keyword: Ship Resistance, Lower Friction Paint, Surface Roughness, Towing tank Experiment

1. Introduction

Energy-saving technology is studied in various fields with the pressure from environmental protection and the unpredictable fuel price. In the field of ship building and operation, the energy-saving by reducing the ship resistance or high efficiency propulsion system have been investigated by many researchers, for example, the group discussion 3 in 25th ITTC[1]. In this study, the Lower Frictional paint (LFC) on ship surface is studied through rotational cylinder test, towing tank experiment, full scale experiment and full scale monitoring during actual service voyages. The paint is developed by Nippon Paint Marine Coating Co. Ltd. to get the lower frictional resistance than the conventional Self Polishing Copolymer(SPC).

In the rotational circular cylinder tests, LFC surface shows 5% lower frictional resistance than the conventional SPC for around 100μm.

In the towing tank experiment, three same geometry ship models which have different surface condition were tested. Two of them were painted with new LFC and Self-polishing paint (SPC), respectively. These two model have similar roughness(150μm). The remaining one was not painted and the FRP surface was polished to make the surface smooth (very low roughness). The resistance tests and velocity measurement in boundary layer were conducted. From the results of resistance test, total resistance coefficient of LFC surface model was about 6% lower than that of SPC surface model where fluid number was 0.25 to 0.4. And viscous resistance coefficient of LFC model was about 10% lower than that of SPC model where Reynolds number was 3.5 million to 5.5 million. From the velocity measurement, the axial velocity component in the boundary layer around new paint surface was larger than that around SPC surface. Therefore, roughness effect of LFC should be smaller than that of actual roughness. The simple consideration using White’s equation was done based on the measured results. In result, roughness effect of LFC on geometrical roughness of 153μm was

94

N. Yamamori, Y. Toda and Y. Yano

0.0030

0.0035

0.0040

0.0045

0.0050

0.0055

0.0060

0.0065

0.0070

1 6 11 16 21 26 31 36 41 46

Re

Ct

[x10 5]

従来型1

LFC1

従来型２従来型３

LFC2 LFC3

従来型４

0.0030

0.0035

0.0040

0.0045

0.0050

0.0055

0.0060

0.0065

0.0070

1 6 11 16 21 26 31 36 41 46

Re

Ct

[x10 5]

SPC１

LFC1

SPC２ SPC３

LFC2 LFC3

SPC４

0.0030

0.0035

0.0040

0.0045

0.0050

0.0055

0.0060

0.0065

0.0070

1 6 11 16 21 26 31 36 41 46

Re

Ct

[x10 5]

従来型1

LFC1

従来型２従来型３

LFC2 LFC3

従来型４

0.0030

0.0035

0.0040

0.0045

0.0050

0.0055

0.0060

0.0065

0.0070

1 6 11 16 21 26 31 36 41 46

Re

Ct

[x10 5]

SPC１

LFC1

SPC２ SPC３

LFC2 LFC3

SPC４

equivalent to that of 50μm. The full scale performance was estimated using equivalent roughness. The LFC seems to have the potential to reduce fuel by 5 % for 150μm roughness. The results of monitoring for actual ships and full scale experiment of ship resistance are also presented and the results show very promising feature.

2. Laboratory Experiment In the laboratory, the rotating cylinder test and resistance test using 3m model were carried out. The measurement of roughness was made by non-contact type roughness meter using laser displacement meter. The roughness of test cylinder surface was measured directly by special device. The roughness of the model surface was measured by measuring the replica surface taken from the model surface. 2.1 Rotating circular cylinder test

To measure the difference of frictional resistance acting in the paint surface, the rotational cylinder testing device was used to select the good paint. It is similar as the device used in Tanaka and Toda et. al[2] and the size of the cylinder is different and the devices have the similarity. The cylinder size is 10cm diameter and 10cm height. It was rotating in the 30cm diameter cylinder tank. The side surfaces of the cylinders were painted by several paints and top and bottom surfaces were treated as smooth surface. Before the tests using paint surfaces, the cylinders that have the artificial roughness similar as sand roughness were tested and the device was checked. The results show the test device can show the change of frictional resistance due to roughness.

The measurement device is shown Fig.1. The torque acting on the rotating cylinder was measured by subtracting the torque acting on the shaft and by the support bearings using the test without a cylinder (shaft only). The examples of results are shown in Fig.2. In the figure, the torque is non-dimensionalized using surface velocity and side surface area as shown in Eq.(1) and plotted versus Reynolds number Rn based on the circumferential length and surface velocity. Ct means frictional resistance coefficient or local skin friction coefficient.

2 2 2 2 51 12 2 4

t

Torque TorqueC

DnD D n D

2 2

n

n DR

(1)

where n: number of revolution of cylinder per second D:Diameter of circular cylinder

:density : kinematic viscosity

Fig.1 Experimental device for rotating cylinder. Fig.2 Example of test results. In Fig.2, frictional resistance with several LFC surface are compared with frictional resistance with

conventional SPC surface. Those surfaces have similar surface roughness around 90-100 m . Although those surface have the similar roughness, frictional resistance acting on the LFC surface clearly lower than that on SPC surface for all surface speed range. The frictional resistance acting on the smooth surface finished by buffing is lower than those results. To investigate the paint surface effect on the frictional resistance, the frictional resistance increase from smooth surface to paint surface is shown in Fig.3 at Rn=4,000,000 for LFC and SPC surface with various roughness.

95


Fig.3 frictional resistance increase due to paint surface versus surface roughness As shown in figure, the frictional resistance of LFC group is lower than that of SPC group. Usual

paint surface using usual painting device is 100-150 m , so LFC surface frictional resistance seems to be lower around 5% than usual SPC surface. LFC surface seems to reduce the effect of roughness.

2.2 Towing tank experiment

To measure the effect to the frictional resistance in the developing boundary layer due to painted surface, usual resistance tests using 3 m mathematical models were conducted in Osaka University towing tank (length: 100m, width: 8m, depth: 4.35m). The model geometry is shown by Eq.(2).

2 2

21 1 3.0 0.5 0.2

2

: distance from midship in lengthwise direction

: distance from center plane in lateraldirection

: distance from still water plane in depthwise direction

B z xy L m B m d m

d L

where x

y

z

(2)

The three FRP models were made from same mold and geometry of the models were checked before painting. The conventional SPC and present LFC chosen by rotating cylinder tests were painted on two model surface by same painting procedure, respectively. The roughness of conventional SPC surface and LFC surface were 160 m and 153 m , respectively. The other model surface was

finished by buffing to the hydrodynamically smooth surface (the roughness 11 m ). The surface roughness was the mean of the measured values on the replica surfaces taken from several model surface points. The photographs of the model are shown in Fig.4. After painting, the models were dipped into artificial seawater for three weeks and tested. Four resistance tests were conducted every one month and the painted models were dipped between the tests. Before the fresh water towing tank test, then models were washed by water. The test results for four tests were very similar, so the final test result is shown in this paper. As shown in top photographs, no turbulence stimulation device was installed on the model. The resistance test was conducted using usual two yawing guides, dynamometer (100N full scale) and towing rod as shown in the bottom photographs. The displacement weight (bare hull weight +ballast weight) of the models was kept to same value (1,306N) during experiment. The carriage speed U was changed from 0.4m/sec to 2.4m/sec. The example of resistance test result is shown in Fig.5. Fig.5(a) shows the measured resistance and (b) shows the total resistance coefficient. The resistance coefficient curve shows the laminar effect at low Froude number (Fn) and usual curve which has the large wave making resistance at high Fn. The resistance increase of the painted surface from the smooth surface due to the roughness is observed in the figure. But, the increase is clearly different between SPC surface and LFC surface. From the comparison between two painted surface, even in (a), the clear resistance reduction for LFC surface model from conventional SPC model resistance is observed in high speed range. From Fig.5 (b), the resistance reduction due to LFC paint compared with the model of SPC paint is seen in all speed range. The reduction is 4-5%. Although two painted models have similar roughness on their surface, the resistance of LFC model increases only 3-4% on the contrary that of SPC model is 8-10%.

96


(b)

Fig.4 Models for towing tank experiment and resistance test apparatus

Fig.5 Results of resistance tests To investigate the effect of paint surface to viscous resistance, usual analysis of resistance test was

done for hydrodynamically smooth surface model. Form factor K is estimated as 1.11 from low Fn data. Wave making resistance coefficient was estimated by subtracting viscous resistance (1+K)CF0

from CT total resistance coefficient. Frictional resistance coefficient CF0 of equivalent flat plate is calculated by Schonherr equation. For painted models, the viscous resistance coefficient is estimated by subtracting wave making resistance at same Fn from total resistance coefficient due to the same geometry. Fig.5 shows the total and resistance coeeficient for three models along with frictional resistance coefficient of the equivalent flat plate and wave making resistance. The viscous resistance coefficient of the painted models is larger than the smooth model due to roughness.

Fig.5 Resistance coefficient and ratio of resistance coefficient versus Reynolds number

02 10 0

2

3

2

0

0.2421 log ( )2

:Total resistance (N)

: Model length(m)

:Wetted surface area(m )

:Water density(Kg/m )

: cos (m /sec)

:

( ) (1 ) ( )

( ) (1 )

T n Fn F

T F W n

V

R ULC R C

R CU S

R

L

S

kinematic vis ity

K Form Factor

C smooth K C C F

C smooth K C

0 ( :determined at low )

(SPCor LFC) (SPCor LFC) ( )F n

V T W n

K F

C C C F

(a)

2

2

3

2

1

2

:Total resistance (N)

: Model length(m)

:Wetted surface area(m )

:Water density(Kg/m )

:gravity acceleration(m/sec )

T n

R UC F

LgU S

R

L

S

g

(a) (b)

97


The increase due to roughness on painted surface is smaller for LFC than for conventional SPC and the viscous resistance for LFC is smaller than for SPC. The ratio of resistance coefficient is also shown in Fig.5. From Fig.5(b), viscous resistance for LFC is lower around 10% than for SPC around Rn =3.5 to 5.5 million. The ratio of viscous resistance between two models increases as Rn increases, while the ratio of total resistance shows similar value for all Rn due to the ratio of viscous resistance and wave making resistance. From these results, LFC seems to have low equivalent hydrodynamic roughness.

To investigate this effect, the simple consideration using White’s equation [3] was done based on the measured results. In the equation, equivalent roughness height k is used. Frictional resistance coefficient increase 0FC of equivalent flat plate for a certain k was obtained by the total frictional

resistance coefficient calculated by same equation (k=0) from the total resistance coefficient calculated for a certain k. Viscous resistance of painted model was estimated by adding 0FC to viscous

resistance of smooth model. The result is shown in Fig.6.

Fig. 6 Prediction by White equation Fig.7 Full scale prediction Fig.8 Boundary layer profiles As shown if Fig.6, the prediction using k=160 m agrees well with experiment for SPC, on the

contrary the prediction using k=50 m agrees well with that for LFC. It means that LFC has the effect to reduce the roughness effect. In result, roughness effect of LFC on geometrical roughness of 153μm was equivalent to that of 50μm. The full scale viscous resistance for ship length 50 to 300m was predicted by assuming equivalent roughness 160 m and 50 m for SPC and LFC, respectively. The ship speed was assumed 15kt. Note that k/L decreases as ship length increases due to the constant k. Result is shown in Fig.7. Viscous resistance can be reduced by using LFC instead of SPC in case of painted rough surface(around 150 m roughness). If viscous resistance and wave making resistance are similar, the total resistance can be reduced about 5%. The reduction rate depends on hull form and Froude number (the ratio of wave making resistance and viscous resistance). The boundary layer measurement at 95% length position(x/L=0.95) was conducted for three models. The velocity profile shows that the velocity in boundary layer for LFC is higher than that for SPC. It also show that LFC reduce the roughness effect and momentum loss.

3. Deceleration test using training ship ‘Fukae Maru’ To investigate the effect of paint on the full scale ship, deceleration test using the training ship ‘Fukae Maru’ of Kobe University was conducted in 2006 and 2007 after docking. In 2006, LFC was painted on the former paint and conventional SPC was painted in 2007 in similar way. So, the roughness was similar for both experiments. The test was conducted for similar draft and inside the breakwater of Kobe port to minimize the wave, wind and tidal current effect as shown in Fig.9. The four tests were carried out for following wind, head wind, port side beam wind and starboard side beam wind case. CPP propeller is installed on the ship, so the experiment was done as following. The steady speed was accomplished at S/B Full Ahead Engine(CPP blade pitch angle 20degree) around 10knot for some

98


period and the pitch angle was changed to Stop Engine condition(pitch angle -1degree). After this change, the ship speed and position were recorded. Stop Engine condition means that the propeller does not produce the thrust at zero advance speed, so the propeller produce the drag force approximately proportional to U2. If the total resistance acting on hull is assumed to be constant around some speed, the total drag force including propeller and hull is proportional to U2. So, if the viscous resistance coefficient is smaller around 8kt, the period for deceleration from 8kt to 6kt is longer and the distance is longer. The example of ship speed time history is shown in Fig.10. From these time histories, the coefficient related to drag force is calculated by using the data between 8kt and 6kt and compared for two paint conditions. If this coefficient a is smaller, the drag force is smaller.

Fig. 9 Example of experimental route Fig.10 Example of ship speed time history Table 1 shows the analyzed coefficient a. The averaged values of a for LFC(No.4-10) and SPC(No.11-16) are 12.017 and 12.650, respectively. It means the total resistance of LFC surface is 5% lower than that of SPC surface. By monitoring the real operation from docking to docking for some Ferry and PCC, the fuel consumption per mile or hour was reduced by LFC. From those results, LFC seems to reduce the fuel consumption about 5% by reducing the roughness effect.

Table 1 analyzed coefficient related to drag

4. Conclusion

The viscous resistance of newly developed anti-fouling Lower Frictional paint (LFC-AF) was investigated through rotational cylinder test, towing tank model experiment, full scale experiment and full scale fuel consumption monitoring. In the laboratory experiment, the viscous resistance of LFC-AF is clearly lower than that of conventional Self Polishing Copolymer (SPC). LFC seems to have the effect to reduce the roughness effect of real geometrical roughness. In the full scale tests, the results shows LFC paint is very promising. References [1] Hubregtse A.(Chaiman), “Group Discussion 3: Global Warming and impact on ITTC Activities”,

Proc. of 25th ITTC, Vol.III, Fukuoka, Japan (2009). [2] Tanaka H., Toda Y. Higo K. Yamashita K ., “Influence of Surface Properties of Coatings to

Frictional Resistance”, Journal of Kansai Soc. Nav. Archi., Japan, No.239(2003) . [3] White F. M., “Viscous Fluid Flow : 2nd Edition”, McGraw-Hill, (1991).

99

1

親水性ペンキによる摩擦抵抗減す考察

資料３

摩擦抵抗低減に関する一考察

大阪大学

戸田保幸、眞田有吾、植原靖子

今回のものは委員会での話の中で出てきた部分的に高性能塗料を利用する等のことに対して検討したものであり、簡単な検料を利用する等のことに対して検討したものであり、簡単な検討を行った手始めで論文にまとめるほどのものではないと思わ

れるが1考察としてお話させていただく

• ISME2009のYamamori,Toda,Yanoの結果がベースでるのでそれを少し見ていただいた後今回の説明をさせていただく。

100

2

Ship Models

Wigley船L=3000mmB=500mmd=200mm排水量 33 3k f排水量=133.3kgf

図1 Plain (無塗装船)

図2 LFCN30 (親水性塗料)

図3 LFC46(自己研磨型塗料)

図１ LFCN30表面状態(粗度 153μm)

図２ LFC46表面状態(粗度 160μm)

粗度の影響を計算式で表すために、レプリカで計測された10点平均粗度の影響を計算式で表すため、リカで計測された点平均粗度高さRzを用いた。等価砂粗度との関係はこの程度の平均波長の場合1/2の高さの砂粗度となる。

101

3

実験時の摩擦抵抗推定法

山盛らではWhiteの近似式を用いて推定されてい山盛らではWhiteの近似式を用いて推定されていた。

今回はこれを直接運動量積分式を解くことによって高価な塗料を塗る位置などについても検討。より複雑な境界層内速度分布に対しても簡単に拡張可能（たとえば勝井らの摩擦抵抗式を求めた速度分布など）

①摩擦抵抗係数ＣFを、近似式ではなく運動量積分式を直接解いてもとめる

今回のアプローチ

分式を直接解いてもとめる。

②実船で考えた場合、親水性塗料にどれほど省エネルギ効果があるのかを調べるとともにエネルギー効果があるのかを調べるとともに一部に用いた場合の効果などについても検討

102

4

粗度を考慮した平板周りの境界層

運動量積分式 12 2 f

d cdx U

運動量厚さの定義

乱流境界層内の速度分布0

(1 )u u dyU U

*

dx U

*

2

*:

1 ln( ) 5.5*

u

UU

u u y Bu

Δ 　　

①Whiteの式

粗度関数ΔＢ

*1 ln(1 0 3 ) u kB k k

②CebeciらのNikuradseの粗度を考慮した式

2.25 01

k B

＜　　　

ln(1 0.3 )B k k

　　

12.25 90 ( 8.5 ln )sin(0.4258(ln 0.811))

190 ( 8.5 ln )

k B B k k

k B B k

＜　　　

　　　　

103

5

*

*

* *

1 1ln( ) 5.5 ln(1 0.3 )

1 1ln( ) ln( )

U u ku

U u u u y

0

1

0

1 20

2

(1 )

1 1(1 ln )( ln )

ln ( ln )

( 2 )

u u dyU U

d

d

　　　

*

*

ln( ) ln( )

1 ln

11 ln

11 ln

u

y

u u yU U

y

2( 2 )

　　　　　　　　　　　

*

*

*'

1 1ln( ) ' ' 5.5 -

1ln( ) ( ')

B

u B B B

u B

u e e

　　　

*

:

1 ln

u

U

'

*Be e

u

'2

1( 2 )BU e e

subroutine bibun(y,f,U)y: momentum thickness θ non-dimensionalｆ：ｄθ/dx nondimensional

real k,Rn,c,L,U,mk=0.4c=0.0001L=300.am=1.11am 1.11z0=0.02Rn=(U*L*1.e6)/am

do i=1,50 B=5.5-1/k*log(1+0.3*Rn*c/L*z0)z=k/(log(Rn*y/exp(-k*B)/(1/k-2*z0/k*k))

zsa=abs(z-z0)if(zsa.lt.1.e-12) thengo to 200elsez0=zendif

end do200 continue

f=z0*z0return

end

104

6

Rougness function ΔＢ

10

12

14

ΔB

‐2

0

2

4

6

8

0 100 200 300 400

ΔB ΔB=ln(1+0.3k)/κ

2.25 012.25 90 ( 8.5 ln )sin(0.4258(ln 0.811))

190 ( 8.5 ln )

k B

k B B k k

k B B k

＜　　　

＜　　　

　　　　

‐2k+

Momentum thickness

0 004 L=3m 0 0004 L=200m

0.001

0.002

0.003

0.004 k=160μm k=50μm plain

L 3m

運動

量厚

さ　

θ

0.0001

0.0002

0.0003

0.0004 L 200m

k=160μm k=50μm plain

運動

量厚

さ　

θ

61.0( / ) 1.11*10U m s 　　2 : Frictional ResistanceCoeffiF FC C

　　　L

0 1 2 3[106]

0

Rn0 1 2 3 4

[107]

0

Rn

105

7

Frictional Resistance

0.003

U*k=400*10 -6

U*k=800*10 -6

U*k=1200*10 -6

U*k=600*10 -6

U*k=1000*10 -6

U*k=1920*10 -6

U*k=2560*10 -6

U*k=3200*10 -6

U*k=3840*10 -6

0.002 k/L=1.0*10-6

k/L=0.5*10-66擦

抵抗

係数

CF

107 108 1090.001

k/L=0.25*10-6

plain

Rn

摩擦

実験の摩擦抵抗と計算値の比較

5

6 Cv (plain) 実験値Cv (k=160μm)実験値C (k 153 )

103CF

1

2

3

4実験値Cv (k=153μm)

計算値 CF（k=160μm) 計算値 CF(k=50μm) 計算値 CF(plain)

103ΔCF0

ΔCF0 (k=160μm)ΔCF0 (k=153μm)

ただし、Ｌ＝3m,動粘性係数 61.109256*10 Ｕ=0.4～2.4（m/s)

1 2 3 4 50Rn×10-6

ΔCF0 (k=160μm) ΔCF0 (k=50μm)

F0 ( μ )

106

8

速度ごとの実船の摩擦抵抗推定値

0 002

0.0025

0.003U=12knot

係数

　C

F

0.002

0.0025

0.003

U=8.0knot

抗係数　

CF

50 100 150 200 250 300 350 4000.001

0.0015

0.002

船長　L(m)

摩擦

抵抗

係

0.003

U=16.0knotCF

0.003

CF U=24.0knot

50 100 150 200 250 300 350 4000.0005

0.001

0.0015

船長　L(m)

摩擦抵抗

50 100 150 200 250 300 350 4000.001

0.0015

0.002

0.0025

船長　L(m)

摩擦

抵抗

係数

　

50 100 150 200 250 300 350 4000.001

0.0015

0.002

0.0025

船長　L(m)

摩擦抵抗係数

　C

ｋ=50,80,120,160,200μm

親水性塗料による摩擦抵抗値減少率

14.00

16.00実船レベルでのCF減少率

4 00

6.00

8.00

10.00

12.00

CF減

少率(%

)

U=8.0(knot)

U=12.0(knot)

U=16.0(knot)

U=20.0(knot)

U=24 0(knot)

0.00

2.00

4.00

50 150 250 350 450

船長L(m)

U=24.0(knot)

107

9

局部摩擦抵抗係数 fc

0 01f L=3m 0 006 L=200mf

0.002

0.004

0.006

0.008

0.01

部的

摩擦抵

抗係

数　

cf

k=160μm k=50μmplain 0.001

0.002

0.003

0.004

0.005

0.006 k=160μm k=50μm plain

部的摩

擦抵

抗係

数　

cf

61.0( / ) 1.11*10U m s 　　

104 105 106 1070

Ux/ν

局部 plain

106 107 1080

Ux/ν局

部

6.00E‐01

8.00E‐01

1.00E+00

1.20E+00

1.40E+00

抵抗

係数

ＣF

0.00E+00

2.00E‐01

4.00E‐01

1 2 3 4 5

摩擦

抵

①plain ②ks=50(μm) ③ks=160(μm) ④f:ks=50(μm)b:ks=160(μm)

⑤f:ks=160(μm)b:ks=50(μm)

108

10

0 0002

0.0004

0.0006

0.0008

0.001 ③k=160 ⑤back k=50 ④front k=50 ②k=50 ①plain

運動量厚

さ　θ

0 0.2 0.4 0.6 0.8 10

0.0002

x

0.0005

0.001 ③k=160 ⑨中央k=50 ⑥両端k=50 ⑧後方2/3 k=50 ⑦前方2/3 k=50 ②k=50 ①plain

運動

量厚

さ　θ

0 0.2 0.4 0.6 0.8 10

運

0.0025

抗係数　

cf

0 0.2 0.4 0.6 0.8 10.0015

0.002 ③k=160 ⑨中央k=50 ⑥両端k=50 ⑧後方2/3 k=50 ⑦前方2/3 k=50 ②k=50 ①plain

x

局部摩擦抵抗

109

11

ただしこれは平板での検討であるので船尾付近のガース長さの減少や逆圧力勾配による境界層の厚くなる部分では異境界層の厚くなる部分では異なると思われる。これについては粗度関数への圧力勾配影響も加味して積分型解法で検討予定

塗料の部分使用

摩擦抵抗が小さいと考えられる塗料の塗り方による違いは摩擦抵抗が小さいと考えられる塗料の塗り方による違いは、塗布領域以上の効果は見込めなかった。

摩擦が高い前半部に塗るのも後半部に塗るのも摩擦抵抗に違いはないという計算結果になった。

現在模型を5mとし検討中（次ページ）

110

１．

初めに

５ｍ数式模型船を用いて水槽実験により塗膜の抵抗特性を求めた。塗膜はかなり表面粗

度が大きいものをつくり模型船における計測でも大きな差が出るものを作成し調査したも

のである。

２．

塗装模型船を用いた水槽実験。

5m

のF

RP模型船を多数作成し、その表面をさまざまな粗度で塗装した（粗度１

2,3,4）

模型船

4隻を用意し抵抗試験を行った。これに加え表面が滑面である無塗装模型船も実験

した。また無塗装、粗度

1と

2については、抵抗の差と速度分布や乱れ度の大きさの変化

の差を比較するためステレオ

PIV

装置による流場計測も行ったが委員会では省略する。ま

た粗度１と２については表面粗度計を試作し表面形状の計測を行い、実際の幾何粗度計測

も行った。また、抵抗から等価砂祖度を推定し、実船推定の方法を提案した。以下それら

について示す。また

PIV

試験用に黒色に塗装した。

２．１模型船

模型船は表

1に示す主要目を持つ

Wigley

船型で船型を表す数式は表に入れている

表1 模型船主要目

22

2(1

()

)(1(

))

2:

::

x::

Bz

xy

dL

yB

d

zL

　各点の幅

全幅　

　喫水

　：長さ方向距離船体中心より

　　水面からの深さ

全長

模型船の写真を図１、図２に示す。図１が無塗装滑面模型船であり、

PIV

計測のため船尾

部分を艶消しブラックで薄く塗装し研磨して滑面とした。図２は今回作成した塗装表面を

持つ模型船の一例である。塗装模型船は全体の写真は同じように見えるので表面の写真を

図３に示す。

全長

5000mm

全幅

600mm

喫水

300mm

排水量

399.8kgf

全深さ

400mm

喫水

より

上部

は喫

水の

形を

その

ま

ま伸ばした垂直舷側

図１滑面模型船

図２塗装模型船の一例

図３各塗装模型船の表面

２．２抵抗試験

(a) 概要

大阪大学船舶海洋試験水槽

(長水槽

)において、抵抗試験を表２のような日程と水温の下で

実施した。模型船は外形は完全に仕上げられているが、

FR

Pの厚み等が異なるため模型船

重量

は異

なる

。そ

のた

め抵

抗試

験に

必要

な治

具を

取り

付け

たの

ち重

量を

測定

し、

排水

量が

同じ

にな

るよ

うに

バラ

スト

重量

を調

整し

た。

また

船体

に引

いた

喫水

線に

より

トリ

ムの

調整

は行った。トリム、シンケージのみフリーとしたので重心高さは厳密に調整していない。

表２

実験条件

実施日

使用した模型

船水

温(℃

)

9.12

PLAIN船

23.4

9.13

LFC(粗

度大)

23.4

9.14

LFC(粗

度小

),LFC(粗

度中)

23.2

9.15

SPC(粗

度中)

23.2

111

図4、図

5に示すように斜航軸

(曳航ロッド

)に検力計

(型式：

LM

C-3502-20)を

取り付

け、

それを模型船中央にピン接続し、各種船速

(0.4m/s～

2.8m/sまで

0.2m/s毎

)で曳航し、模型

船抵

抗(全

抵抗

値:R

t)を計

測し

た。

その

際に

、模

型船

が斜

航、

ロー

ルを

しな

いよ

うに

模型

船

の前後端付近にガイドを挿入した。

(b)実験結果

計測した全抵抗値

Rtを図６に示す。横軸をフルード数、縦軸を全抵抗値

Rtとする。

図６抵抗試験結果

図 4

抵抗試験の様子

図

5 斜航軸

(曳航ロッド

)

図に示すように明らかに粗度の影響が表れていることがわかる。粗度は番号が少ないほう

が粗い。見た目の粗度の大きいほどこの場合では抵抗が大きい。

抵抗を無次元化し全抵抗係数で示したものを図７に示す。図中の

PL

AIN

は滑面模型船を示

す。

図７全抵抗係数

全抵抗係数にするとより粗度による抵抗変化が顕著に見える。滑面とは粗度１で約１２％

の全抵抗の差がありかなり大きな差が生じている。抵抗は滑面より目視による粗度の大き

さの順に変化している。次に滑面模型船で通常の抵抗試験解析をおこない、形状影響係数

（低速で造波抵抗を０と仮定することにより０

.０５が得られた）と造波抵抗を求め、船型

が同じであるので造波抵抗を各フルード数で全抵抗からさし引くことにより、それぞれの

塗装面での粘性抵抗を求めた。これは計測値の引き算が入るためばらつきが大きくなるた

め全体の粘性抵抗傾向を見るために使用する。図８に粘性抵抗係数と滑面模型船の通常抵

抗試験解析より得られた造波抵抗係数を示す。粘性抵抗にすると同じ模型船租度であれば、

高速になるほど境界層が薄くなるため粗度の影響が出やすく差が大きくなる様子が見られ

る。これは理論的な考察から得られるものと

112

図８粘性抵抗係数

等しい傾向であるのでこの図から等価砂祖度を算出する。

（ｃ）砂粗度による粗度関数を仮定した計算との比較による等価砂粗度の算定

運

動量

積分

式は

二次

元の

圧力

勾配

のな

い平

板周

りの

流れ

を考

える

と運

動量

積分

式は

以下

のようになる．

2

12w

fd

cd

xU

::

:w

fU

c

運動

量厚

さ,

壁面

せん

断応

力,

:流

体の

密度

:一

様流

速,

局所

摩擦

抵抗

係数

ここで，運動量厚さの定義は

0

1u

udy

UU

:,

:u

主

流方

向の

流速

境界

層厚

さ

これを

x=0つまり平板全縁で運動量厚さθが

0となる条件で積分すると，

0

2

11

22

2

x

wF

dxx

Cx

Ux

:F

C平板摩擦抵抗係数

と

なる

．運

動量

厚さ

θを

定義

する

乱流

境界

層内

の速

度分

布が

わか

れば

，平

板摩

擦抵

抗係

数

FC

を算定することができる．

平板

の乱

流境

界層

内速

度分

布に

対し

て粗

度の

影響

を考

慮し

た乱

流境

界層

内の

速度

分布

を次

式で表わす．

*

*

1ln

5.5u

uy

Bu

*(/

):,

0.41:

:,

:w

u

y

摩擦

速度

カル

マン

定数

動粘

性係

数平

板表

面か

ら法

線方

向の

距離

ここで，

Bは粗度関数とよばれ，粗度の影響を含む項である．今回は

Wh

iteの式を

用いた．

Wh

iteの式を以下に示す．

*1

ln(10.3

)u

kB

kk

　　

　

:k

砂粗

度高

さ

これ

らを

用い

て、

模型

船の

抵抗

試験

範囲

のス

ピー

ドに

対し

等価

平板

の摩

擦抵

抗曲

線を

計算

した

。こ

れを

さま

ざま

な等

価砂

粗度

に対

して

示し

たも

のが

図９

であ

る。

図９

でも

実験

結果

の粘

性抵

抗と

同様

の傾

向を

示し

てい

る。

ただ

しこ

の計

算に

より

得ら

れる

滑面

の摩

擦抵

抗係

数は

若干

シェ

ーン

ヘル

の式

と値

が異

なる

ため

粗度

面と

滑面

の差

をシ

ェー

ンヘ

ルに

加え

たも

のを各粗度の摩擦抵抗係数としている。

以下，粗度

k(μm

)の摩擦抵抗係数，粘性抵抗係数をそれぞれ

()

FC

k，

()

VC

kと表わすこと

にする．

()

FC

kのグラフを以下に示す．粗度を

0μ

mから

200μ

mまで変化させて計算し

113

た．

図９摩擦抵抗係数

()

FC

k計算結果

図９

の摩

擦抵

抗係

数と

形状

影響

係数

を用

い粘

性抵

抗を

推定

した

もの

が、

計算

の粘

性抵

抗で

それ

を作

って

おき

実験

をプ

ロッ

トし

全体

で傾

向の

合よ

うに

等価

砂祖

度を

推定

した

。推

定の

ために実験値をのせたものを図

10に、推定した等価砂粗度による粘性抵抗計算値と実験を

図１０に示す。

図10

作成した図９に実験の粘性抵抗を表示したもの

図

10:実験値と等価砂粗度の曲線の比較

114

この

よう

に全

体の

傾向

が一

致す

るよ

うに

等価

粗度

を決

める

こと

で，

細か

い実

験誤

差は

除去

される．この計算結果と実験結果の比較により，水中では

LF

C粗度１が

100μ

m，粗度２

が50

μm，粗度３が

25μ

m，粗度４が

10μ

mの砂粗度と等価であることが確認できた．

この等価砂粗度を用いて実船の抵抗を推定する方法を考察する．

船の長さをさまざまに変えて同じフルード数で計算した、摩擦抵抗曲線を図

11に示す。

これ

によ

ると

実船

で差

があ

る粗

度で

あれ

ば模

型船

でも

差が

ある

こと

、ま

た模

型の

計測

精度

が高

いことを考

えれば実船

で有意な差

が生じる表

面粗度の影

響は

5m程度の模型船

で十分

同じ

フル

ード

数で

試験

する

こと

が可

能で

ある

とみ

るこ

とも

でき

る。

した

がっ

て今

回の

よう

な数

式船

型で

数多

くの

塗装

面に

対し

て等

価砂

祖度

を得

てお

けば

その

粗面

に対

する

実船

の摩

擦抵

抗、

ある

いは

粘性

抵抗

が推

定可

能で

ある

。通

常の

滑面

模型

船で

通常

の模

型試

験を

行い

形状影響係数

Kと各フルード数での造波抵抗係数がわかれば、図

11の対応する塗装面で対

応する長さの船の摩擦抵抗曲線を（１＋

K）倍し、それに造波抵抗を足すのが

1つの方法で

ある

が、

これ

まで

の相

関と

の関

係か

ら、

デザ

イン

スピ

ード

での

これ

まで

使用

して

きた

塗膜

と新しい塗膜のΔ

CF

の差を図

11から推定し通常の推定結果にそれをたしひきする方法も

考えられる。

図１１さまざまな船長に対する摩擦抵抗曲線

２．３粗度計測

粗度

１、

２に

つい

て粗

度を

計測

した

。こ

のた

めに

レー

ザー

距離

計と

トラ

バー

ス速

度を

用い

た計測装置を試作した。

図12

に今回試作した装置を示す。これにより実船塗膜なども計測可能と考えられるが、そ

れによるデータベース蓄積と公表は委員会では否定的であった。

計測

はレ

ーザ

の移

動速

度を

2.0mm

/s,移動

距離

を50.0m

m,デ

ータ

のサ

ンプ

リン

グ周

期を

1000μ

sに設定した。水槽実験を行った模型船の内、粗度１と粗度２２隻についてそれぞれ

船首

付近

、船

体中

央付

近、

船尾

付近

の三

点で

船の

深さ

方向

に変

位測

定を

行っ

た。

計測

の様

子を図１６に示す。得られた結果を図

17，

18に示す。これを用いて粗度を算出したものを

表３

に示

す。

等価

砂祖

度の

比率

とほ

ぼ同

じよ

うに

得ら

れて

おり

相関

があ

る。

また

以前

の塗

膜面

でも

実粗

度の

約半

分の

高さ

の等

価砂

粗度

が得

られ

てお

り同

じよ

うな

塗装

面で

あれ

ば実

粗度を計測すれば等価砂祖度を推定できる可能性もある。

表３粗度計測結果

図12

面粗度計測装置

115

Zp

1th

=R

p

Zp

2th

Zp

3th

Zp

4th

Zp

5th

Zv1

th=

Rv

Zv2

thZ

v3th

Zv4

thZ

v5th

lr

図１

3 計測

得ら

れた

全デ

ータ

を最

小二

乗法

で三

次多

項式

に近

似し

、求

めた

曲線

と各

デー

タの

最短

距離

を船体表面粗度として算出した。得られた船体表面粗度から

(6. 1),(6. 2)でそれぞれ定義され

る最大高さ粗さ、十点平均粗さを求めた。

ZP

VR

RR

ZR : 最

大高さ粗さ

基準長さにおける輪郭曲線の

山高さの最大値と谷深さの最大値との和

51

1(

)5

PJ

VJj

ZZ

ZJIS

ZJIS

R : 十

点平

均粗

さ

粗さ

曲線

で最

高の

山頂

から

高い

順に

５番

目ま

での

山高

さの

平均

と,

最深

の谷

底か

ら深

い順

に

５番

目ま

での

谷深

さの

平均

の和

R (a) 船首面粗度計測の様子

(b) 船体中央付近面粗度計測の様子

面粗度の基本パラメータ

X

ROUGHNESS, zero

10

20

30

4050

-0.1

-0.0

5 0

0.0

5

0.1

0.1

5

0.2

0.2

5

図１７表面形状計測結果

LF

C粗度大

図１８表面形状計測結果

LF

C粗度中

116

境界層でも差が出ていたので概略を示す。粗度１、粗度２、

PL

AIN

であればこの順に協会

層の厚さが大きい。乱れ強度もこの順に大きい。

y

z

-20

0-1

00

01

00

-35

0

-30

0

-25

0

-20

0

-15

0

-10

0

-50 0

Vx

10.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

図30P

lain 32

×32pixel

解析

y

z

-20

0-1

00

01

00

-35

0

-30

0

-25

0

-20

0

-15

0

-10

0

-50 0

Vx

10.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

図３０粗度１

32×

32pixel解析結果

y

z

-20

0-1

00

01

00

-35

0

-30

0

-25

0

-20

0

-15

0

-10

0

-50 0

Vx

10.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

図３２

:粗度２

32×

32pixel解析結果

0.3

0.40

.4

0.5

0.6

0.6

0.6

0.7

0.8

0.8

1

0.9

0.9

0.9

1

1

0.3

0.3

0.4

0.4

0.5

0.5

0.6

0.6

0.7

0.7

0.8

1

0.9

0.9

1

1

0.3

0.40.5

0.5

0.6

0.60.7

0.7

0.8

0.80.8

0.9

0.9

0.9

1

11

y

z

-200

-100

01

00

-350

-300

-250

-200

-150

-100

-50 0

図３３

:３隻の比較

(赤：粗度１，青：粗度２，黒：

PL

AIN

)

117

深江丸を用いての推力トルク計測

３．１概要

通常船舶では馬力は計測される場合が多いが、推力は計測されることは少ない。プロペ

ラ作動時の船体抵抗とプロペラ推力は釣り合うので、推力を計測すれば推力減少率の変化

が小さいと考えれば船体抵抗の増減がわかり、馬力はそのほかの影響、たとえばプロペラ

汚損による効率の低下（同じスラストを出すために必要なトルクの増加）が入っているた

め、それらを分離して船体の抵抗の変化のみを計測できる。したがって推力を計測するこ

とは大きな意味を持つ。計測手法は軸にゲージを張り付ける資料１の方法である。

３．２計測器の概要

神戸大学海事科学部の練習船深江丸がドックにおいて新しい塗料を塗装する前に深江丸

の中間シャフト（直径 145mm）にゲージを張り付けスラストトルクを計測した。装置の概

要図 36 に示す。図に示すようにシャフトに直接ゲージを張り、その出力をテレメータで送

信している。シャフト温度等も計測し温度の影響も考慮している図 37 に受信機側の表示を

示す。

図３６シャフト直貼りによるスラストトルク計測装置概要

図３７受信機とデータ取得用パソコン

資料５

118

3.3 計測結果

回転数 305rpm、可変ピッチ翼角 12，14，16，18 度において速力とスラストトルクの関係

を求めた。速度は深江丸の計測機によるものである。図 38 に推力、トルクの時系列を示す。

図３８推力馬力の時系列

同じ翼角で 2 回とっているが安定しており、速度が増加するときは、速度が上がる前は翼

角が大きくなると推力、馬力とも先に一度大きくなっていることがわかる。これなスピー

ドが小さく前進率が小さい部分で回っているためで、翼角を落とすときは逆の現象がみら

れる。この平均値を横軸に船速を取り書いたものが推力の図 39 と馬力の図４０である。

推力

(ton)

馬力

(PS)

時間(分）

119

図３９船速(kt)とスラスト(ton)の関係

同じ船速で見ると推力は下がっており、新しい塗料を塗った直後は大きく抵抗が下がって

いることがわかる。しかし同じ翼角では推力が同じで船速が大きくなった結果が出ている。

これは J の大きいところで同じ推力を出せることを意味し、揚力特性がよくなっているこ

とがわかる。これはプロペラの汚損による影響であると思われる。船速と馬力の関係を見

ると推力よりも大きく減少しており、プロペラの効率改善が大きいことがわかる。ドック

前には非常にプロペラが汚損していたものと思われる。

図４０船速と馬力（PS）の関係

スラスト

（ton）

船速（Kt）

馬力（PS）

船速(Kt)

120

419

Proceedings of 26th ITTC – Volume I

Specialist C

omm

ittee on Surface Treatm

ent Final report and recom

mendations to the 26

th ITTC

1.

Introduction

1.1.M

embership

R. A

nzböck, VM

B, A

ustria, (Chairm

an) M

. Leer-Andersen, SSPA

, Sweden,

(Secretary) M

. Atlar, N

ewcastle U

niversity, UK

J. H

. Jang, Samsung H

I, Korea,

H. K

ai, Yokoham

a National U

niversity, Japan E. C

arillo, CEH

IPAR

, Spain M

. Donnelly, N

SWC

CD

, USA

, left the com

mittee on 29-01-2010

1.2.M

eetings

The comm

ittee met 4 tim

es: N

ovember 24, 25, 2008, V

ienna M

ay 11, 12, 2009, Madrid

February 1, 2, 2010, Daejeon

October 28,29, 2010, G

othenburg 1.3.

Tasks

Below

we list the tasks given to the

comm

ittee by the 25th ITTC

1.

Review

state of the art of different surface treatm

ent methods

2.R

eview the possible im

pact on ship perform

ance in the following areas in

the light of the recent rapid developm

ent of coating systems:

a.)R

esistance (friction line) b.)

Propeller characteristics c.)

Cavitation behavior

d.)C

omfort (propeller induced

noise) e.)

Acoustic signature

3.R

eview the existing m

easurement

methods for surface roughness at

model-scale and at full-scale

4.Propose m

ethods that take into account surface roughness and other relevant characteristics of coating system

s in model testing.

a.)C

heck the need for changes to the existing extrapolation law

s b.)

Study the roughness allowance

for high-speed and conventional ships (hull, appendages and propellers)

420

Specialist Comm

ittee on Surface Treatment

TA

SK 1:

RE

VIE

W ST

AT

E O

F TH

E A

RT

OF D

IFFER

EN

T SU

RFA

CE

TR

EA

TM

EN

T

ME

TH

OD

S

The com

mittee

found practically

no support

from

paint m

anufacturers; except

brochures where they claim

reduction of fuel consum

ption up

to 10

%

neither reliable

measurem

ents nor serious data were provided

by the industry. In the following a short

overview over the products of several paint

manufacturers

given and

a few

essential

comm

ents are added to the single products. H

empel:

Hem

pasil X3

Type: Silicone Hydrogel, low

surface energy

Toxicity: low

toxicity, biocide free (V

OC

=Volatile organic com

pound)

Fouling: Self

cleaning from

8knots.

Silicon polymers form

a hydrogel microlayer

between the paint surface and the seaw

ater, resulting in enhanced antifouling capability, and im

proved self-cleaning potential. Service inter: 90m

onths

Friction: H

empel

does not

claim

reduction in frictional resistance per se, but claim

s reduced resistance due to less fouling. They

claim

4-8%

fuel savings

(see X

XX

XX

X). Tested at Force tow

ing tank, plates of about 1m

2. Have not obtained test

report.

121

421


HE

MPA

SIL 77500

Type: Silicone, w

ater repellent low

surface tension, second generation

Toxicity: biocide free

Fouling:Self cleaning above 8knots

Service inter: 40months

Friction:A

s seen below they claim

big im

provements in pow

er, however underlying

data must be investigated if possible. They

claim A

HR

of 20micron com

pared to 125-150 for convetional

Figure�1:�Com

pared�to�self�polishing�antifouling�

GL

OB

IC N

CT

Type:A

nti-fouling nanocapsule, Toxicity:

Cuprous oxide and other

biosides

Fouling:self polishing toxic anti fouling

self smoothing

Service inter:60months

Friction:self sm

oothing, exists in low

(deep seae) and high polishing (coastal)

OL

YM

PIC

Type:A

nti-fouling m

ineral fibres,

high mechanical strength

Toxicity: Low

level of VO

C

(400g/litres)

Fouling:self polishing toxic anti fouling

self smoothing

Service inter:?

Friction:self sm


(deep sea) and high polishing (coastal) O

CE

AN

IC

Type:A

nti-fouling m

ineral fibres,

medium

mechanical strength

Toxicity: Fouling:Service inter:36m

onth

Friction:self sm


(deep sea) and high polishing (coastal)

422

Specialist Comm


Com

parison of Hem

pel paints

Hem

pasil G

LO

BA

L N

CT

O

CE

AN

IC

OL

YM

PIC

Mechanical

Exellent Excellent

Very good

good Fuel saving

Exellent H

igh Fair

Neutral

Drydock inter

+60 60

60 36

Speed>13kn

0-35knot 10-30knot

10-25knot Self polishing

None

Excellent V

ery good good

VO

C275g/litre

400g/litre 430g/litre

450g/litre B

inderSilicon

Nanocapsule

Zinc carboxylateN

atural rasin B

iocide efficiency N

one H

igh M

edium

Fair IN

TE

RN

AT

ION

AL

INT

ER

SLE

EK

700

Type:Silicone

elastomer

fouling release, self cleaningToxicity:

None

Fouling:

Speed:15-30knots

Service inter:36month

Friction:C

laims

4%

fuel savings

compared to traditional SPC

. Average A

HR

100

INT

ER

SLE

EK

900 Type:

Fluropolymer fouling release, self

cleaningToxicity:

None

Fouling:H

ydrophobic w

aterreppelent surface, 40%

lower barnacle shear adhesion

strength than

intersleek 700.

Better

slime

repellent Speed:>10knots Service inter:36m

onth

Friction:C

laims

6%

fuel savings

compared to intersleek 700. A

verage AH

R 75

(Intersleek 700 AH

R=100, typical SPC

(Self Polishing

copolymer)=125m

icron. A

lso

claims

better efficiency

parameter

(wave

length). With below

method claim

ing 38%

lower C

f than intersleek 700

The following graphs, w

hich are copies of the

manufacturer’s

brochure, show

, w

hat “International”

claims

for their

products “Intersleak 700” and “Intersleak 900”. They prom

ise a reduction of the friction coefficient of 38%

without any proof; nevertheless a fuel

reduction of 6% is guaranteed ignoring the

type of ship, the Froude numbers and the ratio

of frictional resistance to total resistance.

122

423


IN

TE

RSW

IFT 655

Type:Self polishing copolym

er (SPC)

Toxicity: C

opper Acrylate biocide

release

Fouling:B

iocide releaseService inter:36m

onthFriction:

No info found

INT

ER

SMO

OT

H 746

Type:Self polishing copolym

er (SPC), low

er solvent em

ission Toxicity:

Copper A

crylate biocide release

Fouling:B

iocide releaseService inter:up to 60m

onthFriction:

No info found

INT

ER

SHIE

LD

163 INE

RT

A 160

Type:A

nti-corrosive, Ice resistant, no ice adhesion, high m

echanical strength, low

temperature

Toxicity: Low

VO

C (40g/litre)

Fouling:N

o anti fouling normally

Service inter:No inform

ation found Friction:

Claim

s 7-10% fuel saving

compared to traditional ani corrosive paint.

424

Specialist Comm


Com

parisons between International paints

Data taken from

http://ww

w.international-m

arine.com/Literature/H

RPC

_Folder_Paper.pdf ”Hull

roughness calculator”

Figure�2:�Savings�

123

425


Figure�3:�Fuel�increase�usage�(hybrid=�m

ix�of�CDP�and�SPC�(Interswift),�CDP=Controlled�D

epletion�Polymer�(Interspeed),�SPC=Self�

polishing�copolymer�(Intersm

ooth),�Foul�release�(Intersleek))�.�All�figures�have�same�description?�

JOT

UN

Very little inform

ation found

SEA

LIO

NType:

Foul release Silicone elastomer

Toxicity:

Fouling:

Service inter: Friction:

SeaQ

uantumType:

Self smoothing and self polishing

(SPC) H

ydrolising Toxicity:

Fouling:

Service inter:>60month

Friction:N

o information found

426

Specialist Comm


Paints�for�different�application�areas�Figure�1:�Typical�paint�system

s�for�different�application�

�Types�of�fouling��Several�thousand�species�of�m

arine�organisms�can�foul�the�surface�of�a�ship.�M

ost�will�stay�attach�or�

release�when�the�ship�speed�is�above�4�5knots.��W

hich�organisms�can�attach�is�affected�by�m

any�factors�such�as�pH,�tem

perature,�salinity,�dissolved�salts�and�oxygen�concentration.��Figure�2:�M

ain�Marine�fouling�orgasm

s�

�Type�of�antifouling�paints�in�second�half�of�20th�century�

�Allthough�these�paints�have�been�largely�phased�out�some�w

here�still�used�until�2001�where�IM

O�banned�the�

use�of�TBT�paints�worldw

ide,�because�of�their�toxic�effects�on�marine�life.�

�

124

427


TA

SK 2:

RE

VIE

W T

HE

POSSIB

LE

IMPA

CT

ON

SHIP PE

RFO

RM

AN

CE

IN T

HE

FO

LL

OW

ING

AR

EA

S IN T

HE

LIG

HT

OF T

HE

RE

CE

NT

RA

PID D

EV

EL

OPM

EN

T O

F C

OA

TIN

G SY

STE

MS

1.R

esistance (friction line) 2.

Propeller characteristics 3.

Cavitation behavior

4.C

omfort (propeller induced noise)

Task 2.1. Im

pact on the Resistance (friction line)

In the following an overview

over the recent papers concerning the impact of coating system

s on the resistance of a ship is given:

2.1.1.Ship resistance: R

esistance Data are published

M. P. Schultz, “Effects of coating roughness

and biofouling

on ship

resistance and

powering”,

Biofouling,

2007, Vol.

23, N

o.5, pp.331-341

Increased resistance of full-scale ship by surface

roughness is

calculated in

some

roughness conditions.

Calculation

methods

are based on model ship resistance results and

boundary layer similarity law

analysis. The calculation results show

increased resistance in heavy calcareous fouling is up to 86%

. V

alues of

shaft pow

er of

full-scale ship

obtained by trial data are given and compared

to calculation results. Both results agree w

ell w

ith each other. The resistance coefficient Ct

of typical

naval ship

is show

n in

Fig.1. H

owever, the data in this figure is N

OT so

reliable.

T Munk, M

Sc, “Fuel Conservation through

Managing H

ull Resistance”, M

otor ship Propulsion C

onference, Copenhagen A

pril 26

th, 2006

In this

paper, variations

of increased

resistance of some actual ships in service are

shown. The data show

s clearly the effect of dry-dock

and propeller

polishing. O

ne exam

ple show

s increase

of resistance

decreases over 20% thanks to dry-docking.

Another exam

ple shows increase of resistance

decreases about

10%

due to

propeller polishing.

We

can see

the increase

of resistance(%

) to days for developments.

K. Yokoi, “O

n the Influence of Ship's Bottom

Fouling

upon Speed

Performance”,

Toyama

National

College

of M

aritime

Technology, Bulletin of Toyam

a National

College

of M

aritime

Technology in

Japan2004

Speed trial data of training ship during past 8 years are show

n. Variations of Ship

speed, shaft horse power, fuel consum

ption are show

n in order to estimate the effect of

bottom fouling. The results show

shaft horse pow

er increases about 20% in full speed

condition because of fouling. Trial data are analyzed and variations of friction resistance are also show

n. We can see the shaft-horse

power and fuel consum

ption versus days after dock w

ith self-polish.

Leer-Andersen

M,

Larsson L,

“An

experimental/num

erical approach

for evaluating skin friction on full-scale ships w

ith surface

roughness”, J.

of M

arine Science and Technology Vol. 8, N

o1, 2003

The authors evaluate the increased skin friction

of full-scale

ships by

surface roughness.

CFD

code

“SHIPFLO

W”

is m

odified and velocity shift function is used in

428

Specialist Comm


order to take surface roughness effect into account. In order to determ

ine the velocity shift

function by

surface roughness,

experiment using long pipe in w

hich the wall

can be roughened is taken place. Full scale skin friction calculated by “SH

IPFLOW

” is show

n in Fig.14. We can not see any reliable

experiment data in this paper.

Lars-Erik Johansson, “The Local Effect of H

ull R

oughness on

Skin Friction.

Calculations B

ased on Floating Element

Data

and Three-dim

ensional B

oundary Layer

Theory”, R

ead in

London at

a m

eeting oh the Royal Institution of N

aval

Architects on A

pril 11, 1984

The effect of surface roughness on skin friction is calculated. The author takes place experim

ent using

floating elem

ent and

measure both skin friction and velocity profile

in boundary layer. Using those data obtained,

velocity shift is determined. A

boundary layer program

for

three-dimensional

turbulent boundary

layers is

employed.

Roughness

effect upon flat plate and two ship hulls are

presented. Increase in viscous resistance due to roughness from

painted surface of ship is show

n in Fig.14.

2.1.2.

Ship Resistance: R

esistance Data are not published

Y. Yano, N. W

akabayashi : “Presumption of

Bottom

Fouling in Real Ship”, J. of Japan

Institute of Navigation , 2008

The authors

attempted

to presum

e the

degree of bottom fouling of real ship by trial

test. They conducted short stopping test with

conventional paint and new type paint. From

experim

ental data, they obtained coefficient of stain. From

its value, the degree of bottom

fouling was assum

ed and the effect of paint w

as investigated.

Townsin R

L : “The ship hull fouling penalty”, International

Congress

on M

arine C

orrosion and Fouling No11, San D

iego, C

alifornia , 2003

Friction drag by slime and shell and w

eed are discussed. R

esearch history about them is

shown. M

ethods to measure the hard paint

roughness of

antifouling coatings

are sum

marized. The author refers to the relation

between surface roughness and skin friction.

Economic considerations are also m

ade.

J. Willsher : “The Effect of B

iocide Free Foul R

elease Systems on Vessel Perform

ance”, SH

IP EFFEN

CY,

1st International

Conference, H

amburg, O

ctober 8-9 , 2001

This paper firstly shows cause of hull

roughness. The

effect of

coating on

ship perform

ance is calculated by some form

ula. The effect of biocide free foul release coating to fuel saving is show

n. The author concludes foul

release products

give low

er hull

roughness than

biocidal A

F and

lower

environmental im

pact whereas higher initial

costs.

H. D

oi, O. K

ikuchi : “Frictional Resistance

Due to Surface R

oughness (1st Report) -

Effect on Reducing of Ship's speed by

Roughness

Models

–“, Journal

of the

Kansai Society of N

aval Architects, Japan,

No.194 , 1984

Five roughed plate which w

ere obtained in hull of real ships w

ere tested in the circulating w

ater channel

and m

easured frictional

resistance coefficient.

Speed decrease

estimated

by plate

frictional resistance

coefficient was 0.2 ~ 2 knot in case of blunt

ships, and 0.3 ~ 3 knot in case of high speed ships.

Y. Yam

azaki, H

. O

nogi, M

. N

akato, Y.

Him

eno, I.

Tanaka, T.

Suzuki :

“Resistance

Increase due

to Surface

Roughness (2nd R

eport)”, Journal of the

125

429


Society of

Naval

Architects

of Japan,

No.153 , 1984

Since hydrodynam

ic characteristics

of sand roughened surface and painted surface w

ere different in previous report, the author investigated

this problem

experim

entally using

simple

wavy

roughened surfaces.

Frictional resistance and velocity distribution in boundary layer w

ere measured in w

avy surfaces. R

oughness functions were obtained

by experimental results.

Y. Yam

azaki, H

. O

nogi, M

. N

akato, Y.

Him

eno, I.

Tanaka, T.

Suzuki :

“Resistance

Increase due

to Surface

Roughness (1st R

eport)”, Journal of the Society

of N

aval A

rchitects of

Japan, N

o..155 , 1983

The authors conducted experiments using

roughened pipes in order to measure frictional

resistance and

velocity distribution

in boundary layer. R

elation between roughness

height m

easured by

BSR

A

analyzer and

equivalent sand

roughness w

as obtained.

Velocity shift by surface roughness is used in

order to get resistance increase.

K.

Tokunaga, E.

Baba

:” A

pproximate

Calculation of Ship Frictional R

esistance Increase

due to

Surface R

oughness”, Journal of the Society of N

aval Architects

of Japan · No.152 , 1982

In order to calculate frictional resistance of a ship by surface roughness, the authors applied a-tw

o dimensional turbulent boundary

layer theory for rough surface to potential stream

lines over the hull surface. Potential stream

lines were calculated by H

ess-Smith

method. Increased resistance in full-scale ship

was calculated.

M. Sone : “Influence of the Fouled Ship

Bottom

on the Propulsion Horsepow

er of the Seikan Ferry-boats”, J. of the M

arine Engineering

Society in

Japan, Vol.16,

No.2 , 1981

Variations of Propulsion horsepow

er and fuel consum

ption of Seikan-Ferry boats were

investigated in 10 years using measurem

ent and

abstract log-book

data. This

ship is

docked every year and annual increase in delivered horse pow

er due to the ship bottom

fouling is about 8%. Since the paint w

as changed from

higher-toxic one to lower toxic

one, increase of propulsion horsepower seem

s to becom

e higher. H

. Orido, M

. Kakinum

a : “Speed Decrease

Due

to H

ull Surface

Roughness

(in Japanese)”,

Bulletin

of the

Society of

Naval A

rchitects of Japan · Vol.616 , 1980

The authors

showed

practical analysis

using data of some ships in service. R

elation betw

een surface roughness and ship age was

shown. Em

pirical approximate form

ula was

also shown in the graph and com

pared with

measured

data. H

owever,

the accuracy

of analysis seem

ed not to be high since the theory w

as not established enough.

2.1.3.R

esistance of Flat Plates

M.

Candries,

M.

Atlar

: “Experim

ental Investigation of the Turbulent B

oundary Layer of Surfaces C

oated With M

arine A

ntifoulings”, 2005

Velocity

distributions on

turbulent boundary layers on flat plates coated w

ith two

different new generation m

arine antifouling paints w

ere measured. The tw

o paints were

Foul R

elease paint

and Tin-free

SPC

respectively. Sm

ooth flat

plate and

plate covered w

ith sand grit were also used in order

to make sure the perform

ance of two new

paints.

Rem

arkable point

is that

LDV

430

Specialist Comm


measurem

ents for marine coatings have been

published in the open literature.

M.

P. Schultz

: “Frictional

resistance of

antifouling coating systems”, Journal of

fluids engineering, vol. 126, No.6, 2004

Frictional resistance

and velocity

distribution on several ship hull coatings in the unfouled, fouled, ad cleaned conditions w

ere m

easured. Test

surface coated

with

silicone, ablative copper, SPC copper and

SPC TB

T were used. The experim

ental results indicated

little difference

in frictional

resistance coefficient among the coatings in

the unfouled condition, however, after 287

days of marine exposure, test surface coated

with silicone show

ed the largest increases in frictional resistance coefficient.

M. P. Schultz :” The R

elationship Betw

een Frictional R

esistance and Roughness for

Surfaces Smoothed by Sanding”, Journal

of Fluids Engineering, Vol.124, 2002

The effect

of sanding

on surface

roughness w

as investigated.

The author

prepared 7 kinds of plates. One of them

was

not sanded and the others were sanded by

different fineness.

Plates w

ere tow

ed and

frictional resistance was m

easured in each case. The results show

ed resistance increase of unsanded plate against polished one w

as 5%

in average. Roughness function

U w

as show

n of all plates.

M. C

andries, M. A

tlar, A. G

uerrero and C.D

. A

nderson : “Lower frictional resistance

characteristics of Foul Release system

s”, Pro. of the 8th Int. Sym

p. on the PRA

DS,

Vol. 1, 2001

The roughness and drag characteristics of surface

painted w

ith SPC

(tin-free

Self-Polishing C

o-Polymer) and non-toxic Foul

Release w

ere investigated. Two plates coated

with these tw

o paints were tow

ed in tank and drag w

as measured. The results show

ed total

resistance of 6.3 m long plate coated w

ith Foul R

elease coating was 1.4%

lower on

average than

that coated

with

SPC.

Roughness functions of tw

o paintings were

shown.

Candries M

., Atlar, M

. and Anderson, C

.D. :”

Low-energy surfaces on high-speed craft”,

Proceedings HIPER

'01, Ham

burg, 2001

Towing test is carried out on three surface

conditions in

order to

compare

drag characteristics.

The surface

conditions are

Alum

inum, SPC

and Foul Release coating

respectively. From the experim

ental results, above R

eynolds number 2 * 10^7, it is show

n total

drag coefficient

of the

foul release

surface was on average 1.41%

lower than the

SPC surface.

M. P. Schultz : “Turbulent B

oundary Layers on Surfaces C

overed With Filam

entous A

lgae”, Journal of fluids engineering, Vol. 122, N

o.2, 2000

The effect of algae to frictional resistance w

as investigated. The surfaces covered with

filamentous algae w

ere prepared and put in a closed return w

ater tunnel. A tw

o-component

LDV

was used to obtain velocity distribution

in turbulent

boundary layer.

Significant increases in the skin friction coefficient for the algae-covered surfaces w

ere measured.

M. P. Schultz and G. W

. Swain : “The Effect

of B

iofilms

on Turbulent

Boundary

Layers”, Journal of fluids engineering, Vol. 121, N

o.1, 1999

Turbulent boundary layers over natural m

arine biofilms and a sm

ooth plate were

compared.

Profiles of

the m

ean and

turbulence velocity

components

were

measured. A

n average increase in the skin friction coefficient w

as 33 to 187 % on the

fouled specim

ens. The

skin friction

coefficient was found to be dependent on both

biofilm thickness and shape of surface.

126

431


2.1.4.R

esistance of Circular C

ylinders

S.M. M

irabedini, S. Pazoki, M. Esfandeh, M

. M

ohseni, Z. Akbari : “C

omparison of drag

characteristics of

self-polishing co-

polymers

and silicone

foul release

coatings: A

study

of w

ettability and

surface roughness”, Progress in organic coatings, Vol. 57, N

o.4, 2006

Drag on som

e surfaces coated with som

e paints is m

easured using a smooth alum

inum

cylinder connected

to a

rotor device.

Dow

nward shift of the velocity distributions

and frictional resistance coefficients for each test cylinder by R

eynolds number are also

measured.

The drag

characteristics of

a surface are affected by its free energy and roughness param

eters.

Weinell C

E, Olsen K

N, C

hristoffersen MW

, et al.

: “Experim

ental study

of drag

resistance using a laboratory scale rotary set-up”,

Biofouling,

International C

ongress on

Marine

Corrosion

and Fouling

No11,

San D

iego, C

alifornia, 2003

A laboratory scale rotary set-up w

as used to m

easure the drag resistance, and the surface roughness

of the

samples

was

measured.

Measurem

ents on

pure paint

systems

and m

easurements

on large-scale

irregularities w

ere investigated. The contribution from a

modern self-polishing antifouling or silicone

based fouling-release

paint w

as negligible

compared to the one from

irregularities of hull of ship.

Hisao TA

NA

KA

, Yasuyuki TOD

A, K

iyoaki H

IGO

, K

azuharu YA

MA

SHITA

:

“Influence of

Surface Properties

of C

oatings to Frictional Resistance”, ournal

of the Kansai Society of N

aval Architects,

Vol.239, Japan, 2003

In order to investigate effect of surface properties of coatings to frictional resistance, experim

ents were carried out using a rotating

cylinder type

dynamom

eter built

by the

authors. Frictional

resistance and

velocity distribution

in turbulent

boundary w

ere m

easured. The

aging effect

of paints

on surface roughness w

as shown.

2.1.5.Interaction Ship and Propeller

M. M

iyamoto :” Estim

ation and Evaluation of Ship Perform

ance in Actual Seas - R

eview

and Evaluation of Fouling, Aging Effect

and Sea Condition-“, Journal of the Japan

Society of Naval A

rchitects and Ocean

Engineers, Vol.4 2007

The author estimates the effect of fouling,

aging effect and sea condition upon real ships. The approxim

ate method exploited by the

author is

verified by

comparing

with

measured data and data of abstract log-book.

As a result, it is show

n that the accuracy seem

s to

be quantitatively

practical. The

approximate

method

could be

applied to

design stage.

A. M

atsuyama, T. N

ishiya, T. Araki , T.

Imada

:” Studies

on Propulsive

Performance by M

arine Fouling of Ship-hull and Propeller”, B

ulletin of the Faculty of Fisheries, N

agasaki University N

o.83, 2001

In order to investigate the effect of marine

fouling on ship hull and propeller, the author analyzed the log-book data from

1990 to 1998. Shaft

horse pow

er, am

ount of

fuel consum

ption, admiralty coefficient and ship

speed were investigated. It w

as recognized that fuel consum

ption increases up to 22%

from the value of 1990.

432

Specialist Comm


K.

Nagatom

o, H

. M

atsushita, E.

Inui, Y.

Miyoshi : “Studies on M

arine Fouling of the B

ottom Plates and Propeller Surface –

1”, The Journal of Shimonoseki U

niv. of Fisheries, Vol.41, N

o.4, 1993

Bottom

and propeller fouling of real ship w

as investigated through one year. It was

known the kind of m

arine fouling organisms

and process

of attachm

ent. The

effect of

marine fouling prevention by pouring sea

water w

ith dissolved innoxious copper-ion w

hich was supplied by the system

into the dom

e of bow-thruster w

as also investigated.

K. Sato, K

. Inoue, E. Takeda, H. A

kizawa, Y.

Mine,

Y. K

oike, Y.

Miyazaki

: “Experim

ental Study

of Prevention

of B

ottom

and Propeller

Foulings w

ith R

egard to

Energy Saving

of Fishing

Boats”,

Journal of

Tokyo U

niv. of

Fisheries, Vol.74, No.2, 1987

In order to investigate the effect of marine

antifouling paints on propulsion performance

of actual ships, firstly some test plates coated

with som

e paints were put in seaw

ater and perform

ance of paints was studied. Secondly,

speed trial tests were taken place. V

ariations of

BH

P and

surface roughness

just after

painting, before docking, and after docking w

ere shown.

E. Nishikaw

a, M. U

chida :” On Propulsion

Property of

FUK

AE

MA

RU

Equipped

CPP and its D

eterioration due to Surface Fouling”, B

ulletin of Kobe M

archant Ship U

niversity Vol.33, 1985

The effect

of surface

fouling on

the propeller and ship w

ere investigated. Trial sea data of training ship equipped w

ith CPP w

ere obtained just before docking and just after docking

in 3

years. Perform

ances of

propulsion property with and w

ithout fouling w

ere compared. The results show

ed change of propulsion

performance

with

CPP

was

different from the one w

ith FPP.

N. N

akai, S. Suzuki : “On the Presum

ption of B

ottom's R

oughness with M

aking Use of

Propeller Efficiency on CPP”, B

ulletin of K

obe Marchant Ship U

niversity Vol.32, Japan, 1984

In order to estimate the bottom

fouling of real ship, practical m

ethod was presented. The

speed trial test was taken place before and

after docking. Surface roughness in fouled condition w

as estimated by the increase of


using B

owden

formulation. The results show

ed after docking, surface roughness becam

e about 6.2 mm

from

145m

in cleaned condition.

N. N

akai, S. Suzuki : “The Effect of Marine

Fouling -O

n the

Result

of A

ctual Experim

ents with the Ship Installed C

PP-“, J. of Japan Institute of N

avigation, 1983

The increased

resistance caused

by adhesion

of barnacle

to propeller

was

calculated. Firstly, the situation of foul of propeller w

as measured. The m

easurement

results showed barnacle adhered near trailing

edge near boss. Barnacles w

ere approximated

as a half-cylinder solid and loss-horse power

was

calculated. The

calculation results

showed loss horse pow

er was over 1%

.

N. N

akai, S. Suzuki : “On the Effect for

Propelling Performance in C

onsequence of

Marine

Fouling and

the Practical

Method

of Presum

ption of

Bottom

's R

oughness on

FUK

AE

MA

RU

before

Autum

nal D

ocking”, B

ulletin of

Kobe

Marchant Ship U

niversity Vol.32, Japan , 1983

The foul

condition on

bottom

and propeller

of real

ship w

as investigated.

Because of long-tim

e mooring during A

ugust to O

ctober, fouling was progressed so m

uch. A

ccording to speed trial, ship speed became

about 70% com

pared to cleaned condition. The cause of speed decrease cam

e from ship

hull fouling by two-third; the rest cam

e from

propeller fouling.

127

433


2.1.6.

Further Papers of possible Interest

2.1.6.1.Paint

Elisabete A

lmeida,

Teresa C

. D

iamantino,

Orlando de Sousa :” M

arine paints: The particular case of antifouling paints”, 2007

The authors presented a general overview

of m

arine antifouling

paints. Firstly,

interaction between ship hull and sea w

ater w

as explained. Marine organism

s that adhere to ship hull w

ere shown. The history of the

development of antifouling technology w

as explained. A

s a next generation marine paints,

more

environment

and m

an-friendly antifouling paints, such as C

DPs, TF-SPC

s and B

iocide-free paints were show

n.

Cham

bers LD, Stokes K

R, W

alsh FC, et al. :

“Modern approaches to m

arine antifouling coatings”, 2006

This article reviews the developm

ent of m

arine antifouling

coatings. H

istoric antifouling m

ethods were show

n. Over 100

papers were review

in it. Am

ong them, 10

major

paper w

ere chosen

and introduced.

Performances of som

e coatings are compared.

Tin-free self-polishing copolymer (SPC

) and foul

release technologies

are current

applications however m

any alternatives have been suggested.

Casse F, Sw

ain GW

: “The development of

microfouling

on four

comm

ercial antifouling

coatings under

static and

dynamic im

mersion”, 2006

Four test panels coated with paints w

ere im

mersed in seaw

ater in order to compare

their performance against m

icrofouling under static and dynam

ic imm

ersion. Three paints w

ere biocide based (tributylin self-polishing, copper self-polishing, copper ablative) and one w

as biocide free (silicone fouling release). It w

as know that total bacteria counts w

ere

similar on all coatings after static im

mersion,

but after

dynamic

imm

ersion the

largest decrease in num

bers was seen on the fouling

release coating.

Tetsuya SEND

A : “Ship B

ottom A

nti Fouling C

oating and

Marine

Environment

(in Japanese)”, 2006

History

of developm

ent of

anti-fouling coating

is sum

marized.

Since restrictions

against toxic coating have become harder in

recent years in terms of protection of m

arine environm

ent, the

author evaluates

the environm

ental risk for anti-fouling coating. The author says it is necessary to establish the w

ay to

evaluate properly

environmental

effects of anti-fouling substances, and to find som

e low-risk substances.

Anderson,

C.D

., A

tlar, M

., C

andries, C

., C

allow, M.E., M

ilne, A. and Tow

nsin, R

.J : “The development of Foul R

elease coatings for seagoing vessels”, 2004

This paper

describes the

history of

development

of antifouling

paint. Firstly,

some m

arine fouling organisms are explained.

Secondly, some explanation about antifouling

painting is done. The method how

fluid drag on

foul-release coating

is calculated

is explained. Lastly, perform

ance of antifouling coating is show

n. Reading this paper, reader

can get the overall knowledge of antifouling

painting.

Kazuya O

GAW

A : “The Prevention of M

arine Fouling on FR

P Ship Hull by C

oating a N

on-polluting and Anti-fouling Paint 2 -

Relation

between

Preventative Perform

ance and Physical Properties of Silicone C

oated Film-“, 1996

434

Specialist Comm


In the

second report,

the author

investigates the reason why the proposed new

coating m

ethod has an effectiveness for the prevention of bio-foulings on FR

P ship hulls. The physical properties of the coated film

are investigated. The author m

easures a contact angle and a sliding angle of a drop of w

ater on the silicone coated film

. The author also observes the repelling appearance of colored w

ater sprayer on this film.

Kazuya O

GAW

A : “The Prevention of M

arine Fouling on FR

P Ship Hull by C

oating a N

on-polluting and Anti-fouling Paint 1 -

Effectiveness of

Silicone C

oated Film

against M

arine fouling-“, 1996

In the first report, the author develops new

coating method by using a nontoxic paint

instead of toxic paints. FRP test plane w

ith som

e coating are put in sea for several month

and antifouling performance are com

pared w

ith each other. The paint which show

s the best antifouling perform

ance is painted to real ship and its perform

ance is confirmed.

Nobuyoshi

HIR

OTA

:

“Non-Toxic

Anti

Fouling C

oating w

ithout A

dhesion of

Marine C

reatures (in Japanese)”, 1985

Developm

ent and application of non-toxic anti

fouling coating

called “B

ioclean” developed by C

HU

GO

KU

MA

RIN

E PAIN

TS LTD

is explained. In case of the application to the propeller of the 200 thousand D

W ore

carrier, it is reported that no adhesion of m

arine creatures occurred in half year after launching. In case of the application to the propeller

of the

support ship

of national

defense m

inistry, it

is reported

that no

adhesion of marine creatures occurred in one

year.

2.1.6.2.M

arine Creature

Schultz M

P, K

avanagh C

J, Sw

ain G

W

: “H

ydrodynamic

forces on

barnacles: Im

plications on detachment from

fouling-release surfaces”, 1999

In this

paper, lift

and drag

acting on

barnacles were m

easured. The results were

compared

to the

results obtained

by

hemisphere,

cube and

pyramid.

Lift coefficient rem

ained nearly constant over the range of R

eynolds numbers tested, how

ever drag

coefficient decreased

slightly w

ith increasing R

eynolds number.

A table of the literature checked for task

2a is attached in appendix 1 to this report.

TA

SK 2.2: IM

PAC

T O

F PRO

PEL

LE

R C

OA

TIN

G SY

STE

MS O

N PR

OPE

LL

ER

C

HA

RA

CT

ER

ISTIC

S

2.2.1.Introduction

This section

gives a

background on

propeller coating systems and their influence

on propeller characteristics. In item 2.2.2. the

important

aspect of

the propeller

surface m

easurements

and representation

are review

ed. This is followed by 2.2.3. w

here the

review of reasons and associated different

coating m

ethods reported

in the

open literature are given. B

ased on this review

since the Foul Release (FR

) coating systems

have been developing as the prime propeller

coating system, in 2.2.4 a brief background to

this coating system is given w

ith a view to the

128

435


propeller coating. Item 2.2.5. presents the

recent applications and review of the effect of

the FR coatings on the efficiency, cavitation

and underwater acoustics of propellers as w

ell as the interaction of this coating system

with

bio-fouling. Finally,

2.2.6. presents

the concluding

remarks

from

the review

and

recomm

endations for

further research

on propeller coating.

When the loss in ship perform

ance is associated w

ith the condition of the ship hull, the effect of the propeller surface condition is often overlooked. M

osaad (1986) stated that in absolute term

s, the effect of the propeller surface condition is less im

portant than the hull

condition, but

significantly m

ore im

portant in terms of energy loss per unit area.

In economic term

s, high return of a relatively cheap investm

ent can be obtained by propeller m

aintenance. This has been well recognised

by cautious

ship operators

who

regularly polish the propellers of their vessels. W

hile this is a good practice, the inconvenience of finding suitable tim

e and place as well as the

associated cost

favour for

the alternative

means of keeping propellers clean by coating,

especially after the recent introduction of Foul R

elease (FR) type coating. B

esides, there has alw

ays been an interest to the coating of propellers to avoid or reduce fouling grow

th and galvanic corrosion of ship hull and as w

ell as to resist to cavitation erosion if it is ever possible.

Propeller coating applications have been grow

ing with increasing applications of foul

release (FR) coatings on ship hulls during the

last fifteen years or so, especially on the propellers of large cargo vessels. A

ccording to the data base of one of the m

ajor coating m

anufacturers, the current breakdown of the

ship antifouling applications, about a 5% of

their hull coating applications is with the FR

type

and this

ratio has

been increasing

considerably due to environmental scrutiny

and competitions am

ongst newly em

erging other FR

brands. This type of coating is favoured for the propeller applications due to

their sm

oother finish

and im

proved application as w

ell as longevity relative to the Self-Polishing

Copolym

er (SPC

) types.

In fact

some

paint m

anufacturers have

been offering free of charge paint applications to ship ow

ners who are w

illing to paint their vessels by FR

coating. Again, according to

the data base of the above mentioned m

ajor paint m

anufacturer the number of the coated

propellers has

reached to

more

than 250

during the last 10 years.

The main objective of propeller coating is

to control

fouling grow

th beside

other potential

benefits in

association w

ith im

proved condition

of the

blade surfaces

including propeller efficiency, cavitation and noise.

How

ever prior

to exploring

these effects,

one needs

to clarify

differences am

ongst surface

deterioration and

fouling. Surface

deterioration m

ay be

caused by

corrosion, im

pingement

attack, cavitation

erosion or

improper

maintenance

whilst

fouling is mainly due to m

arine growth of the

animal type, acorn barnacles and tubew

orms

as well as the slim

e type, Atlar et al (2002).

Depending upon its extent w

hile the surface deterioration can be represented by surface roughness the representation of fouling is rather com

plex and hence its effect upon the propeller is difficult to quantify since very little theoretical and experim

ental work done

on the subject. How

ever it is a well-know

n fact that, w

hether it is a surface deterioration or fouling, any m

icro or macro level change

in the

blades surfaces

will

increase the

propeller loss due to the viscous friction effect in addition to the potential axial and rotational losses. The frictional loss can be as high as 15%

of the total propeller losses depending upon

the propeller’s

loading condition,

Glover (1991). It is therefore beneficial to

keep the propeller surface free from m

arine fouling and as sm

ooth as possible to reduce the frictional loss beside other consequences of these causes that m

ay lead onto undesirable earlier inception and further developm

ent of cavitation as w

ell as increased underwater

noise.

436

Specialist Comm


2.2.2.M

easurement and representation of propeller surface condition

Before the effects of roughness upon the

performance of a propeller can be quantified

the roughness

of the

surface has

to be

measured.

There are

various m

ethods for

doing this,

such as

using a

propeller roughness com

parator, by using a portable stylus instrum

ent or by taking a replica of the surface of the blades and m

easuring it with

laboratory equipm

ent such

as optical

measurem

ent systems. A

detailed description of both the stylus (by m

echanical contact with

the surface) and optical measurem

ent systems

can be found in e.g. Thom

as (1999). On the

other hand

the propeller

roughness com

parator is a simple gauge by w

hich the roughness of a propeller can be com

pared to a surface of know

n roughness. The most w

ell-know

n example of this is the R

ubert propeller roughness com

parator. The gauge consists of six exam

ples (A, B

, C, D

, E and F) of surface finish that range from

an average meanline

roughness am

plitude R

a =

0.65μm

to an

amplitude of R

a = 29.9μm, see, e.g. C

arlton(2008). The exam

ples represent the surfaces of actual uncoated propeller blades. Exam

ples A

and B represent the surface roughness of

new or reconditioned propeller blades w

hile the rem

aining examples are replicas of surface

roughness taken from propellers eroded by

periods of service. C, D

, E and F can be used to assess and report upon the propeller blade surface condition after periods of service.

The measurem

ent of propeller roughness, w

hichever method is used, presents a num

ber of problem

s which are sim

ilar problems to

those of measuring hull roughness. They stem

from

the

very nature

of propeller

blade roughness, w

ith its wide variety of am

plitudes, textures and locations. T

ownsin et al (1981)

discussed the

propeller roughness

measurem

ent problem

s and

concluded the

following: any one sm

all area of a blade will

give a wide range of values for all roughness

parameters; therefore for any point on the

blade, an average of many sam

ples is needed to

reach a

representative figure.

How

ever these values of average roughness w

ill vary hugely over the blades surface, m

eaning that the roughness needs to be m

easured at many

locations. This is important as the sam

e level of roughness w

ill cause very different effects on section drag, depending upon w

here on the blade it is located. Fouling and dam

age, such as galvanic or cavitation erosion, can have a m

assive effect upon the roughness measured

and hence the section drag. Most im

portantly, there w

as no agreed standard methodology for

measuring

roughness, no

matter

how

arbitrarily defined.

In an

attempt

to establish

a standard

methodology

for the

propeller roughness

measurem

ents T

ownsin

et al.

(1985) proposed the follow

ing procedure: each blade surface is divided into a num

ber of roughly uniform

radial strips, for each of which 3

measurem

ents w

ere taken

with

a cut-off

length of

2.5mm

. A

t that

time

this w

as designed

for use

a stylus

type roughness

device, the Surtronic 3 instrument, so R

a (the m

ean line average roughness amplitude) and

Pc (the Peak Count per unit length, w

hich is a texture param

eter) were recorded for later

conversion into

Musker’s

“Apparent”

or “C

haracteristic” roughness parameter, h’, by

the approximation below

. C

aP

Rh

)5.2

(0147

.0'

2�

This was then used to calculate a value for

the Average Propeller R

oughness (APR

). This is a w

eighted average, so the roughness closer to the tip has a m

uch greater influence than the sam

e roughness would, if placed nearer

the blade root. Five sections were suggested

and given the weights show

n in Table 1.

Table 1. Weights suggested for calculating

APR

, based on 5 sections.

129

437


iRegion

Weight

10.2��0.5

0.072

0.5��0.70.22

30.7��0.8

0.214

0.8��0.90.27

50.9��tip

0.23

By assum

ing h’ is constant within each

weighting band; A

PR for the 5 bands is given

by, 3

51

3 1)'

(��

��

ii

hW

APR

A

more

generalized form

for

APR

, suitable

if a

survey of

the entire

blade roughness is not available (the m

issing values should not just be assum

ed to be zero) is given by

5)'

(3

3 1

��

� � � ��

� � � ��

n

mW h

WAPR

nmi

nmi

i

The weights are evaluated such that for a

uniform distribution of roughness, A

PR = h’.

In the above procedure “characteristic” roughness param

eter h’ was obtained from

a drag-roughness

correlation w

ith replicated

coated surfaces based on Mosaad’s (1986)

extensive measurem

ents. This parameter w

as originally proposed by M

usker (1977) to

characterize a surface by a single parameter

taking both the amplitude and texture of the

roughness into account. At this point it m

ust be noted that a single param

eter (such as average roughness height) as those m

easured by

Broersm

a and

Tasseron

(1967)or

equivalent sand roughness height (ks ) of the

fully turbulent frictional drag expression for the

propeller blade

surfaces in

ITTC’78

procedure, w

ill not

be suitable

for representing

the effect

of coatings

on propellers. This is not only on the ground that this expression is based on the N

ikuradse approach

of sand

roughness, since

actual propeller roughness is different than the sand roughness,

but also

on the

ground of

neglecting the

effect of

surface texture.

Although a surface m

ay have relatively large average roughness am

plitude its texture may

have a long wave length sinusoidal texture.

This type of surface may cause low

er drag w

hen compared to a surface consisting of

smaller am

plitudes but with a jagged texture

consisting of

closely packed

sharp peaks

surface as claimed by G

rigson (1982). This claim

was further proved by C

andries (2001) through com

prehensive boundary layer, drag and roughness m

easurements and analysis of

flat plates coated with tw

o different marine

coatings which w

ere a comm

ercial FR and a

tin free Self-Polishing Copolym

er (SPC) type.

In this study it was show

n that the FR coated

system belonged to the form

er surface type w

hile the SPC coated surface belonged to the

second type suggested by Grigson as typified

in their comparative roughness profiles show

n in Figure 1. It can be seen that w

hen long-w

avelength waviness, w

hich is unlikely to have any effect upon the drag, has been filtered out, tw

o striking features appear: not only are the am

plitude parameters (i.e. R

a, Rq,

Rt) of the FR

profiles typically lower, the

texture parameter of the surface, w

hich is represented by the slope (Sa), is significantly low

er. In

metrological

terms

this type

of texture

is know

n as

“open” w

hereas the

spikier texture of a tin-free SPC surface is

known as “closed”.

438

Specialist Comm


Foul Release R

oughness profile:R

a = 1.10R

q = 1.21R

t = 4.50Sk = -0.87Ku = 5.04Sa = 0.33

-15

-10 -5 0 5 10 15 20

05

1015

2025

3035

4045

50

mm

micron

Figure 1 – C

haracteristics of a typical foul release (Intersleek 700 – on the left) and tin-free SPC (Ecoloflex – on the right) roughness profiles taken by

laser profilometry, C

andries et al (2001).

As it is noted in the above review

, an accurate representation of blades surfaces by characteristic

roughness param

eter requires

relatively sophisticated measurem

ent devices for proper analysis of the surfaces. These devices

are preferred

to be

optical and

portable as well as practical that can be used

in dry docks etc. Unfortunately such system

s currently are not available although there are increased activities in this field especially after the introduction of the FR

coatings. As

discussed earlier these coatings do not readily allow

themselves to be m

easured by practical stylus

type devices

although they

are currently being used on based on certain skills involving

some

errors in

measurem

ents. A

lthough taking

replica (print)

from

the actual blade surfaces is relatively direct and hence

more

accurate w

ay m

easurement

method, it is rather im

practical and it has its

own

problems.

At

this point,

until such

devices are available, it is plausible to think of establishing a new

comparator system

, which

is based on a similar idea to the R

ubert com

parator. How

ever this new com

parator can

be developed

for foul

release coated

sample surfaces w

hich are graded based on different paint applications varying from

good to

bad since

the application

grade is

an im

portant param

eter in

the texture

and roughness

parameters

for new

ly applied

coatings. Of course these sam

ples will be

indirect and will not necessarily represent the

actual coated blades after a period in service. H

owever, as long as they are not dam

aged, FR

coating

systems

can m

aintain they

roughness and texture characteristics similar

to the new condition except the effect of slim

e. There m

ay be ways including this effect but

requiring further research.

2.2.3.R

eview of propeller coatings

The idea of coating a marine propeller is

not a new one. The first recorded idea w

as by H

olzapel (1904)

who

claimed

two

major

reasons for the coating of marine propellers,

as true today, namely to prevent fouling and

to reduce galvanic corrosion. Unfortunately

his comm

ents were not taken up at the tim

e and further investigation into the concept of coating m

arine propellers was not conducted

for some tim

e. It was not until the second

World

War

that further

development

of protective coatings for m

arine propellers was

conducted in order to conserve the scarce alloys usually used for propellers. C

ast steel is m

uch cheaper than bronze, can be easier to coat and requires less exacting m

anufacturing technology, so w

as proposed as an alternative. A

t least 4 ships had coated steel propellers installed during the w

ar. Three of them w

ere sunk

and unfortunately

no follow

-up w

as m

ade on the fourth Dashnaw

et al., (1980).

In demonstrating the effect of fouling on

propellers and its prevention by coating Kan

et al (1958) investigated the characteristics of

Tin-free SPC R

oughness profile:R

a = 3.26R

q = 4.04R

t = 19.98Sk = 0.01Ku = 3.29Sa = 2.57

-15

-10 -5 0 5 10 15 20

05

1015

2025

3035

4045

50

mm

micron

130

439


a fouled propeller using self-propulsion tests and full-scale trials w

ith the propeller covered in various rubber sheets to m

imic the fouling.

They found that small increases in roughness

will

cause large

increases in

delivered horsepow

er (DH

P), producing a worse effect

on propulsive efficiency than hull fouling but the reduction in thrust due to roughness w

as very sm

all. These experiments, how

ever, did not give very good agreem

ent with their full-

scale results.

The full-scale

measurem

ents show

ed that the rate of increase of DH

P will

decrease as the roughness increases; the initial roughness

has the

greatest effect

on perform

ance. Because of propeller fouling,

the DH

P decreases by 20% and from

these results, it can be seen that the effects of propeller fouling in term

s of a power penalty

are m

uch greater

than those

of surface

roughness.

Further work w

as conducted from the 50’s

to the 80’s particularly focusing upon the prevention

of cavitation

damage

e.g. by

Heathcock et al. (1979), A

ngell et al (1979) and

Akhtar

(1982). These

mostly

used ceram

ic coatings and were not just interested

in propellers but also, rudders, A-brackets and

turbine blades.

Dashnaw

et al. (1980) published their w

ork studying a large number of coatings and

surface finishes, in order to investigate those that m

ight prevent cavitation damage and

corrosion w

hile still

providing a

smooth

surface to minim

ise the hydrodynamic drag.

Their theory being that, if a suitable covering system

could be found it might be possible to

replace the expensive materials propellers that

are usually made from

by cheaper steel. They conducted tests using a 24 inch rotating disc apparatus

and found

that certain

urethane coatings could produce less drag than bare steel discs even w

ith a higher value of the root-m

ean-squared roughness amplitude, R

q. They concluded that there w

as a 10% change

in drag approximating to a 1%

change in pow

er at

the propeller,

although no

explanation as to how they arrived at these

figures was presented. Three coatings w

ere proposed

for further

evaluation and

were

coated onto blades of a 6.5m bronze propeller.

The tw

o coatings

were

polyurethane form

ulations and

one w

as an

undisclosed form

ulation (know

n as

Y-1).

They w

ere inspected after 2 and 11 m

onths in service. It w

as found that the polyurethanes had quickly delam

inated from the propeller. Y

-1 had fared better. From

these trials they realised that for any propeller coating, the bond strength of the adhesive/prim

er w

as of

fundamental

importance. They recom

mended that for the

broad surface area of the blades, under low

hydrodynamic loading, the coating needed an

adhesion strength of at least 8.92 kN/m

(50 lb/in.) of w

idth. Near the edges of the blades,

where

the surface

was

under high

and dynam

ic hydrodynam

ic loading,

a m

uch higher strength w

ould be needed.

Foster (1989)

described trials

on 2

Canadian

naval vessels

that had

their propellers

coated w

ith a

3-layer vinyl

antifouling system that used a cuprous oxide

containing topcoat. This was at the tim

e the standard system

used on the hulls of the C

anadian naval fleet. The first vessel, CFAV

Endeavour, found that, after 2 years in service, the coated propeller (the ship had tw

in screws

and only was one coated) w

as fouling free and only had sm

all amounts of paint loss on

the leading edges of the blades. They also found that the shaft grounding current of the coated propeller w

as reduced to about a third of

the uncoated

one (the

information

on current dem

and was taken from

the monthly

cathodic protection reports of both ships). The second

ship, the

naval frigate

HM

CS

MacK

enzie had both of her propellers coated. They w

ere examined by divers after 6 m

onths and

again in

dry-dock after

2.5 years

in service. The divers found that the coating w

as fouling free and alm

ost intact except for some

detachment along the leading edges and som

e sm

all isolated spots on the back of the blades. They also noted that the coating w

as still red in

color suggesting

that little

copper had

leached out. Once in dry-dock, it w

as found

440

Specialist Comm


that while still free from

fouling, the damage

had grown. The sm

all isolated spots on the back of the blade, m

ost likely caused by cavitation, had grow

n to a diameter of 5-

30mm

. A 30m

m w

ide strip had been eroded along the trailing edge and the top-coat had been rem

oved from the leading edge back to

about the mid-chord. The cathodic protection

reports showed that the current dem

and had dropped by about 30%

while at rest and at sea

by about 20% com

pared to the pre-coated condition.

They m

aintained these

figures throughout the 2.5 years in service.

Coldron and C

ondé (1990) reported on the Shell Engineer, a 1300dw

t coastal tanker, generating 905kw

at 250rpm through a 4

bladed nickel-alum

inum-bronze

propeller, 2.44m

in diameter. In 1983 it w

as selected to trial the effect of a TB

T-SPC based coating

on its propeller. This system w

as suggested by

the w

ealth of

published data

on the

coatings perform

ance on

ships hulls.

The propeller w

as removed, faired, w

et blasted and then dried before the coating system

was

applied. Two alternate blades w

ere coated w

ith a vinyl shop primer and 2 w

ith a 2 layer epoxy prim

er. The whole propeller w

as then coated

with

two

layers of

the TB

T-SPC

system (an extra coating w

as also added to the outer half of the blades. The roughness of the propeller before and after coating can be seen in Table 2. Table 2. A

comparison in the roughness of the

surface both before and after painting

Coldron and C

onde (1990)

R

a (2.5) R

tm (2.5)

Prior to

Painting23.2�m

110.3�m

A

fter Painting 14.2�m

43.7�m

%

Change

38.79%

60.38%

The propeller was inspected after both 6

and 12 weeks and w

as found that the TBT-

SPC coatings had rapidly been rem

oved from

the vinyl primer. The SPC

on the epoxy perform

ed better with only som

e mechanical

damage to the tip. The polishing rate of the

SPC

was

found to

be very

low

when

compared to that expected of a ship’s hull.

The epoxy was slow

ly ‘stripped’ back along the suction side from

the tip inwards so that

25% had been rem

oved after only 3 months.

In 1989, after 6 years in service, 20% of the

epoxy, near the blade roots, still remained on

the propeller

Further trials were conducted, this tim

e using a ceram

ic coating, in order to try and prevent a problem

with localized but random

cracking

of the

propellers of

the Shell

Marketer

class of

vessels C

oldron and

Condé (1990). Tw

o blades were, cleaned,

degreased, preheated

and the

grit blasted

before being coated not more than 40 m

ins after the surface preparation. The coating used w

as a ceramic m

ix, with an alum

ina base, w

ith 13% titanium

added (this improves the

impact resistance but reduces the electrical

resistance). The coating was applied using a

plasma

flame

spray system

w

ith argon/hydrogen

plasma

gas. The

two

remaining

blades w

ere prepared

to the

manufacturer’s standard finish. A

fter a period of 4 years, the propeller w

as inspected to find that the coated blades had actually becom

e sm

oother compared to their initial roughness

after coating. The uncoated blades, however,

had deteriorated

to a

surface about

50%

rougher than their initial value. The coating had m

anaged to remain attached, even in an

area where m

echanical damage had rem

oved part of the coating, there w

as no evidence of ‘creep

back’. A

lthough it

should be

considered highly

unreliable, due

to the

complex nature of the effect of propeller

condition on ship performance, it w

as also noted

that the

Shell M

arketeer w

as perform

ing 6% (in term

s of nautical miles per

tonnes of fuel) better than its sister-ship, the Shell Seafarer, w

hose blades had not been

131

441


coated, but were of a sim

ilar roughness to the Shell M

arketeer’s blades prior to their coating.

Matsushita

et al.

(1993) noted

that because the training ship of the Y

uge National

College of M

aritime Technology in Japan, the

Yuge-Maru, w

as at anchor for long periods, the propeller had a serious problem

with

biofouling. The seawater around its hom

e port ranged from

8-9°C to 27-28°C

, a wide variety

of adhesive

sea life

were

present in

the surrounding

waters,

including at

many

different species

of barnacle

(such as

Tintinnabulum rosa, Am

phitrite tesselatus and Am

phitrite haw

aiiensis), B

ryozoans (calcarious

colonial anim

als, sim

ilar to

corals), Serpulids

(a type

of tubew

orm),

mussels, oysters, algae and bacterial biofilm

. Therefore researchers at the college, as part of a w

ider investigation into the effect of a non toxic coating of silicone resin decided to coat the ship’s propeller. The coating system

had been developed as an industrial, non-polluting paint in such areas as seaw

ater suction pipes and cooling pipes of nuclear plants. Since there w

as no toxin present in the coating chem

istry it

was

considered safe

to the

environment.

The surface

had sim

ilar properties

to the

modern

Foul R

elease properties, w

ith a low surface energy and high

water repellence. The antifouling ability w

as derived from

the low attachm

ent strength of m

arine fouling organisms to the surface. This

was then the first reported experim

ent with a

FR

coating on

a m

arine propeller.

The propeller w

as first cleaned and then allowed

to foul

over a

six m

onth period.

Upon

inspection after this period it was found that

the propeller was heavily coated in fouling

(mostly bryozoans and serpulids) particularly

in areas of slow flow

speed over the surface e.g.

the boss

and blade

roots. A

fter the

inspection the propeller was then re-cleaned

and coated with silicone resin paint. 6 m

onths after

coating, the

propeller w

as again

inspected. The coating was found to be intact

and free from fouling except for a few

flat bryozoans

on the

root. A

fter a

further 6

months the propeller w

as inspected a third tim

e, again no damage to the coating w

as found, there w

as however, som

e bryozoans and slim

e fouling present. These results were

the first to show that a foul release coating

can remain attached to a propeller and achieve

effective antifouling in actual service.

In addition to the propeller inspections described above the fuel consum

ption was

recorded for both the un-coated and coated propellers w

ere recorded over the course of three

months

during the

summ

er fouling

breeding season. It was found that the fuel

consumption w

ith the 6.2% low

er when the

propeller was coated although the lack of

details about the change in hull condition over the trial period m

ean that this change cannot be attributed to the condition of the propeller alone.

The Yuge-Maru also had a large num

ber of sacrificial zinc anodes attached around the hull to protect the hull from

electrochemical

corrosion by

galvanic action

in seaw

ater, caused by the copper alloy propeller. Each side of the ship has 23 anodes attached to the shell plating, one in the bow

thruster tunnel, one on each of the upper and low

er bearings of the rudder post and one at the end of the stern tube, see Figure 2.

442

Specialist Comm


Figure 2 - A

rrangement of Sacrificial A

nodes (Zn Plates) on ship body of Yuge-Maru

(Matsushita

et al., 1993).

Table 3 shows the am

ount of degradation of the anodes of the course of a year w

ithout the

propeller being

coating and

as a

comparison the levels of degradation of the

replacement anodes over a year once the

propeller w

as coated.

The level

of deterioration w

as low for both cases (less than

5%); suggesting that the num

ber of anodes attached to the ship w

as excessive. The results did show

however, as expected, the anodes

near the propeller were the m

ost reduced (except num

ber 3, inside the bow thruster

tunnel). The

difference betw

een anode

degradation in

the uncoated

and coated

propeller condition was approxim

ately 30% in

favour of the coated propeller condition. This suggests that the propeller coating stopped or significantly reduced the galvanic current. In fact this has since been confirm

ed by more

recent research by Anderson et al. (2003)

who

conducted further

testing of

new

generation FR system

, on the propellers (and replacem

ent metal discs) of a 100

th detailed scale m

odel of a frigate, to investigate the effect of a propeller coating upon the current output

of an

Impressed

Current

Cathodic

Protection (ICC

P) system. They found that

the use of the coating “markedly reduced” the

ICC

P current output. When the coating w

as dam

aged, there was an increase in the output,

but this was still m

uch lower than the current

output of the uncoated disc. Although done on

a small scale, this is further strong evidence

that the

coating w

ill reduce

the galvanic

current caused by the propeller.

Within

the fram

ework

of galvanic

corrosion Atlar (2004) noted that som

e ship ow

ners and

propeller m

anufacturers m

ay think that partially coated propellers, w

hich can represent possible dam

age to paint or a paint failure, could be subjected to com

plex corrosion effect due to inherent differences in tw

o surfaces.

Although

such corrosive

damage has not been reported in any of the

vessels w

ith coated

propellers, w

ithin the

capability of

modern

cathodic protection

systems this should not be a problem

. His

consultation w

ith a

major

UK

propeller

manufacturer revealed that the final surface

finish of a large propeller by hand may take

about a month of tim

e while w

ith a machine

this will take at least a half of this period. In

the mean tim

e, the application of coating on propeller

surface w

ould require

relatively rough

surface, w

hich is

obtained by

grid blasting,

to provide

the coatings

with

a necessary grip to stick on the surface. B

ased upon

this requirem

ent, the

propeller m

anufacturer does not perform the final finish,

and hence save labour cost and delivery time,

132

443


while the paint m

anufacturer will apply grid

blasting directly on this surface. This way all

three parties:

the ow

ner; propeller

manufacturer

and paint

manufacturer

can benefit as w

ell as the environment

Table 3. Consum

ption of Sacrificial Anodes

(Zn plates) of the TS Yuge-M

aru. (M

atsushita et al., 1993)

Non-Propeller C

oatingPropeller C

oating(07.03.1989-28.02.1990)

(10.03.1990-04.03.1992)Zinc Anode

New

ZincR

ate of ZincZinc Anode

New

ZincR

ate of ZincPosition

Weight

Consum

ptionPosition

Weight

Consum

ptionN

umbe r

(Kg)(%

)N

umber

(Kg)

(%)

13.5

2.11

3.53.1

23.5

2.12

3.53.6

33.5

14.23

3.514.9

43.5

3.54

3.53.0

53.5

2.45

3.53.4

63.5

2.76

3.54.3

73.5

3.07

3.53.6

83.5

3.18

3.53.9

93.5

3.49

3.52.7

103.5

2.510

3.53.1

113.5

2.711

3.52.5

123.5

2.312

3.51.9

133.5

1.413

3.52.2

143.5

1.214

3.52.6

153.5

1.515

3.53.1

163.5

3.116

3.54.3

173.5

4.617

3.53.9

183.5

2.918

3.52.9

193.5

8.919

3.50.4

203.5

9.120

3.53.1

213.5

2.521

3.52.1

223.5

6.122

3.53.0

233.5

9.623

3.54.7

243.5

13.624

3.54.9

Subtotal84.0

4.5Subtotal

84.03.65

A5.2

12.6A

5.24.5

B2.2

2.2B

2.28.4

C4.0

4.0C

4.06.2

Total95.4

5.5Total

95.43.95

1-24=

Shell Plate (B-4)A

=U

pper Gudgeon

B=

Lower G

udgeonC

=End of Stern Tube

Another Japanese trial w

as conducted, this tim

e using the training ship Kakuyo M

aru A

raki et al., (2000) and Araki et al. (2001).

The ship’s

2.85m

diameter

propeller w

as coated w

ith a silicone resin (Bioclean D

X –

Chugoku M

arine Paint Com

pany Ltd.). After

1 year in service, the propeller was inspected

to find only light slime on the blades, w

ith only a little paint having been rem

oved from

the tips of the blades. Improvem

ents were

also noted in the rate of fuel oil consumption,

fuel oil pump index, and shaft horse pow

er required, com

pared to the fouled propeller,

although it was unlikely that this w

as due to the condition of the propeller alone.

Over the years propeller coatings have

been tested

that have

a w

ide range

of properties that effect propeller perform

ance and durability of coating. In the search for the perfect

propeller coating

a num

ber of

attributes have been highlighted as desirable. C

oldron and

Condé

(1990) defined

the attributes of an ideal propeller coating as follow

s:-

Exhibit adequate

erosion, abrasion,

corrosion and cavitation resistance and be resistant to im

pact damage and

penetration.

Posses anti-fouling characteristics or be

smooth

to sim

plify rem

oval of

marine biofouling.

R

etain an

acceptable level

of properties w

hen exposed to seawater

with low

water perm

eability to prevent degradation

of bond

strength by

corrosion of

the coating/substrate

interface.

Possess adequate

bond strength

initially and after prolonged seawater

imm

ersion to withstand the operating

conditions, including

maintenance

procedures.

Be non-conducting to reduce cathodic

protection current

requirements

by lim

iting the cathodic area.

The materials should be cheap, readily

available, and relatively easy to apply and repair.

The

coating m

ust be

capable of

inspection for

quality assurance

purposes.

The coating must be sufficiently thin

that it can be applied within the blade

thickness tolerance

range and

not require

expensive re-design

of the

propeller. In practice this implies a

coating in the thickness range of 100 to 250μm

.

To the above list it can be added two

further attributes,

that have

become

more

444

Specialist Comm


desirable in

the years

since C

oldron and

Condé published their list:

The coating

must

be as

environmentally benign as possible.

Preferred

to reduce

any radiated

signatures em

anating from

the

propeller as

much

as possible

(especially important for naval vessels

and cruise ships).

A num

ber of possible propeller coating types have been developed that each have som

e of the above attributes but not all of them

. The

possible types

were

listed by

Coldron

and C

ondé (1990)

as in

the follow

ing O

rganic Coatings

This is a wide ranging group of coating

types that

includes both

current SPC

technology

and Foul

Release

antifouling coating

technologies, epoxies,

vinyls, neoprenes, urethanes and polyam

ides (nylons). There are a w

ide range of possible application m

ethods such as airless spray, brush and roller. Som

e can even be coated onto the propeller in either a fluid or pow

dered state and then autoclaved to give the final coating, although such m

ethods are hard to use for large m

odern merchant propellers, due to the

need for an autoclave of sufficient size. M

etallic Coatings

A w

ide variety of metallic coating could

be considered for marine propellers. Som

e m

ay even have antifouling properties, if they contain

compounds

metals

with

known

antifouling properties such as Copper, Zinc,

Tin or other heavy metals. They could, in

theory, be deposited a number of different

methods, such as by electroplating, therm

al spray, w

eld overlay or vapour deposition. This group could also include, laser surface m

elting, when a thin layer of the surface is

heating to improve the surfaces resistance to

cavitation, e.g. Tang et al., (2004, 2005). The

development of these coating w

ould require large

scale facilities

to allow

m

erchant

propeller, typically of 5-10m diam

eter to be treated econom

ically. Metallic coatings also

suffer from the problem

of, if two dissim

ilar m

etals are in contact, a galvanic cell will form

causing accelerated corrosion. This is w

hy little research has been done on this type of coating for use on propellers. C

eramic C

oatings

This type

of coating

are created

a pow

dered m

ix of

mineral

substances including clays and m

etal oxides (aluminum

, chrom

e and titanium oxides are w

idely used) that are then fired (or specialist techniques, such as therm

al spray processes can be used) to produce a dense, low

porosity coatings. The properties vary w

idely, depending on w

hat chemicals are w

hat proportions of each chem

ical are used. They can be insulating or sem

i-conducting and

the hardness

can be

varied. They are

usually inert in seawater but not all can

withstand high levels of cavitation. Expensive

research into

the ideal

chemical

formula

would

be needed

before their

use as

a propeller coating w

ill become w

idespread.

No coating has yet been found to have all

the attributes in the list, so the perfect coating is still elusive. The current leading contenders for

a suitable

propeller coating

and their

properties com

pared to

the above

requirements can be seen (not in any order of

importance) in Table 4.

Table 4.The four systems currently m

ost likely to be developed as a propeller coating are

the tw

o leading

types of

antifouling system

(silicone based foul release and copper based SPC

) and metallic and ceram

ic type coatings. The qualities of each coating system

com

pared to the desired attributes are shown.

Those coloured green indicate that the system

exhibits that

attribute successfully,

orange indicates that the system

may exhibit that

attribute or

no evidence

for the

system

displaying that attribute was available and red

indicates that the attribute is not exhibited.

133

445


Silicone

Foul R

eleaseC

opper SPC

Metallic C

oating C

eramic C

oating

Resilience

to D

amage

Softer coating H

ard coating H

ard coating H

ard coating

Antifouling A

bility Proven

antifouling ability

Proven antifouling

ability U

nproven, possible

with som

e metals

Unproven,

No

mechanism

known

Inert in Seawater

Inert in seawater

Leaches away w

ith tim

e D

epends upon

the chem

istry used Inert in seaw

ater

Strong Attachm

ent Proven

attachment

to propellers Proven

attachment

to propellers U

nknown

attachment ability

Proven attachm

ent to propellers

Non C

onducting N

on conductor U

nknown,

may

conduct Likely

to be

conductor D

epends upon

ceramic used

Cheap

to develop

and produce A

lready in

production A

lready in

production D

evelopment

and m

aterial costs

required

Developm

ent and

material

costs required

Inspection of

Coating

Coating

easy to

inspect C

oating easy

to inspect

Depends on coating

used D

epends on coating used

Thickness

of C

oating~350m

ic, 3

layer system

C

oating thins

over tim

e Thin coating likely

Thin coating likely

Noise R

eduction Pliable, m

ay reduce N

oise N

o effect likely N

o effect likely N

o effect likely

Harm

ful to

environment

Non toxic

Toxic leachate D

epends upon

coating used N

on toxic

From the table it can be seen that silicone

based fouling release systems displays m

ore

of the attributes when com

pared to the other types of coating as w

ill be discussed further in the next.

2.2.4.R

eview of foul release coating technology

Foul Release (FR

) coating technology is the fore runner of the m

odern coating systems

for ship

propellers. In

comparison

to traditional

antifouling technologies,

FR

technology relies on a fundamentally different

concept of

fouling prevention.

Instead of

using the slow release of a biocide into the

surrounding w

ater, FR

coatings

work

by providing a surface to w

hich fouling species find it difficult to attach securely, this is know

n to

be “low

free

surface energy”

surface. The fouling is then removed from

the surface by hydrodynam

ic shear force.

The free energy of a surface, which is

comm

only referred to as “surface energy” or “surface tension”, is the excess energy of the m

olecules on the surface compared w

ith the m

olecules in

the therm

odynamically

homogenous interior. The size of the surface

energy represents the capability of the surface to interact spontaneously w

ith other materials,

Brady (1997). The surface energy and the

critical surface

tension of

surface are

determined by com

prehensive contact angle

analysis, using a variety of diagnostic liquids, m

easuring the angles that the liquid droplets m

ake with the coated surface. It is the surface

tension of a polymer w

hich is the property that has m

ost comm

only been correlated with

resistance to befouling, Brady and Singer

(2000).A

generalised relationship between

Surface Tension and the Relative am

ount of bio

Adhesion

has been

established and

presented in a graph comm

only known as the

“Baier curve”, w

hich does not display the m

inimum

relative

bio adhesion

(22~24 m

N/m

) at the lowest surface energy. A

variety of explanations has been given to account for this including the effects of elastic m

odulus (E),

thickness and

surface chem

istry of

coatings as discussed by Anderson

et al

(2002).Elastic m

odulus is key factor in bio adhesion and hence ability of organism

s to “release” from

a coating, Brady and Singer

(2000)and

Berling

et al

(2003). The

calculated Critical Free Surface Energy (�

c ) for a range of different polym

ers indicated that there w

as a better correlation between the

relative bio adhesion and (�c E) 1/2 than w

ith either

surface energy

or elastic

modulus,

446

Specialist Comm


Brady

and Singer

(2000). Thickness

is another characteristic of low

surface energy coatings that plays an im

portant role in bio adhesion.

It has

been found

that below

~100μm

dry film thickness barnacles can “cut

through” to the underlying coats and thus establish firm

adhesion. Above this thickness

there is no marked increase in FR

properties. The m

ajority of current FR coatings are based

on the

molecule

Polydimethylsiloxane

(PDM

S) which are generally form

ed by a condensation

mechanism

. This

long chain

polymer has a long flexible ‘backbone’ that,

along w

ith the

low

intermolecular

forces betw

een the methyl groups, allow

s it to adopt the

lowest

surface energy

configuration. PD

MS has, in air, a surface energy of 23-35

mN

/m and such low

er value of surface energy and its elastic nature m

akes PDM

S perfectly suited for use as a FR

type coating, Brady

and Singer (2000). In fact, for PDM

S and other silicone m

aterial,EC

�, w

as found to be at least an order of m

agnitude lower than

that of other materials (Singer et al., 2000). It

has been found that incorporation oils can enhance the FR

properties of PDM

S polymers,

Milne

(1977). O

ils, by

their nature,

are lubricants and therefore should decrease the friction, but this is not the m

ain reason for the efficacy of PD

MS. This is thought to be due

to the surface tension and hydrophobicity changes that the oils effect during the curing process and after im

mersion, T

ruby et al (2003).

When

Foul R

elease coatings

were

comm

ercially introduced in the mid-1990s

and applied to a high-speed catamaran ferry,

replacing a

toxic C

ontrolled D

epletion Polym

er (CD

P) antifouling, the recorded fuel consum

ption was low

er at the same service

speed, implying low

er drag characteristics as reported by M

illett and Anderson

(1997). As

a consequence a research project was set up at

New

castle University w

ith the objective of collecting data on the drag, boundary-layer and roughness characteristics of Foul R

elease and tin-free SPC

coatings, and to compare

them system

atically, Candries (2001) The

coatings used were a PD

MS Foul R

elease and a tin-free copper-pigm

ented acrylic SPC that

contained zinc pyrithione as a booster biocide.

Drag m

easurements w

ere carried out in tow

ing tank experiments w

ith two friction

planes of different size (2.5m and 6.3m

long), w

hich showed that the Foul R

elease system

exhibits less

drag than

the tin-free

SPC

system w

hen similarly applied. The difference

in frictional resistance varied between ca. 2

and 23%

, depending

on the

quality of

application as reported by Candries et al.

(2001).R

otor experiments w

ere also carried out

to m

easure the

difference in

torque betw

een uncoated

and variously

coated cylinders. In addition to coatings applied by spraying, a Foul R

elease surface applied by rollering w

as included because there were

indications that this type of application might

affect the

drag characteristics.

The m

easurements

indicated an

average 3.6%

difference

in local


coefficient between the sprayed Foul R

elease and

the sprayed

tin-free SPC

, but

the difference betw

een the rollered Foul Release

and the sprayed tin-free SPC w

as only2.2%

, C

andries et al. (2003)

The friction of a surface in fluid flow is

caused by the viscous effects and turbulence production in the boundary layer close to the surface.

A

study of

the boundary-layer

characteristics of the coatings was therefore

carried out in two different w

ater tunnels using

four-beam

two-com

ponent Laser

Doppler V

elocimetry (LD

V) and the coatings

were applied on 1m

long test sections that w

ere fitted in a 2.1m long flat plate set-up,

Candries and A

tlar (2005). Velocity profiles

were m

easured at five different streamw

ise locations and at five different free-stream

velocities. A

rollered surface and a sprayed Foul

Release

surface w

ere tested

to investigate the effect of application m

ethod. The m

easurements show

ed that the friction velocity

for Foul

Release

surfaces is

significantly low

er than

for tin-free

SPC

surfaces, w

hen sim

ilarly applied.

This

134

447


indicated that

at the

same

streamw

ise R

eynolds number the ratio of the inner layer

to the outer layer is smaller for Foul R

elease surfaces. The inner layer is that part of the boundary layer w

here major turbulence (and

hence drag)

production occurs.

Statistical analysis

of the

values of

the roughness

function obtained

by m

eans of

multiple

pairwise

comparison,

using Tukey’s

test, indicated that the roughness function for Foul R

elease surfaces is significantly lower than

for tin-free SPC surfaces at a 95%

confidence level. These findings are consistent w

ith the drag characteristics m

easured in the water

tunnel and rotor experiments

In addition to the difference in frictional resistance and the roughness function, the roughness

characteristics of

each of

the surfaces

were

investigated. The

average values

of their

roughness w

ere m

easured using the B

MT H

ull Roughness A

nalyser, w

hich is the stylus instrument in com

mon use

in dry-docks or underwater, for standardised

hull roughness measurem

ent. It measures R

t (50), w

hich is the highest peak to lowest

valley roughness

height over

a sam

pling length

of 50m

m.

Successive values

are averaged over a surface. It is clear from

the rotor experim

ents and the large plate towing

tank experiments that this single am

plitude param

eter does

not correlate

with

the m

easured drag

increase for

Foul R

elease surfaces, as it does w

ith SPC surfaces.

A detailed non-contact roughness analysis

was carried out w

ith an optical measurem

ent system

fitted

with

a 3m

W

laser. M

easurements w

ere taken on sample plates

coated alongside the surfaces tested in the tow

ing tank and water tunnel, and w

ere thus assum

ed representative of the test surface characteristics. In the case of the cylinders used in the rotor experim

ents, sections were

cut from the cylinders after testing, for use in

the optical measurem

ents. A m

oving average w

as applied

to filter

long-wavelength

curvature. The upper bandwidth lim

it or cut-off length w

as set at 2.5 and 5mm

, whereas

the low

er bandw

idth lim

it or

sampling

interval was set at 50m

m.

The detailed roughness analysis revealed that

when

long-wavelength

curvature has

been filtered out, the amplitude param

eters of the

sprayed Foul

Release

surfaces are

in general low

er than those of the rollered Foul R

elease surfaces

and the

SPC

surfaces. H

owever, the rollered Foul R

elease surfaces display a roughness height distribution w

hich is considerably m

ore leptokurtic (i.e. exhibits a larger num

ber of sharp roughness peaks) than the sprayed Foul R

elease surfaces. The greater num

ber of high peaks on the rollered Foul R

elease surfaces is expected to engender higher

drag than

sprayed Foul

Release

surfaces.

The main difference betw

een the Foul R

elease and the tin-free SPC system

s lies in the texture characteristics, as show

n in Figure 3 for tw

o typical roughness profilogram of

such coatings, applied by spraying. Whereas

the tin-free SPC surface displays a spiky

“closed” texture, the wavy “open” texture of

the Foul Release surface is characterised by a

smaller

proportion of

short-wavelength

roughness. This

is particularly

evident in

texture parameters such as the m

ean absolute slope and the fractal dim

ension. There is relatively little data available in the literature of irregularly rough surfaces on the influence of texture only on drag. G

rigson (1982) has m

entioned explicitly that open textures have a beneficial effect on drag.

It is clear that in order to correlate with

drag, the

roughness of

the generality

of irregularly rough surfaces needs to take both am

plitude and texture parameters into account,

e.g. Musker (1977) and T

ownsin and D

ey (1990). B

ased on the experiments presented,

it was thought that the rheology of the paint,

which

is significantly

different for

foul-release and tin-free SPC

coatings, had a direct effect

on its

texture, w

hereas am

plitudes depend significantly on the application quality. A

correlation

analysis of

the texture

448

Specialist Comm


parameters w

ith the amplitude param

eters, how

ever, has shown that the tw

o are inter-related,

so that

bad application

can be

expected to have a knock-on effect on the texture param

eters

At present, the procedure adopted by the

International Tow

ing Tank

Com

mittee

(ITTC) to correlate roughness w

ith drag only accounts for a single roughness am

plitude param

eter, IT

TC

(1990).

The procedure

hinges on the use of a practical formula for

the added

ship resistance

(or roughness

correlation allowance), w

hich was proposed

by Tow

nsin and Dey (1990) in term

s of A

verage Hull R

oughness for the moderately

rough ship range where R

t(50) is less than ��m

. Unfortunately, this procedure m

ay not w

ork for foul-release surfaces, unless a texture param

eter is included in the roughness

characterisation. For

a selection

of 41

different coated surfaces, including 8 newly

applied foul-release surfaces, Candries and

Atlar (2003) found that the m

easured drag correlated

reasonably w

ell best

when

the roughness m

easure, h, is characterised by h = 1/2R

a.�a where R

a is the average roughness am

plitude while��a is the m

ean absolute slope. There w

as a need for further testing and correlation studies to provide further support for this correlation.

Figure 3. Typical roughness profilogram

s taken from a tin free SPC

coated surface, Ecoloflex, (above) and Foul R

elease, Intrersleek 700, coated surface (below) using laser profilom

etry, C

andries and Atlar (2003)

135

449


2.2.5.Foul release coating research – as applied to propellers

While the earlier sum

marized research on

the FR coatings w

as continuing to understand their general drag reduction m

echanism, there

was further interest from

industry to research on the application of these coating system

s on propellers in the follow

ing two areas: (1) if

the FR coatings can successfully stay on yacht

propellers in arduous conditions; (2) if the FR

coatings can display any performance benefit

for a large comm

ercial vessel propeller that w

as coated with the earlier m

entioned FR

system, Intersleek 700 (IS700). In addressing

at the first investigation area (1), a pilot experim

ental study was conducted w

ith a 3-bladed,

300mm

diam

eter, alum

inum

alloy m

odel of a comm

ercial motorboat propeller.

The model w

as coated by IS700 using a rollering technique as opposed to spraying to sim

ulate a real life scenario for small craft

owners. O

pen water tests w

ere conducted in the Em

erson Cavitation Tunnel of N

ewcastle

University

in atm

ospheric and

reduced vacuum

condition.

In the

latter case

the propeller w

as exposed to several hours of cavitating condition to check on the adherence resilience

of the

FR

system.

In the

atmospheric condition a slight increase in

propeller efficiency of 0.16% w

as recorded. In a vacuum

condition (equivalent to the

scaled service condition of the propeller) a slight drop in efficiency (2.48%

) was noted.

Neither of these values w

as large enough to say that the coating m

ade a significant change to the propeller efficiency beyond that of experim

ental error. It was noted that w

ith the coating

the inception

of the

tip vortex

cavitation appeared at approximately a 5%

low

er value of the rpm for the uncoated

propeller, although this could easily be due to the poor application of the coating (applied by brush) or m

echanical damage on the leading

edges of the blades. No adverse effect of the

coating to the extent of the cavitation was

noted whilst the coating stayed intact until the

end of these tests except small peeling off at

the sharp edges, Candries et al. (1999). In

addressing at the second stage investigations (2) m

ore through and long term research w

as planned. This has involved num

erical and experim

ental investigations as well as full-

scale trials / observations to demonstrate if

there were any benefits or disadvantages of

applying FR coating on propellers in term

s of propeller

efficiency, effect

on cavitation

inception, type and extent of cavitation and underw

ater noise emission from

propellers. The follow

ing section gives a brief review

and findindgs from these investigations.

2.2.6.Effects on propeller efficiency

Based upon som

e plausible fuel saving reports after the application of IS700 coating on the propeller of a 100,000 D

WT tanker, it

was decided to use the propeller of this vessel

as the benchmark propeller for the N

ewcastle

University

propeller coating

research, and

some num

erical and experimental w

ork was

conducted w

ith the

scaled m

odel of

this propeller w

ith the following m

ain particulars given in Table 5 and operating conditions given in Table 6.

Table 5. Main particulars of the basis vessel and propeller

Propeller V

essel D

iameter, D

6.85 m

Ship type

Medium

sized tanker

Pitch Ratio, P/D

0.699

Deadw

eight 96920 tonnes

Expanded Blade A

rea Ratio,

AE /A

0

0.524 Length O

verall, L

OA

243.28 m

450

Specialist Comm


Num

ber of Blades, Z

4 M

ax Draught, T

13.62 m

Design A

dvance Coefficient, JA

0.48 Speed

14.86 knots

Direction of rotation

Right/H

Pow

er(installed) 9893 kW

Scale ratio, �

19.57 Y

ear built 1992

Table 6. Operational conditions

Fully L

oaded C

onditionB

allast Condition

Cavitation num

ber, �0.520

0.334

Propeller imm

ersion, H (m

) 10

4.66

Propeller speed (RPM

) 100

104

Design J

A0.48

0.486 J range tested

0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, 0.40

Atlar et al (2002) conducted num

erical investigations on the open w

ater performance

analysis of this propeller by using a boundary elem

ent theory based lifting surface analysis tool in w

hich the effect of the FR coating w

as sim

ulated in the appropriately selected drag coefficients of the propeller blade section. In this selection the increase in section frictional drag due to roughness w

as represented by the expression given by M

osaad (1986) as:

��

��

�

��

3/1

093.0

Re

5.4

'3 1

Re

1.8

1000c

hC

F

Where

Re

is the

blade section

Reynolds’ N

umber; c is the section chord

length; h’

is the

roughness param

eter as

defined by Musker described earlier. V

alues for h’ for the various R

ubert surfaces were

calculated by Mosaad

and are given in Table 7.

Table 7. Musker’s characteristic roughness

measure of R

ubert gauge surfaces. Rubert Surface

h' (�m

)

A1.32

B3.4

C14.8

D49.2

E160

F252

The total drag coefficient was represented

by the sum of the frictional drag and the form

drag as in the follow

ing where t is being the

thickness of the blade section: F

DC

ct

C�

�

�)

/1(

2

In consultation with a m

ajor UK

propeller m

anufacturer, it

was

assumed

that a

roughness equivalent to Rubert A

represented a

degree of

smoothness

unlikely to

be achieved in practice. R

ubert B w

as considered characteristic

of a

new

or w

ell polished

propeller and

Rubert

D

to E

would

be equivalent to the blade roughness after 1 to 2 years in service. In the num

erical analysis it w

as assum

ed that

the new

or

polished propeller had R

ubert B blade surfaces, the

drag of which w

as represented by the design C

D values taken from B

urrill (1955-56). The increase in C

D caused by blade roughening w

as then given by the difference between the

�C

D values

corresponding to

the R

ubert surface in question and that for R

ubert B. The

effect of the increased roughness on the drag coefficient for the section at r/R

= 0.7 is show

n in Table 8.

136

451


Table 8. Drag coefficients of R

ubert surfaces (D

esign = Rubert B

). Surface

Design

Rubert D

RubertE

RubertF

CD

0.008338

0.01003

0.01138

0.01206

%Increase

19.7 35.8

43.9

The key decision on this analysis was the

determination

of characteristic

roughness values (h’) for the foul release coated blade surfaces. In this decision the m

easurements

made

with

the FR

coated

flat plates

by C

andries (2001) played an important role.

The surface

characteristics of

5 different

applications w

ere studied

using a

UB

M

Optical M

easurement System

from w

hich it w

as found that the roughness measure h’

varied between 0.5 and 5�m

. The quality of application ranged from

excellent to good, so that it w

as considered appropriate to assume a

value of h’ = 5�m. The calculated values

were

negligibly different

from

those calculated w

hen using the Design C

D values. From

this it can be inferred that a foul release coated blade surface w

as equivalent to the new

or well polished blade surface.

Based

on the

above assum

ption the

sectional drag coefficients in the numerical

tool w

as m

odified and

the propeller

performance w

ith the design CD values w

as first

was

calculated for

varying operating

(advance coefficient)

conditions and

this procedure w

as then repeated with the drag

coefficients corresponding to Rubert D

, E and F

surfaces for

the sam

e conditions.

The results of the com

parisons were presented in

the open water curves of this propeller as

shown in Figure 4 w

here the predominant

effect of an increase in the roughness of the propeller

blades w

as an

increase in

the propeller torque. The decrease in propeller thrust that accom

panies the increased torque w

as too small to be obvious on the figure’s

scale.

Figure 4. Propeller open w

ater characteristics for various values of blade surface roughness, A

tlar et al (2002).

The loss in propeller efficiency (�� as the

propeller blades

roughen, to

a base

J, is

shown by Figure 5. Perform

ance data for the subject vessel from

which the propeller w

as m

odelled showed that on average propeller

worked at a value of J = 0.48. A

s shown in

Figure 3 the propeller efficiency losses due to blade

roughening (or

gains by

keeping propeller

clean) w

ere about

3%,

5%

and 6%

for surfaces of roughness represented by R

ubert D, E and F, respectively. In sum

mary,

this num

erical investigation

showed

that significant

losses in

propulsive efficiency

resulting from

blade

roughening can

be regained by cleaning and polishing of the blades.

Alternatively,

the efficiency

losses could be avoided, perhaps indefinitely, by the application of a paint system

that gives a surface finish equivalent to that of a new

or w

ell-polished propeller.

A

foul release

coating could be such a paint system.

Atlar et al (2003) conducted the sim

ilar analysis, this tim

e applied on high-speed and large surface area propellers. The sim

ulations for the open w

ater performance of the G

awn-

Burrill Series based propeller of a tw

in-screw

patrol gun

boat indicated

rather plausible

efficiency gain (or loss) which w

as almost

twice the m

aximum

efficiency gain (or loss)

452

Specialist Comm


obtained w

ith the

earlier reported

tanker propeller. This w

as related to the high speed and larger blade surface area of the propeller. W

hile the

above described

numerical

investigations revealed attractive potential of the

FR

coating for

efficiency gain,

experimental investigations w

ere conducted

to confirm on this potential w

ith a scaled m

odel of the earlier described basis tanker propeller in the Em

erson Cavitation Tunnel.

The model w

as constructed from alum

inium

to a scale of 1:19.57 so that multiple sets of

blades, manufactured w

ith great accuracy can be installed or replaced easily.

Figure 5. Loss in efficiency in going from

Design D

rag Coefficient to specified R

ubert Surfaces, A

tlar et al (2002).

This allowed rapid and reversible changes

between the coated and uncoated condition.

One set of blades w

as coated with the IS700

FR system

which w

as a three layer system

consisting of an epoxy basecoat, a silicon

polymer top coat and a tie coat betw

een these tw

o for good bonding. The whole system

dried to a film

thickness of between 320 and

360mic. The uncoated and coated propeller

model can be seen in Figure 6.

Figure 6. M

odel Propeller with uncoated (left) and coated (right) blades, M

utton et al (2005)

Results from

the tests were discussed by

Mutton et al (2005) and Figure 7 show

s the findings from

the open water tests. A

s shown

in this

figure there

was

little difference

between the coated and uncoated condition

for the favour of the coated condition at higher values of advance coefficients. The

slight change was due to the slight decrease in

the m

easured torque

as observed

in the

numerical sim

ulations. The open water tests

were repeated at a reduced vacuum

, which

corresponded to the fully-loaded condition of the vessel. This did not show

any change in the

efficiency at

the design

operating condition.

137

453


C

om

paris

on

of O

pen

Wate

r Ch

ara

cte

ristic

s in

Atm

osp

heric

co

nd

ition

(wate

r sp

eed

4m

s-1

, Co

nfid

en

ce lim

its 9

5%

)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.80

.25

0.3

50.4

50.5

50

.65

0.7

50

.85

Ad

van

ce

Co

effic

ien

t, J

Kt, 10Kq, Efficiency

unco

ate

d K

tu

nco

ate

d 1

0K

qu

nco

ate

d E

fficie

ncy

co

ate

d K

tco

ate

d 1

0K

qco

ate

d E

fficie

ncy

Figure 7. O

pen water curves for the uncoated and coated propeller. A

slight reduction in torque at higher advance coefficient has led to an increase in efficiency for the coated propeller. The design operating condition for this propeller is J=0.48; no difference is detected in perform

ance at this condition, Mutton et al

(2005).

Examination

of full-scale

propellers coated w

ith FR system

s has demonstrated that,

like all propeller coatings, the Foul Release

coating is prone to suffering damage from

to cavitation and hitting objects in the w

ater. This is usually about 5-10%

of the coating surface area and predom

inantly on the blades leading edge, trailing edge and tip regions. It w

as suggested

that this

damage

may

significantly affect the performance of the

propeller as

well

as prom

oting early

cavitation inception

and encourage

further cavitation developm

ent in the damaged areas.

To investigate these effects Mutton et al

(2005) imparted different levels of typical

damages onto this m

odel propeller’s coating to investigate the dam

age effects. These tests indicated that the dam

age to the coating had to be extensive before significant reduction in efficiency to occur.

One of the im

portant aspects affecting the foul releasing ability of these coatings is the low

er threshold

of a

vessel’s continuous

operational speed.

Early generation

FR

coatings had relatively high threshold (e.g. 18 knots and beyond) to be effective w

hilst this lim

it has been reducing (e.g. 12 knots and below

) w

ith recent

development

in this

coating technology.

In parallel

to this

development, in the early stages of the above

described research at New

castle University

the com

mercial

FR

system

used w

as International Paint’s Intersleek 700 (IS700). A

fter the

introduction of

the recent

comm

ercial product, Intersleek 900 (IS900), the above propeller perform

ance tests were

repeated w

ith this

latest coating

system

applied on

the sam

e m

odel propeller

by K

orkut and Atlar (2009). U

sing the latest application

technology it

was

possibly to

achieve a dry film thickness of 250�m

with

the three layer coating system as opposed to a

350�m thickness of the earlier tests. The open

water perform

ance tests revealed an average 1%

difference in the efficiency values over the entire J range for the favour of uncoated blades. B

oth thrust and torque values were

slightly increased by 1.9% and 0.9%

with the

effect of coating, respectively. In overall the difference

in the

average efficiency

was

within the uncertainty level of the open w

ater tests

which

was

3%,

similar

to the

conclusions by Mutton et al (2005) although

the trend in the previous tests was in favour of

coated blades.

How

ever in

their experim

ental study,

Korkut and A

tlar (2009) withdrew

attention

454

Specialist Comm


on the

applied paint

thickness such

that, ow

ing to

the practical

limitation

of the

application technique of the particular coating, w

hich w

as airless

spraying, the

coating thickness applied on the m

odel propeller was

almost sim

ilar to the coating thickness at full-scale. This w

ould require further investigation on scaled coating thickness and appropriate scaling law

.

Within the sam

e framew

ork another recent experim

ental investigation on the application of

new

FR

coating on

model

propeller perform

ance was reported by A

tlar et al (2010) as part of the recently com

pleted EC-

FP6 integrated R&

D project A

MB

IO w

hich aim

ed to

develop non-toxic

antifouling benefited from

nano technology engineering to prevent or reduce the grow

th of biofouling in the m

arine environment, A

MB

IO (2010).

In this project, one of many new

ly formulated

and tested FR coatings w

as TNO

-008 which

was

based on

nano-engineered Sol-gel

technology by TNO

. This coating was applied

on the earlier described benchmark m

odel propeller using spraying technique and cured by heating up to 125 deg. The nature of the coating

and the

application technology

enabled to apply this coating at a desired thickness such that it w

as possible to achieve an average roughness w

hich was 54%

less than

the roughness

achieved w

ith the

Intersleek 900 (IS900). The comparisons of

the open

water

test results

of the

model

propeller w

ith the

IS900 and

TNO

-E008 coatings show

ed similar torque characteristics,

with little difference observed betw

een the 2 coatings.

How

ever the

TNO

-E008 coating

gave a higher thrust value for the same rpm

w

hen compared to the IS900 coating such that

the efficiency increase could be as high as 4%

when com

pared to the IS900 at the maxim

um

efficiency. Whilst this finding appears to be

too plausible requiring further investigations at

least by

applying on

other types

of propellers and to test, the m

ost interesting nature of this new

coating technology was the

flexibility in the application thickness that can be adjusted to m

eet a scaling criterion that can be found betw

een the model and full-scale

paint thickness.

In order

to investigate

the effect

of propeller coating on ship’s perform

ance in full-scale and controlled m

anner, Mutton et

al (2003) conducted a series of comparative

dedicated full scale trials for the first time

with the FR

coated and uncoated propellers. This

was

over a

measured

mile

with

New

castle U

niversity’s Ex-R

/V

Bernicia

which w

as based on the design of a fishing vessel and m

ainly used for estuarine and coastal research. The m

ain particulars of the R

/V and its single screw

are given in Table 8 and 9, respectively.

�Table 9. The general particulars of R

V B

ernicia O

verall length 16.2 m

B

eeam

4.72m

Draft

2.59m

Gross tonnage

46.25 tons Engine (M

CR

) 150H

P @ 1500rpm

G

ear box ratio 3.4:1

Maxim

um ship speed

9 knots Table 10. M

ain particulars of the R/V

Bernicia propeller

Diam

eter 1.14m

M

ean face pitch 0.9m

Expanded B

AR

0.466

Blade num

bere 4

Rotation

Right hand

Max rpm

440

138

455


The initial trials were conducted w

ith its clean but uncoated propeller before being placed on the slip and its propeller rem

oved to be coated by IS700 using spraying at the paint m

anufacturer’s site.

Another

series of

measured m

ile trials were then conducted for

the same loading conditions applied w

ith the uncoated

propeller trials.

Shaft torque,

shaft/vessel speeds

and all

other relevant

parameter m

easurements w

ere recorded for analysis and further corrections. The conduct of the trials and analyses w

ere carried out using

the B

SRA

standard

procedure and

details of these measurem

ents can be found in

Mutton et al (2003). A

s shown in Figure 8,

despite the weather affecting the coated trials,

the results showed little difference betw

een the shaft pow

er performance of the coated and

uncoated propellers.

Although

the sea

trials proved

inconclusive due

to poor

weather,

in m

easuring the

short term

increase

in perform

ance due to the application of the coating, in the first three years since the trials took place, the propeller w

as inspected at both 12, 24 and 36 m

onths’ The state of the propellers at these inspections are show

n at pictures in Figure 9, M

utton et al (2005).

Final Power Curve Com

parisonErrors estim

ated at 10%

0.00

20000.00

40000.00

60000.00

80000.00

100000.00

120000.00

140000.006.006.50

7.007.50

8.008.50

9.009.50

Tide Corrected Speed over Ground (knots )

Corrected Shaft Power (Watts)

Uncoated Trial

Coated Trial

Figure 8: The final R

esults of the Bernicia sea trials show

no statistical difference between the tw

o curves. The trials w

ere particularly affected by the weather leading to large error estim

ates and m

aking the results inconclusive, Mutton et al (2005).

As show

n in these pictures the coating w

as found to be in good condition, 95% intact,

except for slight removal of the coating at the

edges and tip of the blades. The results have show

n that despite the vessel operating in a heavy

fouling, coastal

and estuarine

environment, little fouling w

as returned to the

propeller. What fouling w

as returned is a light ‘slim

e’ layer that could be easily removed

with a dam

p cloth. This was very different for

the uncoated propeller where after 14 m

onths in

service after

a polish,

hard shelled

barnacles were present to about half the blade

radius that can only be removed by scrubbing..

456

Specialist Comm


12 m

onths 24 months 36 m

onths (back) Figure 9.: The coated propeller of B

ernicia after 12, 24 and 36 months in service, M

utton et al (2005)

Roughness m

easurements w

ere taken on the

Bernicia

propeller using

stylus type

roughness gauge (Surtronic 3+) before and after the coating applied as w

ell as after 1 year vessel w

as in service with the coated

propeller. As show

n in Figure 10 the average of the m

ean roughness amplitude (R

a, with a

cut-off length of 2.5mm

) and its distribution

was significantly different in favour of the

coated propeller. There was som

e measured

difference between the new

ly applied coating and the coating after 12 m

onths in service. This w

as mostly due to the presence of the

slime layer on the blades w

hich can easily be rem

oved and some slight m

echanical damage

to the coating.

Ra Frequency D

istribution for the Uncoated Propeller, the N

ewly C

oated Propeller and after 1yr in Service

0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

02

46

810

1214

1618

2022

2426

28R

a value (microns)

% Frequency

New

Coating

Coating After 1yr in Service

Uncoated Propeller

Figure 10. The m

ean roughness amplitude, R

a, frequency distributions measured on the propeller of

R/V

Bernicia before coating, after coating and after a period w

ith the coating in service. Figure 11 show

s the mean spacing distance

between profile peaks frequency distribution

(Sm) m

easured on the Bernicia’s propeller.

This is a measure of the surface texture w

here the larger the value, the m

ore ‘open’ the texture. The coated propeller exhibits a m

uch w

ider range

of m

ean spacing,

while

the uncoated propeller had a m

uch smaller range.

As show

n in Figure 11, after a year in service the frequency distribution of Sm

has changed

little and

still exhibited

the w

ider range.

Mutton

et al

(2005) concluded

that the

coating significantly changed the roughness characteristics of the propeller blade surface and

that the

roughness did

not change

significantly after 12 months in service. The

coating had

the effect

of preventing

the increases

in roughness

usually seen

with

uncoated propellers as well as keeping the

R/V

propeller remarkably free from

major

fouling m

ore than

3 years

which

was

impossible w

ith her uncoated propeller.

139

457


Sm Frequency D

istribution for the Uncoated propeller, N

ewly A

pplied C

oating and After 1yr in Service

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0500

10001500

20002500

30003500

4000

Sm Value (M

icrons)

% FrequencyN

ew C

oating1yr in S

erviceU

ncoated Propeller

Figure 11. The m

ean spacing between profile peaks, Sm

, frequency distribution. Measured on the

propeller of Bernicia before coating, after coating and after a period w

ith the coating in service. T

ask 2.3. The E

ffect of Coating on the C

avitation Behaviour

The effect of coating on the cavitation perform

ance of

a propeller

can be

as im

portant as on its efficiency or even more

for a quiet propeller. Nevertheless, there is

hardly any data reported on this subject in the open

literature except

some

anecdotal reporting

from

full-scale and

limited

experimental

investigations conducted

at N

ewcastle

University.

These investigations

have focused on the effect of different types FR

coatings on the cavitation inception, and type and extent of fully developed cavitation observed on the earlier m

entioned bench mark

tanker propeller

tests sum

marised

in the

following.

Cavitation

inception is

a com

plex phenom

enon w

hich is

far from

being

completely

understood at

present. The

mechanism

s underlying this phenomenon are

thought to be threefold: (1) water quality

(mainly nuclei content and its statistics); (2)

the growth of the boundary layer over the

blade sections; and (3) type of cavitation to be developed. A

mongst them

, it is most likely

that the growth of the boundary layer w

ill be m

ost affected by the presence of coating w

hile the type of cavitation may also be

affected.

In the case of a “surface” cavitation, as oppose to a “vortex” type, inception occurs in the region of the boundary layer transition. In this

respect, propeller

blade roughness

stimulates the transition of the boundary layer

from lam

inar to turbulent flow and hence

causes cavitation inception. The Foul Release

coatings are expected to delay such transition from

the laminar to the turbulent flow

and hence

the associated

delay in

cavitation inception w

ill also be expected. How

ever, this effect m

ay not be so important for full-scale

propellers which operate in fully turbulent

regime. Even if it is lim

ited to the leading edge regions, this effect can be im

portant for special propellers designed to avoid cavitation. A

nother interesting nature of the visco-elastic m

aterials, like the silicon coating, is their effect to alter the turbulence characteristics of the

flow

near the

wall

and even

“re-lam

inarise” the turbulent flow. This w

ill not only affect the cavitation inception but also influence the characteristics of the developed cavitation. In contrast, the protuberances of uncoated and not w

ell-maintained rough blade

surfaces are

expected to

destabilise the

vortices more quickly and creating bubble

residence locations,

and hence

reduce the

cavitation strength of the water.

458

Specialist Comm


In the case of “vortex” type cavitation, particularly in the tip vortex type, the nature of the vortex is strongly dependent upon the nature of the boundary layer over blade in the tip region, w

hich can be affected by the coating. If the boundary layer separates near the tip then the tip vortex w

ill be attached to the blade w

hile the preservation of a laminar

flow near the tip can avoid the detachm

ent of tip vortices.

The effect of FR coating on the cavitation

inception was first reported by M

utton et al (2006) on the tests conducted in the Em

erson C

avitation Tunnel with the earlier described

benchmark tanker propeller. The m

odel of this

propeller w

as tested

with

its blades

uncoated and

coated w

ith Intersleek

700 (IS700) in uniform

flow at reduced vacuum

levels

simulating

the loaded

and ballast

operating conditions of the tanker. Careful

recordings of the cavitation inception of a thin unattached tip vortex indicated slight delay in inception due to the FR

coating in the loaded condition

whilst

this trend

was

somehow

reversed in the ballast condition. In overall it w

as concluded that the effect of coating on cavitation inception w

as not significant. On

the other hand, the nature and extent of the developed

cavitation patterns,

which

were

mainly tip vortex and sheet cavitations, w

ere

somehow

different such that the uncoated propeller tip vortex w

as thicker while the

extent of sheet cavitation was relatively large

compared

to the

coated propeller

blade cavitations. H

owever, the uncoated propeller

cavitation pattern was m

ore stable compared

to the coated one. The unstable nature of the coated sheet cavitation som

etimes caused it to

break up

into m

isty and

cloud types

of cavitation along the low

er boundary of the cavity sheet. A

lthough it was not published

the effect of coating damage on cavitation

was also explored by various scenarios and no

evidence was found that the coating dam

age w

ould cause

further cavitation

on this

propeller model.

In a recent follow up investigation to the

above study,

Korkut

and A

tlar (2009)

conducted further experimental investigations

onto the effect of coatings on the cavitation inception and cavitation extent on the sam

e benchm

ark propeller

but using

latest com

mercial FR

product, IS900. Furthermore

they also explored the effect of non-uniform

flow by testing the m

odel propeller behind a w

ake screen.

The results

of the

inception/desinence test are shown in Table

11 where the cavitation inceptin num

ber is defined based on the resultant flow

velocity com

bined w

ith the

advance speed

and rotational speed at 0.7R

.

Table 11. Cavitation inception test results w

ith uncoated and coated blades in uniform and non-

uniform flow

cases, Korkut &

Atlar (2009)

U

niform

Non-U

niform

Cavitation T

ype U

ncoatedC

oatedU

ncoatedC

oated U

nattached tip vortex cavitation-inception

0.685 0.679

0.982 0.984

Unattached tip vortex

cavitation-desinence 0.683

0.677 0.980

0.983

Attached to all blades

0.606 0.611

0.701 0.695

140

459


As show

n in the table the coating of the blade did not change the cavitation inception characteristics

of the

model

propeller (difference is less than 1%

), if the coating applied correctly (i.e. avoiding sagging of paint at sharp blade edges that m

ay cause unrealistic cavitation pattaern and singing). K

orkut and Atlar related this to the sim

ilar roughness and surface texture characteristics of both uncoated and coated blades m

easured w

ith the model. H

owever this m

ay not be the case in full-scale applications, w

here some

advantage of smooth FR

surface finish can be expected,

by delaying

the inception

of cavitation.

As

far as

the cavitation

extent w

as concerned,

the uncoated

blades displayed

slightly more extended cavitation than those

of the coated blades from tip vortex to sheet

vortex type for both loading conditions as

shown

in Figure

12 for

the fully

loaded condition.

In a recent study by Sampson and A

tlar (2010) the cavitation inception and extent characteristics of the sam

e model propeller

were

compared

as uncoated,

coated w

ith IS900

and the

earlier described

AM

BIO

project

coating (TN

O-E008).

These tests

indicated some delay in cavitation inception

for IS900

compared

to the

uncoated and

TNO

-008 coated

blades. A

nalysis of

the cavitation patterns w

as subjective owing to

the resolution

of the

video cam

era. The

predominant

cavitation on

the blade

was

steady sheet

cavitation and

developed tip

vortex cavitation in the propeller slipstream

which had greater extent on the uncoated

blade and similar but slightly less presence on

the coated

blades w

ith non-discernable

difference between them

as shown in Figure

13.

J=0.50 Uniform

J=0.50 Non-U

niform

460

Specialist Comm

ittee on Surface Treatment J=0.40 U

niform

J=0.40 Non-U

niform

(a) (b)

Figure 12. C

avitation developments in uniform

and non-uniform flow

conditions at varying advance coefficients for fully loaded condition: (a) uncoated; (b) coated by IS900.

Korkut &

Atlar (2009)

Figure 13. Cavitation com

parison of the 3 blades (Uncoated, IP900, T

NO

-E008)

at J = 0.35 and atmospheric condition. A

tlar et al (2010)

Task 2.4. T

he effect of Coating on C

omfort (Propeller noise)

Similar

to the

lack of

research on

cavitation, virtually there is also no published data on the effect of FR

coating on propeller noise available in the open literature, apart from

the limited investigation conducted at

New

castle University by M

utton et al (2006) and K

orkut & A

tlar (2009).

There are four principal mechanism

s by w

hich a

propeller can

generate sound

pressures in water, C

arlton (2009). These are associated w

ith: (1) the displacement of the

water by the blade profiles; (2) im

migration

of flow from

the pressure to the suction side of

the blades

in developing

thrust; (3)

fluctuating volume of cavitation on the blades

when cavitation develops on the blades of

propeller operating

in non-uniform

w

ake flow

; and (4) collapse of cavitating bubble and/or bursting of a cavitating vortex.

Of

the above

four m

echanisms

of generating propeller noise the first tw

o are associated

with

“non-cavitating” propeller

flow w

hile the latter two w

ith the “cavitating”

141

461


flow. The non-cavitating com

ponent of sound pressures w

ill have distinct tones – known as

the blade rate noise- associated with discrete

(lower)

blade frequencies

together w

ith a

broad-band noise at higher frequencies. The blade rate noise is closely associated w

ith the unsteadiness

caused by

circumferentially

varying wake field in w

hich the propeller operates. This causes a fluctuation in the angle of attack of the propeller blade sections and hence sound pressure. H

owever this can

hardly be affected by the presence of the coating. O

n the other hand the broad-band noise

is m

ostly affected

by the

level of

turbulence in

the incident

flow

and its

interaction w

ith the

wall

boundary layer

which w

ill be affected by the coating. One of

the important m

echanisms contributing to the

broad-band noise is the trailing edge noise, w

hich is perhaps the least well understood

mechanism

. The role of the turbulence in the boundary layer is a crucial param

eter, which

will be affected by the presence of coating,

while this noise com

ponent would suffer from

the effect of possible fouling w

ith uncoated propeller as w

ell as from hydro-elastic effects

of the

coated blades.

The collapse

of cavitation bubbles creates shock w

aves and hence cavitation noise. This is m

anifested as m

ostly ‘white noise’ in a frequency band up

to around 1MH

z. It is thought that the coating w

ill mostly affect the trailing edge noise and

may even act as a dam

per by absorbing the energy of cavitation noise due to its flexible nature.

The investigation

of the

effect of

FR

coating on propeller noise was also part of the

experimental

work

on the

efficiency and

cavitation investigations with the benchm

ark propeller

reviewed

earlier. The

noise investigations

therefore conducted

at tw

o experim

ental cam

paigns: in

the first,

the benchm

ark m

odel propeller

uncoated and

coated with IS700 tested in uniform

flow; in

the second

campaign

the sam

e m

odel propeller coated w

ith IS90 and tested behind non-uniform

flow as w

ell as the uniform flow

.

The com

parative results

of the

first experim

ental m

easurements,

which

were

analysed using

the ITTC

analysis

and correction procedure, presented as the net sound pressure level of the propeller against the centre frequencies for the uncoated and coated blades at the fully loaded and ballast conditions as reported by M

utton et al (2006). The com

parisons indicated that there was

some effect of the coating and the beneficial

effect appeared

limited

to the

broadband frequencies

and the

higher advance

coefficients. At sm

aller values of advance coefficients,

which

covered the

design advance coefficient, the uncoated propeller exhibited reduced noise levels com

pared to the coated one. In the discrete frequency range

there w

as hardly

any discernable

difference between the tw

o. As the cavitation

increased (as in the ballast condition) the difference betw

een the noise levels of the uncoated

and coated

propeller at

smaller

advance coefficient diminished.

The recent follow up investigations by

Korkut

and A

tlar (2009)

measured

the com

parative noise levels of the benchmark

model propeller, and analysed and presented

in the

similar

manner

to the

previous investigation. H

owever they used IS900 to

coat the blades and also included the effect of flow

non-uniformity by w

ake screen. Typical com

parative presentation

of their

measurem

ents in uniform flow

is shown in

Figure 14 for fully loaded condition. From

these measurem

ents it was concluded that

whilst the coating of the blades reduced the

noise levels in non-cavitating condition (i.e. higher advance coefficients, J=0.75-0.60), it slightly increased in the developed cavitation condition. This finding applied to both fully loading and ballast condition in uniform

and non-uniform

flows.

Interaction with bio-fouling

As stated earlier the effect of fouling is a

rather important but com

plex phenomenon

and hence to prevent and reduce the fouling

462

Specialist Comm


settlement

on any

surfaces, including

propeller blades, should be the prime target

rather than assessing or modelling of the

fouling effects.

Within

this fram

ework

numerous end-user-testim

onies and 4 years of m

onitoring of the New

castle University R

/V

Bernicia propeller reveal that FR

coating can effectively stay on blades m

ore than 3 years alm

ost 85-90% percent of the coating intact.

For example, Figure 14 show

s the state of the FR

coating (IS700) on the propeller of the earlier

mentioned

tanker vessel

after 37

months in service. D

uring this period the coating

has clearly

prevented the

major

fouling development except the slim

e fouling.

This beneficial

effect w

as even

more

obvious on the New

castle University R

/V

propeller as shown in Figure 15 w

here the uncoated

propeller (after

14 m

onths) is

compared

with

the FR

(IS700)

coated propeller (after 24 m

onths). It was noted that

the uncoated propeller was covered w

ith hard shelled barnacles that had to be rem

oved by abrasive m

eans or scrapers, Mutton et al

(2003).In contrast the slime or even barnacles

that may be attached to FR

coated surfaces could be rem

oved by pressure washing or

gentle sweeping action.

The effect of slime on any type anti-

fouling is a pretty well-know

n and complex

issue, and experience so far with FR

coatings indicates that this coating type suffers m

ore from

the slime com

pared to other types, since slim

e film w

ill attach more strongly to foul

release surfaces than other fouling organisms.

Experimental

studies w

ith FR

coatings

indicated that increasing the flow shear can

reduce the thickness of the slime layer but not

remove

completely,

e.g. K

lijsnstra et

al (2002). W

hile this may com

promise the initial

drag benefits of FR coatings, at higher speeds

that propeller blades operate, this benefit may

still persists due to thinner layer of slime film

as discussed by C

andries et al (2003). This is a rather topical issue currently attracting m

uch research supported by paint m

anufacturers and ship ow

ners.

In an

attempt

to m

odel the

coating roughness including the bio-fouling effect on ship resistance the recent study by Schultz (2007) is w

orthy to note. In this study the resistance-roughness characteristics of som

e coating types on flat surfaces, w

hich are exposed to different grades of roughness and bio-fouling (varying from

slime to heavy

calcareous types)

settled in

a controlled

environment, have been established by using

a similarity law

scaling procedure proposed by G

ranville (1958) and (1987) based on the sim

ilarity between sm

ooth and rough w

all boundary layers.

142

463


Figure 14. Effect of coating on noise levels of m

odel propeller for at varying advance coefficients in uniform

flow for fully loaded condition.

464

Specialist Comm


Figure 14. Face and back view

of the benchmark tanker propeller painted by IS700 FR

coating after 37 m

onths in service without any cleaning

Figure 15. R/V

Bernicia propeller uncoated after 14 m

onths in service (left); coated by IS700 after 36 m

onths in service without cleaning (right)

This procedure enabled Schultz to predict the

effect of

a given

roughness on

the frictional resistance of a plate of arbitrary length (i.e. representing ship surface) based on

laboratory-scale m

easurements

of the

frictional resistance and roughness function of a sm

aller flat plate covered with the sam

e roughness. Schultz applied this procedure to predict the roughness and fouling penalties of a U

S frigate demonstrating as high as 86%

penalty for the heavy calcareous fouling case.

Although this study is only representative and

requires further

proof, its

potential im

plication in assessing performance losses

due to deteriorated blade surfaces including various grades of bio-fouling can be plausible since the procedure is generic and technically can be applied to the blade sections based on the flat plate approach as applied in e.g. A

tlaret al (2002). H

owever further roughness data

of different types of coating in controlled environm

ent m

ay be

required for

the sim

ulation of typical propeller surfaces.

Concluding rem

arks

Propeller

coating has alw

ays been

interest to ship owners by m

ultiple

143

465


reasons am

ongst w

hich the

prevention/reduction of

galvanic corrosion and that of bio-fouling are the

well

recognised ones.

Recent

developments in foul release coating

technology and increasing number of

FR coated propellers indicates that

these coatings

have m

ost of

the desired

properties of

propeller coating

and currently

the m

ost suitable system

for development of a

propeller coating.

In spite of various anecdotal claim

s there has been no credible evidence from

full-scale to demonstrate any

gain/loss from a vessel fitted w

ith new

ly polished

propeller and

FR

coated one. How

ever there is limited

evidence that

these coatings

can provide

the propeller

surface w

ith roughness and texture levels sim

ilar to new

ly polished surfaces for a long tim

e after its applications. This will

provide savings

in propeller

efficiency and

maintenance

cost relative to the efficiency and cost of unpolished propellers in-service.

There is

no published

report of

dedicated trial or model test on the

comparative

efficiency, cavitation

and noise emission characteristics of

a propeller as uncoated and coated w

ith FR coatings apart from

a single source.

Limited

amount

of tests

conducted in

this source

with

a m

odel propeller with the coated and

uncoated blades have not revealed any

remarkable

difference in

the open

water


inception and extent as well as the

measured noise levels despite som

e sm

all variations

in these

characteristics due to the effect of coating.

Propeller m

odel tests

with

coated blades suffer from

appropriate paint thickness

at m

odel scale

due to

practical limitation of the application

method w

ith comm

ercial FR coatings.

This requires further investigations.

Sem

i-empirical expressions used for

the frictional

drag coefficient

of uncoated

propeller blade

sections need

to be

modified

to take

into account surface roughness effect of coated sections properly. This w

ill in turn

require drag-roughness

correlation studies with foul release

coated surfaces, preferably including the effect of slim

e.

V

alidation and

verification studies

involving m

odel and

full-scale perform

ance of coated propeller will

require standard

measurem

ent procedures and reliable m

easurement

tools, which are preferably optical

and practical to use in model and

full-scale, for

the m

easurement

of appropriate

blade surface

characteristics.

There

is a

need for

dedicated com

parative full-scale

trials and

observations to accurately assess the effect of coatings on the propeller efficiency,

cavitation and

noise em

ission.

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characteristics”, International

Workshop

on Marine R

oughness and Drag, R

.I.N.A

., London.

Candries, M

., Atlar, M

., Mesbahi, E., Pazouki,

K., 2003, “The m

easurement of the drag

characteristics of Tin-free Self-Polishing C

o-polymers

and Fouling

Release

coatings using

a rotor

apparatus”, Biofouling,19S.

Candries, M

and Atlar, M

., 2003, “On the

drag and

roughness characteristics

of antifoulings”, Intl. Journal of M

aritime

Engineering, RIN

A, Vol. 145, A

2.

Candries, M

., Atlar, M

., 2005, “Experimental

investigation of the turbulent boundary layer

of surfaces

coated w

ith m

arine antifoulings”,

Journal of

Fluids Engineering, A

SME, Vol 127.

I.T.T.C.,

1990, R

eport of

the Pow

ering Perform

ance Com

mittee, Proceedings of

the 19th

International Tow

ing Tank

Conference, M

adrid.

Candries, M

., Atlar, M

., Paterson, I., 1999, “C

avitation tunnel tests with coated m

odel propeller”,

Marine

technology report,

University of N

ewcastle.

Atlar, M

., Glover, E.J., C

andries, M., M

utton, R

., Anderson, C

.D., 2002, “The effect of a

Foul R

elease coating

on propeller

performance”,

Conference

Proceedings Environm

ental Sustainability

(ENSU

S). U

niversity of New

castle.

Burrill,

L.C.,

1955-56, “The

optimum

diam

eter of

marine

propellers: A

new

design approach”, Trans. N

.E.C.I.E.S., Vol.

72.

Atlar,

M.,

Glover,

E.J., M

utton, R

., and

Anderson, C

.D., 2003, “C

alculation of the effects of new

generation coatings on high speed

propeller perform

ance”, 2

nd Intl

Warship C

athodic Protection Symposium

and

Equipment

Exhibition, C

ranfield U

niversity, Shrivenham.

Mutton,

R.J.,

Atlar,

M.,

Dow

nie, M

., A

nderson, C.D

., 2005, “Drag prevention

coatings for

marine

propellers”. 2nd

International Sym

posium

on Seaw

ater D

rag Reduction, B

usan, Korea.

Korkut,

E. and

Atlar,

M.,

2009, “A

n experim

ental study into the effect of foul release coating on the efficiency, noise and cavitation characteristics of a propeller”, SM

P’09, Trondheim.

Atlar M

., Unal B

., Unal, U

.O., Sam

pson R,

Politis, G., 2010. “WP5.2 H

ydrodynamic

Testing- Executive

Summ

ary”, A

MB

IO

Project Report, D

eliverable 5.2b1.

AM

BIO

, 2010,

Official

website,

http://ww

w.ambio.bham

.ac.uk/, A

pproached Decem

ber 2010.

Mutton, R

.J., Atlar, M

., Paterson, I., Sampson,

R., 2003, “The Effect of a Foul R

elease C

oating on the Research Vessel B

ernicia”, R

eport MT-2003-048, School of M

arine Science

and Technology,

University

of N

ewcastle.

468

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Mutton,

R.J.,

Atlar,

M.,

Dow

nie, M

., A

nderson, C.D

., 2005, “Drag Prevention

Coatings

for M

arine Propellers”.

2nd International

Symposium

on

Seawater

Drag R

eduction, Busan, K

orea.

Mutton,

R.J.,

Atlar,

M.,

Dow

nie, M

., A

nderson, C.D

., 2006, “The effect of a foul release coating on propeller noise and cavitation”

Advance

materials

and coatings sym

posium, R

INA

, London.

Klijnstra,

J.W.,

Overbeke,

K.,

Sonke, H

., H

ead, R. and Ferrari, G.M

., 2002, “Critical

speeds for fouling removal from

a silicone coating”, 11th International congress on m

arine corrosion and fouling, San Diego.

Candries, M

., Atlar, M

. and Anderson, C

.D.,

2003, “Estim

ating the

Impact

of new

-generation

antifoulings on

ship perform

ance: The

Presence of

slime”.

Journal of

Marine

Engineering and

Technology, Part A, Procs. IM

arEST, (A2).

Schultz, M

. P.,

2007, “Effects

of coating

roughness and

biofouling on

ship resistance

and pow

ering”, B

iofouling, 23:5.

Granville,

P.S., 1958,

“The frictional

resistance and turbulent boundary layer of rough surfaces”. Journal of Ship R

esearch 2: 52-74.

Task

3: R

eview

the existing

measurem

ent m

ethods for

surface roughness at m

odelscale and at full scale

3.1. Roughness Param

eters

Surface roughness in general is a measure

of the

of the

texture of

a surface.

It is

quantified by the vertical deviation of the real surface from

its ideal form; in case of large

deviations we speak about a rough surface.

Roughness values can either be calculated on

a profile or on a surface. Profile roughness param

eters (Ra, R

q….) are m

ore comm

on w

hereas area

roughness param

eters (Sa,

Sq,….) give m

ore significant values.

There are

many

different roughness

parameters in use, but R

a (Rah) is by far the

most com

mon one. Since these param

eters reduce all of the inform

ation in a profile to a single num

ber great care must be taken in

applying and interpreting them.

The following table gives an overview

over

the m

ost com

mon

formulas

how

to calculate roughness. Each of the form

ulas listed in the table assum

es that the roughness profile has been filtered from

the raw profile

data and the mean line has been calculated.

The roughness profile contains n ordered, equally spaced points along the trace w

here yi

represents the vertical distance from the m

ean line to the i th data point.

145

469


The m

ost com

monly

used roughness

parameter is the A

verage Hull R

oughness param

eter Rah representing the m

ean of all the vessel’s hull roughness readings.

The standard roughness unit is the peak to trough height in m

icrons per sample (one

sample is of 50 m

m length of the underw

ater hull).

3.2. M

easurement T

echniques

For the measurem

ent of roughness stylus instrum

ents and optical instruments are in use.

In the shipbuilding industry the BM

T Sea

Tech H

ull R

oughness A

nalyser (a

stylus instrum

ent with a surface probe) is accepted

as the industry standard instrument for the

measurem

ent of hull roughness.

470

Specialist Comm


3.3. Full Scale Measurem

ents

The hull roughness normally is m

easured in the w

ay that the hull is divided into 10 equal sections w

ith 10 measurem

ents each, 5 on the port and 5 on the starboard side. A

total

of 50 readings are taken on each side, 30 on the vertical sides and 20 on the flats. From

the 100 m

easuring locations, the Average H

ull R

oughness is calculated.

3.4. R

oughness Measurem

ents on Ship Models

Roughness m

easurements on ship m

odels are carried out (e.g. MA

RIN

, SSPA) but the results of the

measurem

ents are used for quality assurance and not for further investigation. M

ost of the Model B

asins do not measure the roughness of the m

odel’s hull. T

ask 4: Propose m

ethods that take into account surface roughness and other relevant characteristics of coating system

s; check the need for changes to the existing extrapolation law

s.

This chapter will outline recom

mendations

regarding procedures

in m

easuring skin

friction on

rough surfaces

aimed

at the

maritim

e sector.

1.M

easurement equipm

ent

Several different techniques can be used for m

easuring skin friction on rough surfaces som

e better suited than others. In no specific order the follow

ing can be mentioned:

Flat plate in towing tank

Flat plate in cavitation tank

146

471


Flat plate in open water channel

Pipe friction device Flow

cell C

ouette cell O

ther shapes than flat plate in towing

tank or the like such as ax symm

etric body or m

odel ship Full scale tests

1.1.Flat plate in tow

ing tank

In the

comm

ittees opinion

the best

combination

of accuracy

and com

plexity. U

sually a quite large surface can be coated, and if care is taken w

ith the setup and rigging of

the plate,

reproducibility is

usually excellent.

The longer and thinner the plate is the better, as skin friction resistance ratio to total resistance w

ill increase with those param

eters. Tow

ing speed is limited (to usually around

5m/s)

which

does require

some

more

extrapolation to full scale than for instance cavitation tank.

Re-rigging after a new

surface has been applied

can be

quite sensitive,

therefore control of reproducibility is very im

portant. Tim

e between tow

s can also be important as a

flat plat (especially if towed horizontally) is

sensitive to small changes to angle of attack

caused by vortical flow rem

aining in the tow

ing tank after a test.

1.2.Flate plate in C

avitation tank

Skin friction measurem

ents can be achieved by tw

o methods.

1.2.1.

Floating element m

easurements

A plate is built w

ith the sample coated on

the plate (and/or before the plate), with a very

small gap betw

een the measurem

ent plate and the

flush surrounding

plate. This

plate is

suspended in such a way that it is fixed, but

shear forces can recorded, usually by strain gauges.

To avoid edge effects the gap is critical, and step changes in roughness should be avoided by coating before and after the test section.

1.2.2.Boundary layer m

easurements

Measuring

the boundary

layer by

for instance LD

V (Laser D

oppler Velocim

eter), the velocity shift in logarithm

ic boundary layer can be recorded.

where

U+

is the

non-dimensional

wall

velocity, y+ the w

all distance and is the

velocity shift function, also known as the

roughness function. Critical is the extraction

of the friction velocity u� and several m

ethods have been proposed. This com

mittee has no

recomm

endations regarding which one to use.

472

Specialist Comm


Figure 4: V

elocity profile measurem

ents on different rough surfaces

Once

the velocity

shift function

is established by boundary layer m

easurements,

it relates to the skin friction coefficient as

where s and r refers to sm

ooth and rough respectively. Therefore for all boundary layer m

easurements

(and skin

friction m

easurements in general) it is im

portant to m

easure the hydraulically smooth case. The

above equation

is a

simplification

of integration

of the

log-law

boundary layer

equation, and assumes that the displacem

ent thickness is constant. D

epending on the type of m

easurement, care m

ust be taken to either ensure that the assum

ption holds, or otherwise

correct for the simplification. For boundary

layer measurem

ents for example m

omentum

or outer sim

ilarity methods can be used, but

will not be described further in this report, see

for example.

Finally, skin friction can be related roughness by the non-dim

ensional roughness height

or if boundary layer measurem

ents are not available (as for instance tow

ed plate or floating elem

ent measurem

ents)

The above equations can be used for any type

of skin

friction m

easurements,

the difference betw

een boundary layer methods is

that friction velocity is used directly, whereas

resistance m

easurements

should use

the second version of the equation. B

oundary layer measurem

ents are very time

consuming

and requires

expensive and

sensitive measurem

ent equipment. B

ut better control of displacem

ent thickness is possible than indirect m

ethods.

1.3.Pipe Friktion M

easurements

Pipe friction measurem

ents is probably the m

ost cost

effective m

ethod along

with

Couette C

ell flow. It is also w

ell suited for tests w

ith for example bio fouling as the test

147

473


pipes can

be transported

relatively easy

between test site and fouling site.

Measurem

ent m

ethod is

indirect as

measured param

eters is average flow velocity

and pressure drop over test section. Accuracy

is much low

er than for instance towed flat

plate however for surfaces w

ith high skin friction increase it is deem

ed sufficient (as for instance barnacle surface). B

oundary layer is not free (confined by the pipe radius) and correction to flat plate skin friction m

ust be perform

ed.

1.4.Flow

Cell

Mainly m

entioned to include types of tests. Flow

cell is not well suited skin friction

measurem

ents within the m

aritime sector as

Reynolds num

ber is very low and requires too

extensive extrapolation

to full

scale skin

friction.

1.5.C

ouette Cell

Couette

cell is

relatively sim

ple in

construction and build cost. It does however

produce results which is difficult to interpret

accurately due

to m

ainly the

formation

Taylor-Couette cells, com

plex axially non-uniform

boundary layer and boundary layer developm

ent, but

also issues

such as

increasing w

ater tem

perature during

tests.

Therefore, some difficulty exists calculating

Cf based on torque m

easurements, but [A

rcapi, 1984] suggested

w

here � is the von Karm

an constant and Re

h is the R

eynolds number based on the gap

length between cylinders.

Advantage w

ith Couette cells is that it is

rather easy

to apply

a new

surface,

and especially

for tests

which

require m

easurements over long tim

e (for example to

test self polishing) Couette cell is w

ell suited.

1.6.O

ther shapes

Generally

using other

shapes than

flat plate for tow

ing, seems like an unnecessary

complication in m

odel scale. The goal of skin friction

measurem

ents is

to acquire

skin friction lines w

hich can be extrapolated to full scale. U

sing for example a ship m

odel will

introduce m

uch higher

residual and

wave

resistance than for a flat plate, but even more

important

large variations

of skin

friction locally due to accelerating flow

around the m

odel. This makes it difficult to interpret

extracted increase in resistance. It is therefore not a recom

mended procedure.

2.Test Procedure R

ecomm

endations

2.1.R

eynolds Num

ber

It m

ust be

ensured that

the R

eynolds num

ber is sufficiently high. The lower the

Reynolds num

ber the higher the risk is that the surface becom

es hydraulically smooth.

This is the case no matter w

hat measurem

ent equipm

ent is being used.

Theoretically, the surface is hydraulically sm

ooth when y

+ is lower than 5. If this is the

case the Reynolds num

ber is too low for

measuring any effect related to skin friction

(exceptions does exist as for example ribblets

or active surfaces), and results will be of very

questionable value.

There is another reason to keep Reynolds

number

relatively high

which

is that

the results w

ill require less extrapolation to full scale. C

f smooth can be taken from

any source, for exam

ple Cf,ITTC .

474

Specialist Comm


2.2.

Flow speed

At least 2m

/s above hydraulically smooth

must be tested. If not it w

ill be difficult to perform

regression

analysis and

extract param

eters such as efficiency for the given surface. Ideally points should be fairly dense for m

ore confidence in regression analysis, but also to identify possible problem

s with the

test equipment/m

easurement m

ethod.

For some test equipm

ent this can present a problem

, especially

in a

towing

tank. Therefore it is recom

mended that it is possible

to fulfil

this recom

mendation

before tests

comm

ences.

2.3.R

eference surface

To be able to compare different surfaces

skin friction,

it is

imperative

that all

measurem

ents are completed w

ith reference to

a hydraulically

smooth

surface. M

ost m

easurements are unfortunately reference to

another rough surface, for example SPC

to silicone. This m

akes it impossible, or at the

very least quite difficult to collect results from

many different sources. Therefore at least one

measurem

ent must be carried through w

ith a hydraulic sm

ooth surface

where y

+=5 is the limit. This value w

ill for m

ost test setups be in the range 5-50�m, so

some polishing of for exam

ple a primer w

ill usually be necessary.

2.4.R

eproducability

Reproducability

will

vary quite

a lot

between

different m

easurement

equipment.

Two levels of reproducibility exists, w

ith and w

ithout re-rigging. A full ITTC

uncertainty analysis

would

be the

best procedure

to follow

, but at least for some m

easurement

techniques will require too m

uch additional w

ork.

Minim

um. R

epeat 3 measuring points 3 tim

es w

ithout re-rigging R

ecomm

ended. Same as test 1, but com

pleted tw

ice between re-rigging. R

e-rigging implies

that the setup is dismantled to a degree w

here a new

surface can be applied.

Reproducibility is param

ount, especially for testing for exam

ple coatings, as difference betw

een coatings and hydraulically smooth is

quite low (below

20% for m

ost cases and R

eynolds num

bers), betw

een m

ost com

mercial

coatings below

10%

. If

reproducibility is only 5% it w

ill have a significant im

pact on the analysis. M

any factors

can produce

low

reproducibility. This comm

ittee is aware of

the following error sources.

Towing tank: Poor alignm

ent of plate, too little tim

e between tests, suspension allow

ing plate to bend or Y

aw.

Cavitiation tank: N

ot stiff enough floating elem

ent increasing gap size, test section not flush

with

surroundings, scatter

in LD

V

measurem

ents. Pipe

friction device:

Reproducability

in m

easurement of average flow

velocity, non-flush pressure tap. C

ouette cell: Temperature change betw

een and under tests

2.5.Surface

Two aspects of the surface m

ust be considered

Application

Roughness height (and possibly other

parameters)

Application of com

mercial coatings m

ust be com

pleted in a fashion similar to the

procedure at

the shipyard.

For instance,

temperature

and hum

idity range

from

the supplier m

ust be followed, if high pressure

spray system is required the surface topology

and roughness height can change significantly from

the intended if a low pressure system

or roller is used.

148

475


The comm

ittee agrees that steel/primer

surface need not be considered. Even though a real untreated hull surface is not sm

ooth, applying

the coating

system

usually consisting of m

ultiple layers, most of the steel

roughness will be m

asked by the coating. This is off course not the case for w

elding seems

for example, but taking such im

perfections into account w

ill be practically impossible. A

further

(very sm

all) added

friction could

eventually be proposed.

Roughness

height m

easurement

should preferably

be com

pleted w

ith a

BM

T roughness analyser. H

owever, other devices

can be used, if they as a minim

um produce a

measure of R

a . MA

can perhaps add to this. O

ther param

eters can

be added

such as

average distance between roughness elem

ents for barnacles for instance. This m

ight be usefull at a later stage w

hen a relatively high num

ber measurem

ents are collected.

3.ITT

C R

ough Skin Friction D

atabase

It is

proposed that

an international

database of skin friction measurem

ents are created.

Many

different researchers

have m

easured skin friction on a lot of different surfaces seen on a ship hull. This includes coatings, bio-fouling and bio-film

s.

As no single facility w

ill have the funding available to test every coating, bio-fouling and bio-film

surface, the second best option is to

analyse results

following

the sam

e guidelines and procedures.

Tests have

been com

pleted w

ith test

equipment

as described

in section

1.1 at

varying Reynolds num

bers, facilities, surface size, roughness height m

easurement m

ethod (if any) and so forth. M

any tests are also referenced

to another

coating and

not a

hydraulically smooth surface.

It is therefore at present difficult to collect skin friction lines and present them

in the sam

e figure. For experiments w

hich fulfil the test procedure recom

mendations in chapter 2,

it will how

ever be possible to collect and com

pare the results.

3.1.Procedure

SSPA

and N

ewcastle

University

will

jointly be

responsible for

creation and

maintaining the hom

epage, and evaluate and present new

results.

After

submission

of results

hydro dynam

ist from either SSPA

or New

castle Uni.

will evaluate results subm

itted (see 3.2), and determ

ine if

results can

be used.

After

analysis is

completed

results w

ill be

publically available on the homepage.

3.2.

Submission of results

Any party can subm

it results completing

the submission form

and appending data in electronic

form.

At

a m

inimum

raw

m

easurement data and analysis to skin friction

coefficient m

ust be

supplied, along

with

description of analysis method.

Unless

requested otherw

ise all

material

submitted w

ill be publically available. It is assum

ed that at a minim

um the m

aterial can be used to extract necessary data by R

SFD

and present it together with other results.

RSFD

w

ill evaluate

the m

aterial in

accordance to items described in C

hapter 2, and decide a confidence level and w

hether or not results w

ill be added to the database. The subm

itter will have the option to com

ment on

the results before they are made public on the

homepage.

Skin friction line, velocity shift function param

eters and roughness height will be the

main publicised results com

pared to CF,ITTC .

All supplied m

aterial will be m

ade available on ftp server (or links to for exam

ple papers)

476

Specialist Comm


unless otherwise requested by the subm

itter in the subm

ission form.

3.3.

Analysis Procedure.

3.3.1.V

elocity shift function

If results are accepted the analysis procedure w

ill be as follows. V

elocity shift function

w

ill be used regressively on each skin friction line, how

ever using only one parameter (h)

will not be sufficient. Part of the ultim

ate outcom

e of SFRD

will be to specify the

efficiency param

eter for

various types

of surfaces.

Bow

den added

resistance m

ain shortfall is that it is based on a one param

eter description of the surface topology w

hich is not

sufficient as

can be

seen in

several articles.

Many different tw

o (and more) param

eter function have been investigated, but it is this com

mittees

conviction that

using an

additional parameter w

hich is not directly m

easurable by analysing the surface topology is the m

ost viable method. This additional

parameter is the efficiency param

eter. In stead of using

for description of the velocity shift as a function of roughness height, the efficiency param

eter C w

ill be introduced as

For each

measurem

ent added

to the

database either the velocity shift (boundary layer m

easurements) or C

f rough and smooth

and roughness height will be know

n and C

can be calculated (by least squares method

along the Reynolds num

ber range measured).

It is

the hope

that collecting

many

measurem

ents of different types of surfaces, for exam

ple silicone surfaces, will reveal a

fairly constant value of C, even w

ith varying roughness

heights. This

will

produce a

method

of calculating

the full

scale skin

friction using the roughness height and a type specific

efficiency param

eter, rendering

a m

uch more reliable m

ethod than the Bow

den added resistance used today.

Velocity

shift function

also have

the advantage that it can be used locally w

ith for exam

ple thin boundary layer methods or Elog

method for R

AN

S solvers.

3.3.2.C

omparison of results

The only reliable way to com

pare results from

different

institutions/measurem

ent m

ethods is to reference the measurem

ents to a surface w

ith known skin friction line. This

can in principle be any type of surface for exam

ple a

specific SPC

coating

applied exactly the sam

e way each tim

e. How

ever, the only practical procedure is to alw

ays use hydraulically sm

ooth surface.

As

residual resistance

(and w

ave resistance for som

e methods) is different for

each m

easurement

equipment

and design,

skin friction

lines cannot

be com

pared directly. Therefore, raw

results will be re-

evaluated using

the sm

ooth skin

friction m

easurements under the assum

ption that the only

resistance com

ponent that

changes betw

een tests of different surfaces is the skin friction.

Thus only

added skin

friction resistance w

ill be used The velocity shift function w

ill then be evaluated using a know

smooth skin friction

line such as CF,ITTC or other lines if deem

ed m

ore warranted.

149

477


This procedure

will

to a

large degree

remove

problems

with

comparing

results betw

een measurem

ent techniques at different facilities. It does require m

easurements of

hydraulically sm

ooth surface,

which

unfortunately is

not available

in m

any m

easurements.

It is

conceivable that

measurem

ents eventually can be added to the database using other reference surface, but several surface w

ith the correct reference line is necessary before such m

easurements can be added w

ith confidence.

Arpaci V.S., Larsen P.S., C

onvection Heat

Transfer, Prentice-Hall, Englew

ood Cliffs,

NJ, U

SA, 1984

Leer-Andersen M

., Larsson L., Andreasson H

., Skin

Friction M

easurements

on Rough

Surfaces and Full Scale evaluation, 2nd

International Sym

posium

on Seaw

ater D

rag Reduction, B

usan, Korea, 2005

Leer-Andersen

M.,

Larsson L.,

An

experimental/num

erical approach

for evaluating skin friction on full-scale ships w

ith surface

roughness, J.

Mar

Sci Technol, 2003

Conclusion and

Recom

mendations

1Extrapolation�M

ethods�

1.1Conclusions�

At this tim

e no evidence suggests that the recom

mendation

of the

25’th Specialist

Com

mittee

on Pow

ering Perform

ance Prediction regarding the use of the Tow

nsin roughness allow

ance should be revoked. This does not im

ply that the comm

ittee believes that Tow

nsin/Bow

den roughness allowance is an

accurate and universal roughness allowance,

but that at this point nothing better seems to be

available.

Based

on a

skin friction

model

test m

easurement

database a

new

or m

odified roughness

allowance

should be

suggested. C

onsidering the variety of surface roughness on a ship (coating, dam

age, slime, fouling) it is

likely that this new form

ulation will either be

several formulations or at least one form

ulation but w

ith roughness type dependent parameters.

A m

ost likely candidate for an improved

roughness allow

ance is

the velocity

shift function

(Roughness

Function), used

to generate B

owden or Tow

nsin type formulation

for the full scale ship using CFD

analysis supported by experim

ental and full-scale data.

All antifoulings suffer from

micro-slim

e (slim

e) even in newly applied condition. Foul

release coating particularly suffers from slim

e effect

due to

their non-biocidal

defence m

echanism w

hich requires shear stress to keep slim

e free.

There is

a lack

of data

on the

drag-roughness correlation of A

F-coatings as well as

of a new generation of self-polishing types to

improve the perform

ance extrapolations not only for the “as new

ly applied” (trial) condition but also for the “after som

e time” (in-service)

condition. Limited drag-roughness correlation

studies indicate that the skin friction of “newly

applied” foul release coated surfaces does not correlate w

ith single hull roughness parameters.

1.2

Recomm

endations

It will not be possible to generate a new

form

ulation without an extensive database of

skin friction measurem

ents. A relatively sm

all num

ber of existing datasets which is the basis

for all

formulations

today does

not lend

credibility to a new form

ulation which can be

used with higher confidence.

There is a need for investigation to establish a

relationship betw

een the

drag-roughness characteristics of surfaces coated either w

ith foul

release coatings

or w

ith the

new

478

Specialist Comm


generation of

self-polishing coatings

to im

prove the performance extrapolations. These

investigations should be extended for coated surfaces

“in-service” as

the surface

characteristics of coatings change progressively in service, particularly in case of self-polishing coated surfaces. A

lthough this is a challenging task it is the reality in predicting pow

er in-service.

There is

need for

data concerning

the roughness-drag correlations of flat plat plates coated w

ith foul release as well as w

ith the m

odern day

self-polishing type

coatings. Investigations to collect appropriate data are required.

The effect of micro scale biofouling (slim

e) on the paint perform

ance should be included in the

performance

predictions and

hence investigations should be w

idened to cover this effect w

hich is a hot issue in foul release coatings.

2Model�Test�Procedures�

2.1

Conclusions�

The most accurate m

ethod for skin friction m

easurements probably is the flat plate in the

towing

tank, but

several other

methods,

including boundary layer measurem

ents, can produce valid results.

Tests should be carried out at Reynolds

numbers

which

produce a

flow

above the

“hydraulically smooth surface” to have any

meaningful results. For com

parison with other

experiments it is of high im

portance that a reference

surface is

tested w

hich is

hydraulically over the Reynolds range. If this is

not the case it is impossible to com

pare tests com

ing from different facilities.

Reproducibility should be tested especially

for equipment w

hich needs to be re-installed w

hen changing the surface, e.g. in case of a flat plate in tow

ing tank. Reproducibility w

ith and w

ithout re-installing should be checked.

Roughness

measurem

ent should

as a

minim

um include R

a. Including more surface

parameters such as R

t, profile measurem

ents and so forth adds value to the m

easurements.

Foul release

coated surfaces

suffer from

inaccurate m

easurements in full-scale (as w

ell as in m

odel-scale with relatively large surfaces)

with

stylus type

mechanical

surface m

easurement devices.

2.2 Recom

mendation

Regarding future w

ork one issue which this

comm

ittee feels can progress the confidence and accuracy greatly for roughness allow

ance and

its application

range is

to establish

a com

parative database

for skin

friction m

easurements.

Initially as much data as possible follow

ing the recom

mendation for test procedure at least

to an extent should be collected and compared

after which alternative roughness allow

ance

3Propeller�Coatings�

3.1 Conclusions

Propeller coating

has alw

ays been

of interest to ship ow

ners by multiple reasons

amongst w

hich the prevention and/or reduction of galvanic corrosion and that of biofouling control

are w

ell recognized.

Recent

developments

in foul

release coating

technology and an increasing number of coated

propellers indicates that this paint technology has m

ost of the desired properties of propeller coating

and is

currently the

most

suitable system

for development of a propeller coating.

In spite of various anecdotal claims there

has been no credible evidence from full-scale

measurem

ents to prove any gain or loss from a

vessel fitted with a coated propeller com

pared to

a new

ly polished

uncoated propeller.

How

ever there is limited evidence that the foul

release based

coatings can

provide the

propeller surfaces with roughness and texture

levels sim

ilar to

newly

polished uncoated

surfaces and even better for a long time after its

applications. There is also evidence that these

150

479


coatings can maintain the blade surface free

from m

ajor fouling for long time w

ithout any m

aintenance. This suggests potential savings in propeller

efficiency and

maintenance

cost relative to the efficiency and cost of unpolished propellers in-service.

There is no published report of dedicated trials

or m

odel tests

on the

comparative


and noise

emission

characteristics of

a propeller

uncoated and

coated with foul release coatings apart from

a single

source. Lim

ited am

ount of

tests conducted w

ith model propellers w

ith coated and uncoated blades have not revealed any rem

arkable difference in open water efficiency,

cavitation inception and extent as well as the

measured

noise levels

despite som

e sm

all variations in these characteristics due to the effect of coating.

Propeller model tests w

ith coated blades suffer

from

appropriate paint

thickness in

model scale due to application m

ethods with

comm

ercial coatings. A

lthough this

conclusion applies

to any

coating, as

a generic

problem

of the

foul release

type coatings,

any validation

and verification investigation involving the m

odel and

full-scale perform

ance of

foul release

coated propeller

will

require a

standard m

easurement

procedure and

reliable m

easurement

tools for

the surface

measurem

ents. 3.2

Recomm

endations

There is

growing

number

of full-scale

applications and

an increasing

interest on

propeller coatings.

Investigations therefore

should continue in this field.

There is a need for dedicated model tests,

full-scale trials

and progressive

docking observations to accurately assess the effect of coatings on the propeller efficiency, cavitation and noise perform

ance. At least lim

ited amount

round robin tests for open water perform

ances am

ongst the ITTC com

munity m

ay resolve som

e current model test related issues.

As a generic problem

of the foul release type coatings, investigations on the application and

measurem

ent of

coatings on

model

propellers (and full-scale) should continue with

the objective of devising standard procedures and resolving the scale effect issue involving paint thickness.

Semi-em

pirical expressions

used for

the frictional drag coefficient and perhaps the lift coefficient of uncoated blade profiles need to be m

odified to take into account the coating effect.

As

a generic

problem

of any

coating applied surface the technology investigation of coatings should be extended for the effect of biofouling, at least for the effect of slim

e which

is the natural conditioner of any coating but particularly affecting the perform

ance of foul release coatings.

4State�of�the�Art�Coatings�

4.1 Conclusions

Anti fouling technology is under further

scrutiny due to environmental concerns. A

s a result, although currently in sm

all proportion, the applications of foul releasing (non-biocidal) type

antifoulings are

increasing w

orldwide

requiring further attention and hence further investigation.

Solid evidence comparing the skin friction

characteristics between m

ajorities of coatings is non-existing.

Different

model

evaluation, application and m

easuring techniques make it

very difficult to compare m

easurements for

which reason m

ost of the measurem

ents are only able to state that this coating is xx%

better than another coating. 4.2

Recomm

endation

Measurem

ents of hull surfaces coated with

foul release surfaces in dry docks suffer from

“contact” problems of stylus in m

echanical devices. Furtherm

ore, a single hull roughness param

eter is not sufficient to characterize the

480

Specialist Comm


measured surfaces. There is a need for the

development

of “non-contact”

based m

easurement

devices providing

options for

more param

eters and hence investigations in this areas should continue

Appendix:

ITTC Skin Friction Data Subm

ission Form

Com

pany/in

stitution

P

hon

e

Con

tact person

A

dress

e-mail

Su

bmission

date

Appen

ded

material (raw

data, analysed data, reports, papers)

File nam

e (description)

Pu

blic (Yes/n

o) 1. 2.

3. Test descrip

tion

1. Equipment (see docum

ent XXX, section 1.1, 1-8). If other please specify

2. Reynolds num

ber range

3. Flow speed range

4. Roughness height m

easurement type (device and param

eter)

Short description of test equipment if not standard

Su

rfaces tested

Deliverables D

escription

R

ough

ness h

eight

Oth

er parameters

1. (name or description)

2.

3.

Additional information

151

1

ON

T

HE

IMP

OR

TAN

CE

OF A

NT

IFOU

LING

ST

HE

IMP

OR

TAN

CE

OF A

NT

IFOU

LING

SFO

RG

RE

EN

SH

IPS

Byy

Prof. M

ehmet A

tlar

1

Main objective of antifoulings

P

reventing the attachment of fouling and

hence min

imisin

gd

rag is the m

ain objective of m

arine antifoulings(A

/F)

Im

proved drag redu

ces fuel co

nsu

mp

tion

and in turn G

HG

emissio

n

T

here are other ways of keeping sh

ip h

ulls

clean but none so far proven to be viable for

thevastm

ajorityof

thew

orld’sfleet

the vast majority of the w

orlds fleet

K

eeping ship

s’ pro

pellers free o

f fou

ling

is also im

portant from the ship perform

ance point of view

2

Antifouling econom

ies –S

PC

Coatings

Indirect reduced costs (e.g. bunker transport)1080M

$/y

Reduced dry docking costs

800M $/y

Extended docking intervals409M

$/y

Reduced fuel cost

720M $/y

TOTAL

SAVING

3,000M $/year

EA

RLY

1990s data, A

. Milne

3

Impact on G

HG

emission –

SP

C C

oatings

NO

x

•2%

saving due to sm

oother hulls

•2%

saving due to

GH

G

&

CO

xS

Ox

improved antifouling

performance

•A

nnual fuel saving: 7.4 M

tonnes

•R

ate of CO

2em

ission:3.1 ton / Ton-F

uel

Ozon

Depleters

•Total C

O2 saving:

20M tonnes / year

EA

RLY

1990s data, A

. Milne

4

152

2

Antifouling –

Current drivers

Ever increasing and unpredictable fuel prices; financial clim

ate

Ship operators are looking at cost m

ore closely than ever

IM

O and N

ational Legislationsg

S

hip operators have A/F

high on the agenda by law

-IM

O/A

FS

Convention (O

ctober 2001)

N

ew coating technologies and associated products

B

iocidal/ Hybrid/ N

on-biocidal; Ship operators are confused by the claim

s and counter claim

s regarding to A/F

The environm

ent matters m

ore than everO

ttt

bi

tll

lit(IS

O)

O

perators w

ant to be environmentally com

pliant (ISO

)

S

hips have to be energy efficient by design (EE

DI) and operation (E

EIO

) –IM

O-M

EP

C 58-59 report on “IM

O G

HG

Study 2009” (A

pril 2009)

N

oise unsteadiness due to fouling during operations needs separate study –IM

O-M

EP

C 59/19 C

orrespondence Group report “N

oise from com

mercial

shipping and its adverse impacts on m

arine life“ (April 2009)

5

Antifouling technology options

CD

P1.

Biocidaloption

C

ontrolledD

epletionP

olymer

(CD

P)

TBT free SPC

Controlled D

epletion Polym

er (CD

P)

S

elf-Polishing C

opolymer (S

PC

)

H

ybrid SP

C

2.N

on-biocidaloption

Foul R

elease (non-stick)

Hybrid SPC

Foul Release

6

Biocidaloptions

Currently 90%

of the world fleet use these products

Hybrid SPC

ERFORMANCE

SPC“S

elf-Polishing C

opolymer”

PRIC

E

PE

CD

P“C

ontrolled Depletion P

olymer”

7

Non -biocidaloption

Potential fuel savings

Currently less than 10%

of the world fleet use this product

Foul Release

No biocides

Low VO

C

and lower em

issions

Durable &

Long lasting

Less weight

Antifouling Performance

Lower M

&R

costs

Less paint

Keeps fouling off propellers

8

153

3

Current R

& D

needs

There is in

creasing

interest and applications of fo

ul release co

ating

s due to their environm

ental and other benefits.

Relative m

erits of these coatings, especially for drag

ben

efits on hulls and propellers, need further R

&D

including:p

p,

g

T

o d

eve

lop

a ro

bu

st, ind

ustry b

ase

d d

evic

e to

me

as

ure

rou

gh

ness ch

ara

cteristics

of h

ulls a

nd

pro

pe

llers co

ate

d w

ith F

R p

ain

ts in d

ry do

cks an

d la

bs

T

o e

stab

lish n

ew

sk

in fric

tion

da

ta b

ase

an

d h

en

ce ro

ug

hn

ess a

llow

an

ce

asso

ciate

d w

ith th

ese

coa

ting

s for p

ow

er e

stima

tion

s

F

ou

l rele

ase

coa

ting

s ap

pe

ars to

be

mo

re v

uln

era

ble

to s

lime

gro

wth

tha

n b

iocid

al

coa

ting

s. Th

eir d

rag

pe

rform

an

ce in

the

pre

sen

ce o

f slime

effe

ct sho

uld

be

eva

lua

ted

i

il

dl

df

lll

tti

filiti

usin

g s

pe

cia

l mo

de

l an

d fu

ll sc

ale

tes

ting

fac

ilities

R

ea

l pe

rform

ance

eva

lua

tion

of h

ulls a

nd

pro

pe

llers w

ith d

iffere

nt co

atin

gs n

ee

ds

de

dica

ted

full-sca

le tra

ils with

sp

ec

ial p

erfo

rma

nc

e m

on

itorin

g d

ev

ice

s o

n b

oa

rd

F

ou

l rele

ase

coa

ting

s can

take

ad

van

tag

e o

f na

no

-en

gin

ee

red

surfa

ce p

atte

rnin

g th

at

can

be

furth

er e

xplo

ited

for d

rag

be

ne

fits with

clo

se

co

llab

ora

tion

be

twe

en

c

he

mis

t, ma

rine

bio

log

ist a

nd

hy

dro

dy

na

mic

st

at th

e d

eve

lop

me

nt sta

ge

of th

ese

co

atin

gs

9

Current R

& D

examples

N

ew B

MT

-H

RA

using laser sensor

Stylus based B

MT

-HR

A

La

ser se

nso

r ba

sed

prototype BM

T –

HR

A

10

Current R

&D

Exam

ples

New

BM

T-H

RA

deviceLaser profilom

eter

11

Current R

&D

Exam

ples

A

unique facility, which is fu

lly-turbulent flow channel (FLO

W C

ELL), h

as

been established to study the adhesion and friction drag characteristics of foul release coatings in

the presence of marine bio-fouling, in particular

“slime”

FLOW

CELL

Measuring

section size (L

x B x H

)

2.3m x 0.25m

x 0.01m

Contraction

ratio25:1

Max w

atervelocity

13.4 m/s

velocity

Max

shear stress

256kPa

Testslide

capacity14 slides

76mm

x 26mm

or

single plate 185m

m x76m

m

Operating

medium

Fresh/sea

water

at 280C

-300C

12

154

4

Current R

&D

Exam

ples

A

nother facility to investigate the service performance of S

PC

coatings is “AG

ING

FLUM

E” which sim

ulates the polishing activity in laboratory condition using seaw

ater in fully turbulent flow condition.

Measuring section length (m

)3.35

Measuring section w

idth (m)

0.4M

easuring section height (m)

0.02D

evelopment length (m

)1.5

Num

ber of plates6

Size of coated area/plate L×B (m

)0.6 x 0.28

Water velocity (m

/s)10

Water flow

rate (m3/h)

287M

aximum

wall shear stress (Pa)

167

Um

ean (m/s)

τw(Pa)

211

548

787

10167

13

T

here is a need for field data on service perform

ance of coatings using

“removable

testpatches”

Current R

&D

Exam

ples

using rem

ovable test patches

and novel ideas for “in-situ m

easurements” (e.g. using

rese

arch

vessels fitte

d w

ith special equipm

ent).

S

uch test (re

sea

rch) vesse

ls w

ith the state-of-the-art f

iti

tperform

ance monitorin

g syste

ms

(including thrust gauge) will

make m

ore realistic contribution into analysis of hydrodynam

ic perform

ance of different coatings

14

AM

BIO

(Advanced Nanostructure Surfaces for the C

ontrol of Biofouling)

wa

s an

E

U-F

P6

Inte

gra

ted

Pro

ject. T

he

5-ye

ar p

roje

ct com

ple

ted

in 2

01

0 w

as h

igh

ly in

terd

isciplin

ary in

clud

ing

na

no

tech

no

log

y, po

lyme

r scien

ce, su

rface

scien

ce, co

atin

g

tech

no

log

y, hyd

rod

yna

mics a

nd

ma

rine

bio

log

y. Pro

ject in

teg

rate

d 3

1 P

artn

ers fro

m

ind

ustrie

su

nive

rsities

an

dre

sea

rcho

rga

nisa

tion

an

dsig

nifica

nt

en

du

sers

invo

lved

Current R

&D

Exam

ples

ind

ustrie

s, un

iversitie

s an

d re

sea

rch o

rga

nisa

tion

an

d sig

nifica

nt e

nd

-use

rs invo

lved

A

pp

roxim

ate

ly 500 different foul release nano-structured coatings, re

pre

sen

ting

64

g

en

eric co

atin

g ch

em

istries w

ere

pre

pa

red

at la

bo

rato

ry-scale

an

d e

valu

ate

d fo

r the

ir a

ntifo

ulin

g a

nd

fou

l rele

ase

pe

rform

an

ce. O

f the

se, 15 w

ere down-selected

for testing in

a ra

ng

e o

f field

an

d e

nd

-use

r tests. S

eve

ral co

atin

gs sh

ow

ed

pro

mise

in

the

se tria

ls, an

d h

ave

eith

er b

ee

n co

mm

ercia

lized, o

r ha

ve th

e p

ote

ntia

l to b

e so

afte

r fu

rthe

r de

velo

p. 5 novel coatings w

ere patented.

Som

e of these coatings showed great potential fo

r dra

g re

du

ction

cha

racte

ristics for

hu

llan

dp

rop

elle

ra

pp

licatio

ns

eg

Flu

orin

ate

dsilico

ne

ble

nd

sa

nd

na

no

hyb

ridso

lg

el

hu

ll an

d p

rop

elle

r ap

plica

tion

s e.g

. Flu

orin

ate

d silico

ne

ble

nd

s an

d n

an

o-h

ybrid

sol-g

el

coa

ting

s with

clay n

an

ofillle

rs, resp

ective

ly.

ww

w.am

bio.bham.ac.uk15

A

KZ

O 19 (F

lourinatedS

liconeblend) displayed

favourableskin friction over m

ajor comm

ercial brands and patented by IP

0.0034

Current R

&D

Exam

ples

Cf (B)

0.0028

0.003

0.0032

AK

ZO19

Cf (B)

AK

ZO20

Cf (B)

AK

ZO21

Cf (B)

AK

ZO28

Cf (B)

INT900

Cf (B)

STEELC

f (B)

Re

500010000

1500020000

0.0024

0.0026

16

155

5

Current R

&D

Exam

ples

Ch

em

ists

MA

RIN

E

AN

TIF

OU

LING

Ma

rine

B

iolo

gists

Sh

ip

Ow

ne

r

Na

val

Arch

itect

17

THA

NK

YOU

THA

NK

YOU

Sh

lf

School of M

arineScience and Technology

mehm

[email protected]

marine@

newcastle.ac.uk18

156

ITTIC資料

2010年４月16日

ITTIC資料

防汚塗料について防汚塗料について

日本ペイントマリン㈱山盛直樹

船底防汚塗料の現状船底防汚塗料の現状

157

アリストテレス：船低に“Echeniis”が付着すると船速が低下BC.400

防汚の歴史

船底の汚損防止にピッチ、蝋、タール、アスファルトを使用

キメデ船底に鉛を用銅ボト締める

BC.300～200

アルキメデス：船底に鉛を用い、銅のボルトで締める

レオナルド・ダビンチ熔融鉛を船底の汚損防止用に使用

BC 287～212

ﾙﾈｻﾝｽ時代

生物付着防止用に船底を銅板で被服（特許）1625年

船底を虫食いから防止するためタールを塗装（船底塗料の最初の特許）

英国艦隊はすべて銅板で覆う

1685年

1776年英国艦隊はすて銅板で覆う

鉄船の時代に入る ⇒ ＡＣ塗料の出現

1776年

19世紀

光明社創設

日本特許第1号「錆止め塗料及びその塗り方」1885年

1881年

日本特許第1号「錆止め塗料及びその塗り方」1885年

代表的な付着生物（１）

158

代表的な付着生物（２）

代表的な付着生物（３）

159

防汚塗料の組成防汚塗料の組成

樹脂（塩化ゴム・加水分解型アクリル樹脂樹脂（塩化ゴム加水分解型アクリル樹脂

・ロジン等）

可塑剤

体質顔料体質顔料

着色顔料

添加剤（タレ止め剤沈降防止剤等）

防汚塗料

添加剤（タレ止め剤・沈降防止剤等）

防汚剤防汚剤

溶剤

船底塗料の世界的動向（有機スズ防汚剤規制）

2001年10月の国際海事機構（IMO）外交会議での有害な防汚

方法の規則に関する国際条約が採択された方法の規則に関する国際条約が採択された。

１．2003年1月1日以降すべての船舶に殺生物剤として機能す

る有機スズ化合物（ﾄﾘﾌﾞﾘﾙｽｽﾞ化合物、ﾄﾘﾌｪﾆﾙｽｽﾞ化合物）

を含有する防汚塗料の塗装の禁止

２．2008年1月1日以降すべての船舶の船体外部表面に殺生物剤

として機能する有機スズ化合物を含有する防汚塗料の存在の禁止

（ブラストし非有機スズ船底塗料に塗り替え、シーラーコート

で有機スズ船底塗料を被服する。）

160

船底塗料の法的規制

- 船底塗料はBiocidal Productsとして分類される。- Biocidal products は殺虫剤／殺草剤のような規制を受ける。p

分解分解

塗膜表面の防汚剤

海水中の防汚剤海水中防汚剤

堆積物中の防汚剤分解分解

環境に対する３つのポイント:

防汚剤の分解速度付着生物以外の生態の毒性付着生物以外の生態への毒性生体蓄積性

防汚剤の種類

防剤名No. CAS. No. 防汚剤名

1 1111-67-7 ロダン銅

2 1317-39-1 亜酸化銅化

3 137-30-4 Ziram (P

4 330-54-1 DCMU (Preventol A6)

5 971 66 4 P idi t i h lb (PK)5 971-66-4 Pyridine-triphenylborane (PK)

6 1085-98-9 Dichlofluanid ((Preventol A4)

7 13108-52-6 Tems pyridine (Densil S-100)

8 13167-25-4 Trichlorophenyl-maleimid（IT-354）

9 13463-41-7 Zinc pyrithione

10 14915-37-8 Copper pyrithione10 14915-37-8 Copper pyrithione

11 28159-98-0 Irgarol 1051

12 64359-81-5 Seanine-211

13 1897-45-6 Chlorothalonil

14 12122-67-7 Zineb

15 137-26-8 Thiram15 137 26 8 Thiram

161

付着生物と防汚剤

動物 TBT Cu 防汚助剤

外殻をもつものフジツボセルプライガイ

外殻をもたないもの

イガイ

ヒドロホヤ

植物ホヤ

緑藻藻類緑藻褐藻紅藻

藻類

“緑色スライム"“黒色スライム"

珪藻類

防汚剤登録（日本塗料工業会）

2004年以降2004年以降

「IMO・2001年の船舶に有害な防汚方法の規制に関する

国際条約への適合性に関する（社）日本塗料工業会自主

管理登録品」管理登録品」

として登録および情報公開

162

船底塗料国登録

登録が必要な国々登録が必要な国々

アメリカカナダ

スウェーデンオランダ

アイルランドベルギーアイルランドベルギー

フィンランドオーストリア

マルタホンコン

オーストラリアニュージーランドオーストラリアニュージーランド

船級登録

船舶の安全航行における環境負荷の低減

Lloyd

Germanischer Lloyd

DNV

KRKR

をはじめとする各船級への登録をはじめとする各船級への登録

163

船底塗料の分類 LF-Sea（低摩擦）

船底塗料分類

加水分解型

自己研磨型A/F

（低摩擦）

自己研磨型A/F

水和分解型

SPC(従来型）

溶出型崩壊型A/F 燃費

拡散型A/F（溶出型A/F)

費

表面物性

非溶出型忌避非溶出型忌避

電気的等

自己研磨型樹脂の特徴

+

海水中

《樹脂が親水化・溶出》加水分解

70

（平均運行速度：２０ノット）

ＫＬ/510浬

セルフポリッシング（自己研磨作用）

Insoluble spot60

拡散型塗膜

費燃

料

Insoluble spot

消耗膜厚

50

消費消耗膜厚

121110987654321040

自己研磨型塗膜

基盤

図　運行燃費節減効果

経過月数

運航後の塗膜の断面写真164

加水分解機構

Ｙ

銅アクリル樹脂

C=O

OCu

O

C=O++

XY ＋＋

C=O

O O

RＸ（海水：PH=8.2)

海水中に溶出

O

Cu

海水中に溶出O

C=O

R

加水分解型（＝自己研磨型）塗料用樹脂加水分型磨型塗用

有機錫アクリル樹脂銅／亜鉛アクリル樹脂シリルアクリル樹脂

O

C=O C=O

O

C=O

R RBu BuSn

O O

Me

O

Sｉ

RBu O

C=O

R

M C ZMe： Cu or Zn

165

各種錫フリー船底塗料の特徴（溶出型）

塗装直後経時表面変化

加水分解型A/F

水和分解型・崩壊型A/F崩壊型A/F

拡散型A/F

(μg/cm2 /day)

50

60

u]

拡散型

40

50

出速度[Cu 拡散型

（塩化ゴム/ロジン）

20

30

防汚

剤放出

自己研磨型（SPC)

10

20

が着

２４６８ 1210

測定期間（月）

0

生物が付着する放出量

測定期間（月）

図防汚剤（Ｃｕ 2Ｏ）の放出速度

166

スズフリー自己研磨型樹脂

（比較的古いタイプの樹脂）

シリルアクリル樹脂銅アクリル樹脂亜鉛アクリル樹脂

C=O

O

C=OC=O

OO

Cu

O

iPr iPrＳｉ

O

Zn

O

C=O

iPrO

C=O

R R

（当社塗料には使用しておりません）

新規加水分解型樹脂（HyB）シリルアクリル樹脂A/Fの難点を克服するため、従来の

金属含有アクリル樹脂技術を組み合わせ新規樹脂を開発ハイブリッド化樹脂

シリル・銅アクリル樹脂銅アクリル樹脂シリルアクリル樹脂

＋C=O C=O

C=O

O

C=O

＋O

Cu

O

iPr iPrＳｉ

O

Cu

O

iPr iPrＳｉ

O

C=O

iPr O

C=O

iPr

C O

RR

167

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