Download - Stability Presentasi
-
8/2/2019 Stability Presentasi
1/25
SHIP STABILITY
Amiruddin MayaMan Ops Meratus Lines
Surabaya, 05/05/2004
-
8/2/2019 Stability Presentasi
2/25
What
Stability is the tendency of a vessel toreturn to its original position after ithas been inclined due to externalforces.
-
8/2/2019 Stability Presentasi
3/25
Why
To analyze and review commercial andsafety decisions :> The allocation of cargos on specific vessel> Vessel Allocation Plan> Safety and seaworthy of the vessel
-
8/2/2019 Stability Presentasi
4/25
When
`Cargo booking exceeded of ship capacity> Nos of containers. > Weight of cargo.> Cargo type
`Ship Roll over / Change route
-
8/2/2019 Stability Presentasi
5/25
How
Assumptions standardsSimple spreadsheet calculation
-
8/2/2019 Stability Presentasi
6/25
Variables
Light ShipConstant
Ballast WaterFresh Water
FuelCargo
Free Surface
-
8/2/2019 Stability Presentasi
7/25
Main Factors
The condition of the vessel as regardsstability is determined almost wholly bythe location of three points in a vessel :
> Metacenter M > Center of Gravity G > Center of Buoyancy B
-
8/2/2019 Stability Presentasi
8/25
Metacenter M
The Metacentric height of the vessel depends uponthe vertical distance of two points above the keel.Every change of draft, the position of M changes and
effects stability. Theoretically, M start to move ofthe centerline as soon as a vessel inclines butpractically the movement is negligible for inclinations
up to 10 degrees or thereabouts depending uponthe form of the vessel.Therefore, M can safely be used as a point which
each is Vertically above G for small inclination
-
8/2/2019 Stability Presentasi
9/25
Center of Gravity G
Point at which allthe vertically
downward forces ofweight of the vesselcan be considered
to act. Or it is thecenter of the mass ofthe vessel
G
-
8/2/2019 Stability Presentasi
10/25
50
G
100 100
?
10
30
40
-
8/2/2019 Stability Presentasi
11/25
Center of Gravity G
When a vessel is inclined due to someexternal force, that is by the action of
seas. G will remain fixed in its locationin the vessel. Of course if weight arefree to move on the vessel, G will move
too but for the time being, it is assumedthat G does remain in its originalposition
-
8/2/2019 Stability Presentasi
12/25
Center of Buoyancy B Point at which all thevertically upward
forces of support(buoyancy) can beconsidered to act.
Or it is the centerof volume of theimmersed portion of
the vessel.
B
-
8/2/2019 Stability Presentasi
13/25
Center of Buoyancy B
When a vessel is inclined,the B will move since is
it the center of volume ofthe immersed portion ofthe vessel, and the wedgeof buoyancy has beentransferred from one sideof the vessel to otherside
B B
-
8/2/2019 Stability Presentasi
14/25
The Couple
A couple is formed whenever two equalforces are acting on a body in oppositeDirections and along parallel lines.
G
B
-
8/2/2019 Stability Presentasi
15/25
The Couple
G Z
B B
Why doesthe move center of BuoyancyWay from its position directly under center of Gravity cause a Righting Tendency ??
-
8/2/2019 Stability Presentasi
16/25
Righting Moment
The tendency of vessel to return to an erect position(called stability) can be determined for all angles ofinclination, by the value of the righting moment,
w x GZ, or solely by the length of the righting arm,For small angles of inclination, or initial stability, itcan be determined by the distance that G is from M,or metacentric height. In order to find GM it isnecessary to find KG and KM. Where the value ofKM is not available it may be necessary to calculateit by finding KB and BM
-
8/2/2019 Stability Presentasi
17/25
Righting Moment
M
ZG
B B
Q
-
8/2/2019 Stability Presentasi
18/25
Stable Equilibrium
G
BB
Z
M
-
8/2/2019 Stability Presentasi
19/25
Neutral Equilibrium
G M
BB
-
8/2/2019 Stability Presentasi
20/25
Unstable Equilibrim
G
M
B
B
-
8/2/2019 Stability Presentasi
21/25
Free Surface
G
G
M
g g
-
8/2/2019 Stability Presentasi
22/25
Free Surface
Whenever the surface of liquid within avessel is free to move, the condition knownas free surface is present. The effects ofFree Surface on transverse stability sincean excessive amount of free surface caneasily change a vessel with a positive GMinto one with a negative GM.
-
8/2/2019 Stability Presentasi
23/25
> The effects of free surface depend upon thedimensions of the liquid and the volume of displacement of the vessel
> The effect of free surface depend to minor degreeupon the relationship between the specific gravityof the liquid in the tank and the specific gravity of the liquid in which the vessel is floating
> The effect of weight and vertical position of theliquid have an effect on transverse stability whichis not associated with free surface effect
Free Surface
-
8/2/2019 Stability Presentasi
24/25
AbbreviationG : Gravity
B : BuoyancyM : MetacenterVCG : Vertical Center of GravityLCG : Longitudinal Center of Gravity
TPC : Ton per CentimetreMTC : Moment to Change TrimKG : Height of center of GravityKB : Height of center of Buoyancy
KM : Metacentric HeightLCB : Longitudinal Center of BuoyancyLCF : Longitudinal Center of FloatationFSM : Free surface moment
-
8/2/2019 Stability Presentasi
25/25
Abbreviation
Displacement: Total Dead weight plus Light shipLOA : Length Over AllLBP : Length Between PerpendicularDWT : Dead Weight Tons
Draft : Keel to WaterlineGRT : Gross Register TonnageNRT : Netto Register Tonnage