Cofficents of forms are used to understand the shape or configuration of ship and dimensions of the ships.These are dimension less quantity.
Waterplane Coefficient (Cw): It is the water plane area divided by multiplication of length and breadth.
Cw = Aw / B*L
Aw -Area of water plane
B - Breadth
L - Length
> High Cw indicates good stability, good maneuverability in rough conditions and high frictional resistance.
>Low Cw indicates low frictional resistance and fine ends
Midship Coefficient (Cm): It is the cross sectional area of under water portion of the midship section to the product of breadth and draught
Cm= Am/BT
Am - Midship section cross section area of immersed portion
B - Breadth
T - Draught
> It gives an idea of shape of the ship at the mid ship
>Cargo vessels having boxy shape at mid section because of high Cm where as Sail boats having low Cm
Block Coefficient (Cb): It is the ratio of volume displaced by the ship to the product of length, breadth and draught of the immersed portion of the ship.
Cb= ∇/LBT
∇ - Volume of displacement
L -Length of immersed portion
B- Breadth of immersed portion
T- Draught
Prismatic Coefficient (Cp): It is the underwater area, divided by the area of a midship section and the length of the ship
Cp= ∇/AmL
∇ - Volume of displacement
Am -Area of immersed portion of midship section
L -Length of immersed portion
Relation between Cp,Cb and Cm
Cb=CpxCm
Cw = Aw / B*L
Aw -Area of water plane
B - Breadth
L - Length
> High Cw indicates good stability, good maneuverability in rough conditions and high frictional resistance.
>Low Cw indicates low frictional resistance and fine ends
Midship Coefficient (Cm): It is the cross sectional area of under water portion of the midship section to the product of breadth and draught
Cm= Am/BT
Am - Midship section cross section area of immersed portion
B - Breadth
T - Draught
> It gives an idea of shape of the ship at the mid ship
>Cargo vessels having boxy shape at mid section because of high Cm where as Sail boats having low Cm
Block Coefficient (Cb): It is the ratio of volume displaced by the ship to the product of length, breadth and draught of the immersed portion of the ship.
Cb= ∇/LBT
∇ - Volume of displacement
L -Length of immersed portion
B- Breadth of immersed portion
T- Draught
> Under water volume of ships are calculated using block coefficient
>Tankers having high Cb Passenger vessels having lower block coefficient Prismatic Coefficient (Cp): It is the underwater area, divided by the area of a midship section and the length of the ship
Cp= ∇/AmL
∇ - Volume of displacement
Am -Area of immersed portion of midship section
L -Length of immersed portion
Relation between Cp,Cb and Cm
Cb=CpxCm