Q4. ship of 7200 tonne displacement floats at a draught of 5.2 m in sea water of density 1025 kg/m3. Area of waterplane is 1600 m2, centre of buoyancy above the keel (KB) is 2.7 m and metacentric radius (BM) is 4.4 m. A centrally located rectangular midship compartment 25 m long and 10 m wide is now bilged, causing bodily sinkage to a new draught of 5.8 m. Calculate EACH of the following using the lost buoyancy method: (a) the permeability of the compartment; (4) (b) the change in transverse metacentric height due to bilging the compartment. (12)
Q6. A spade-type rudder has an area of 6.33 m2. At its maximum designed rudder angle of 35o, the centre of effort is 0.12 m aft of the axis of rotation and 1.6 m below the lower edge of the rudder stock bearing.
The force on the rudder normal to the plane of the rudder is given by the expression:
Fn=18.32 A v2 α newtons
where: A=rudder area (m2)
v=ship speed (m⁄s)
α=rudder angle ( degrees)
The equivalent twisting moment (TE ) is given by :
TE=M+ √(M2+ T2 )
where : M=bending moment
T=torque
The maximum stress in the rudder material is to be limited to 77 MN/m2.
Calculate EACH of the following:
(a) the diameter of the rudder stock required for a ship speed of 16 knots (10)
(b) the speed to which the ship must be restricted, given that the effective diameter of the stock is reduced by wear and corrosion to 375 mm. (6)
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