Q8. (a) The residuary resistance of a 1/25 scale model of a ship is 7.65 N when tested at 1.75 m/s in fresh water of density 1000 kg/m³. The frictional resistance of the ship at 15 knots in sea water of density 1025 kg/m³ is 185 kN.
Frictional resistance can be assumed to vary with speed to the power 1.825. Calculate the effective power (naked) for the ship at the speed corresponding to the model test. (8)
(b) The following additional data apply to the ship operating in service at the corresponding speed as calculated in Q6(a), with a propeller having a pitch of 4.75 m.
Appendage and weather allowance = 23%
Quasi-propulsive coefficient (QPC) = 0.71
Propeller speed = 1.9 revs/sec
Taylor wake fraction = 0.33
Propeller thrust = 640 kN
Calculate EACH of the following:
(i) the torque delivered to the propeller; (3)
(ii) the propeller efficiency; (3)
(iii) the real slip ratio. (2)
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