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Q8. A ship of 30800 tonne displacement has a length of 150 m, breadth of 26.5 m and floats at a draught of 10.5 m when in sea water of density 1025 kg/m³.

The ship’s propeller has a diameter of 6.5 m with a pitch ratio of 0.8.

When the propeller is operating at 1.75 revs/sec, the real slip is 32% and the thrust power is 6800 kW.

The thrust power is reduced to 5500 kW and the real slip increases to 35%. It can be assumed that the thrust power is proportional to (speed of advance)³.

Calculate EACH of the following for the reduced power:

(a) ship speed; (11)

(b) the propeller speed of rotation; (3)

(c) the apparent slip.  (2)

Note:  Wake fraction = 0.5 C_b – 0.05