Class 2 (2nd Engineer) SC&S 📅 Oct 2025

Exam Question

With reference to fixed pitch propellers:

(a) Explain Propeller Slip and Propeller thrust. (6)

(b) The shaft power of a ship is 3000 kW, the ship's speed V is 13.2 knot. Propeller rps is 1.27, propeller pitch is 5.5m and the speed of advance is 11 knots. Find: (10)

(i) Real slip

(ii) Wake fraction

(iii) Propeller thrust, when its efficiency, η = 70%

Reference Answer

(a) Slip is the difference between the theoretical distance the propeller should travel in one revolution and the actual distance the vessel travels.
$$Slip\:\left(\%\right)\:=\:\left(\frac{Engine\:distance\:-\:Ship^{\prime}s\:distance}{Engine\:distance}\right)\:\times100$$
Where Engine distance = no. of propeller revolutions * propeller pitch (usually calculated over a 24-hour period)
Propeller thrust: it is the force exerted by the propeller to move the vessel ahead and given by

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