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, n = 70%

Answer 1

Part (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

$$Thrust\:\left(T\right)\:=\:\rho\times A\times P^2\times n^2\times S$$

Where,

ρ - Density

A - Area

P - Pitch

n - Revolution per second

S - Slip

✓ Verified Model Answer (Text Solution)

Slip