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Q6) The force acting normal to the centreline plane of a rudder is given by the expression:

F n =15.5 A V² α newtons

Where: A = rudder area (m²)

V = ship speed (m/s)

α = rudder helm angle(degrees)

A ship travelling at a speed of 20 knots, has a rudder configuration as shown in Fig Q6.

The centre of effort for areas A1 and A2 are 32% of the width from their respective leading edges. The rudder angle is limited to 35ofrom the ship’s centreline.

Fig Q6

Calculate EACH of the following:

(a) the diameter of rudder stock required for a maximum allowable stress of 77MN/m²; (12)

(b) the drag component of rudder force when the rudder is put hard over at full speed. (4)