Q6. The force acting normal to the plane of a rudder is given by the expression:
Fn = 20.17 Av2α newtons
Where: A= rudder area (m2)
v = ship speed (m/s)
α = rudder angle (degrees
A manoeuvrability specification for a ship that requires a constant transverse rudder force of 75 kN is generated when the angle of helm is 35o with the ship travelling at a speed of 5 knots.
(a) Determine suitable dimensions for a rectangular rudder having a depth to width ratio of 1.6. (6)
(b) The rudder stock is designed to have a diameter of 320 mm with the allowable shear stress in the material limited to 70 MN/m2 at its service speed of 15 knots.
At the maximum helm angle of 35o the centre of effort is 34% of the rudder width from the leading edge of the rudder.
Calculate the distance of the axis of rotation from the leading edge of the rudder so that the stock is not overstressed at the service speed. (10)
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