Q6. A single screw ship with a service speed of 15 knots is fitted with a rectangular rudder, 5.5 m deep and 3.5 m wide, with its axis of rotation 0.4 m from the leading edge.
At a rudder helm angle of 35 degrees, the centre of effort is 32% of the rudder width from the leading edge.
The force on the rudder normal to the plane of the rudder is given by the expression:
F = 577 A v2 sin α (newtons)
Where: A = area of the rudder (m2)
v = ship speed (m/s)
α = rudder angle (degrees)
The maximum stress on the rudder stock is to be limited to 70 MN/m2.
Calculate EACH of the following, for a rudder angle of 35 degrees:
(a) the minimum diameter of the rudder stock for ahead running; (9)
(b) the speed of the ship, when running astern, at which the maximum stress level would be reached. (7)
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