Page 273 - Introduction to Naval Architecture

258 MANOEUVRING

Figure 10,2 Ship heeling in turn

and rudder are F h and F r, acting at KH and KR above the keel
then:

and the heeling moment is:

For most ships (KH- KR) will be small and the heeling moment
becomes (F k - F r) GH. This leads to an angle of heel such that:

This is only an approximation to the angle as it is difficult to
estimate the centre of lateral resistance for a heeled hull. In
some high speed turns the heel can be quite pronounced. It is
important in passenger carrying ships and may influence the
choice of metacentric height.

The zig-zag manoeuvre

A ship does not often turn through large angles and seldom through
even a half circle. Thus the turning circle is not realistic in terms of
movements of a ship in service. It is also difficult to measure the initial
reaction to the rudder accurately in this manoeuvre. On the other
hand a ship does often need to turn through angles of 10° to 30°. It is