4-S6

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

There is quite, a variety in the shapes of rudders, both in the ordinary
and balanced types. With the increased speed and size of modern
ships more and more attention is being given to the streamline shaping
of rudders and the methods of their suspension with a view to reducing
the resistance offered by the rudder to the vessel's forward motion.,
The whole area of an ordinary rudder (Fig. 54) is abaft its turning axis,

iA

GEAR

Fig. 59. Fig. 60. Fig. 61.
and the "centre of pressure" exerted by the mass of water impingeing
against It is a point somewhere between the middle of its breadth and the
forward edge. This point alters in position with the angle of helm and
is approximately about one-third the breadth of the rudder abaft the
pintles. Considerable power is therefore needed to turn' it, and sp
balanced rudders are fitted in fast ships having large rudders and where
quick rudder movements are required.