Page 280 - Introduction to Naval Architecture

MANOEUVRING 265

Figure 10,6 Unbalanced rudder

Special rudders
A number of special rudders have been proposed and patented over
the years. The aim is usually to improve the lift to drag ratio achieved.
A. flap rudder, Figure 10.8, uses a flap at the trailing edge to improve the
lift by changing aerofoil shape. Typically, as the rudder turns, the flap
goes to twice the angle of the main rudder but in some rudders the
flaps can be moved independently. A variant is the Flettner rudder which
uses two narrow flaps at the trailing edge. The flaps move so as to assist
the main rudder movement reducing the torque required of the
steering gear.