<P> A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other conveyance that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw and p - factor and is not the primary control used to turn the airplane . A rudder operates by redirecting the fluid past the hull (watercraft) or fuselage, thus imparting a turning or yawing motion to the craft . In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail, or after end . Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag . On simple watercraft, a tiller--essentially, a stick or pole acting as a lever arm--may be attached to the top of the rudder to allow it to be turned by a helmsman . In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels . In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics . </P> <P> Generally, a rudder is "part of the steering apparatus of a boat or ship that is fastened outside the hull", that is denoting all different types of oars, paddles, and rudders . More specifically, the steering gear of ancient vessels can be classified into side - rudders and stern - mounted rudders, depending on their location on the ship . A third term, steering oar, can denote both types . In a Mediterranean context, side - rudders are more specifically called quarter - rudders as the later term designates more exactly the place where the rudder was mounted . Stern - mounted rudders are uniformly suspended at the back of the ship in a central position . </P>

What does a rudder do on a boat