sternpost rudder

The sternpost rudder is a steering apparatus for boats and ships, typically attached to the sternpost outside the hull. It's usually a flat surface of wood or metal hinged at its forward edge. The rudder works by creating unequal water pressures. When turned, one side experiences more water force than the other, pushing the stern and changing the boat's direction.1

Early steering methods involved paddles or oars. Later, a steering oar was attached to the vessel's side. Rudders fixed to the sternpost became common after the 11th century. Larger vessels use machinery to turn the rudder, while smaller craft use a tiller or helm. Specialized rudders, like balanced or semibalanced types, are designed to ease steering pressure.1