The balanced rudder was an innovation in warship construction first used in HMS Bellerophon (1865). HMS Bellerophon was a Victorian central battery ironclad battleship of the Royal Navy; she was a major step forward in design technology as compared to previous classes in terms of engine power, armament, armour, hull design and seaworthiness. ...

Overview

In ships previous to the Bellerophon, whether military or civilian and whether driven by power or by sail, the rudder was a simple flat piece of wood or metal, situated at the after end of the hull and hinged at the forward end, which could be angled to one side or the other to deflect the water passing it and hence provide an impulse to turn the ship. This required the exertion of significant force, as the passage of the water past the rudder tended to force it into a straight line in conformity with the flow. Three ships of the British Royal Navy have been named HMS Bellerophon after the mythological Greek hero Bellerophon. ... The worlds oldest depiction of a rudder. ...

The concept of a balanced rudder involved the shifting of the centre of rotation of the rudder to point approximately one-third of the way from the forward end to the after end. This meant that when the rudder was turned, the flow of water past the ship actively worked on the forward third to increase the angle of deflection, whereas the same flow acted on the after two thirds to reduce the angle. The mechanics of fluid dynamics produced a solution in which the turning force applied in one direction on the rudder by the passing water was balanced by the turning force applied in the other direction, allowing the rudder to be moved with only limited mechanical resistance. Fluid dynamics is the subdiscipline of fluid mechanics that studies fluids (liquids and gases) in motion. ...

References

Oscar Parkes British Battleships ISBN 0-85052-604-3