Balanced rudder

The balanced rudder was an innovation in warship construction first used in HMS "Bellerophon", which was launched in 1865.

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.

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.

References

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