70.Rudder types

Rudders are classified into three types.

1.Unbalanced
2.Semi-balanced
3.Balanced

Unbalanced rudder

It has all of its area aft of its axis of rotation, resulting a high torque on the steering gear, rudder stock and pintles.

Semi-balanced rudder

It has up to 20% of its area forward of its axis of rotation. This result in a lower torque on steering gear, rudder stock and pintles than unbalanced rudder. Modern semi-balanced rudders are L shape.

Balanced rudder

It has between 20% and 40% of its area forward of its axis of rotation. This not only results in a lower torque than semi-balanced rudder, but also means that at some rudder angle axis of rotation and centre of effort coincide. At this angle torque is zero and rudder is said to be fully balanced. This will usually occurs at a rudder angle about 15 deg.