Rudder

A steering surface that produces a turning force by deflecting water flowing past it.

A rudder may be hung on the stern, supported by a skeg, balanced around a stock, mounted as a spade or incorporated into other arrangements. It works only when there is sufficient relative water flow, which can come from vessel movement or propeller wash.

Large angles can stall the flow and increase drag without producing more turning force. Stock, bearings, pintles, gudgeons, seals, steering linkage and emergency tiller arrangements require inspection because damage or fouling can cause loss or restriction of steering.