Skeg

A fixed longitudinal projection beneath the hull that provides directional stability or protects and supports underwater gear.

A skeg may extend ahead of a rudder, support the lower rudder bearing, protect a propeller, or form part of the aft keel profile. On some planing craft and outboard or stern-drive legs, the term is also used for a smaller fin below the propeller gearcase.

Its exact function depends on the design. Grounding damage can affect alignment, steering, seals or nearby structure even when the visible deformation appears small.