centerboard

A centerboard is a type of retractable keel used on small sailing craft to balance draft and stability while providing lateral resistance when sailing upwind. It consists of a watertight blade mounted on a centerline trunk, which can be lowered into the water or raised into the hull or a housing.

Most centerboards are designed to pivot about a fulcrum or slide within a trunk; lowering is controlled by a line, winch, or equivalent mechanism, and on larger boats may be hydraulically actuated. The board’s foil shape is chosen to maximize lateral resistance with minimal drag, and its position affects the boat's balance and hull efficiency.

Advantages include a shallow draft for beaching and launching, easier grounding in shallow waters, and the ability to optimize performance for downwind versus upwind points of sail. When lowered, it provides lateral resistance and contributes to initial stability; when raised, draft is reduced, allowing operation in shallow waters and easier trailering.

Disadvantages include added weight, mechanical complexity, potential for jamming, and reduced righting moment compared with a fixed keel. Performance depends on board area, shape, and alignment with the hull; improper trimming can increase drag or cause instability in rough seas.

Centerboards are common on many dinghies and daysailers, especially crafts designed for shallow waters. They are contrasted with daggerboards, which slide vertically in a trunk but do not pivot, and with swing keels or fixed keels.