Centerboard

{ Cen″ter‐board′, Cen″tre‐board, } (–bōrd′), n.(Naut.) A movable or sliding keel formed of a broad board or slab of wood or metal which may be raised into a water-tight case amidships, when in shallow water, or may be lowered to increase the area of lateral resistance and prevent leeway when the vessel is beating to windward. It is used in vessels of all sizes along the coast of the United States