Finned centre-board used on boat - has fins angled, shaped, to match hull line fixed releasably or permanently along board bottom edge on both sides

摘要

The finned centreboard on a boat has fins of flat or curved sheet fixed lengthwise on both sides along the bottom edge of the - otherwise conventional - retractable centreboard. These fins are not perpendicular to the board. The fins may be connected releasably, by screws , or permanently by welding, rivetting or gluing, and their shape is harmonised with that of the hull. Materials used may be ferrous or non-ferrous. When the centreboard is lowered these fins may act like wingtip fences on an aircraft, to increase efficiency, or they may act as hydrofoil blades.