A centreboard (UK) or centerboard (US) is a retractable keel which pivots out of a slot in the hull of a sailboat, known as a centreboard trunk (UK) or centerboard case (US). The retractability allows the centreboard to be raised to operate in shallow waters, to move the centre of lateral resistance (offsetting changes to the sailplan that move th... Found on http://en.wikipedia.org/wiki/Centreboard
• (n.) 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 ... Found on http://thinkexist.com/dictionary/meaning/centreboard/
(from the article `keel`) The backbone keel may be supplemented by other keels (see Figure). A `centreboard`also called a drop keel, or sliding keelis a retractable keel ... Found on http://www.britannica.com/eb/a-z/c/45
An adjustable fin primarily used to stop the boat moving sideways through the water. Also called daggerboard. Found on https://www.encyclo.co.uk/local/21233