Centre-board

The board which works on a thwartships pin up and down in the centre-board trunk, passing through a fore-and-aft narrow opening in the keel of the vessel. When the board is hoisted all the way up its lower edge is flush and parallel with the keel. When down the board drops a distance below the keel according to the size of the vessel. It is lowered to overcome the sideways drift (leeway) of the ship when she is close hauled.