Leeboards have been used by relatively large inshore and coastal sailing vessels used for transport since 1570, such as Dutch barges, Thames barges, and American gundalows. "The Portuguese experimented with caulking their vessels in the Chinese manner and the Dutch probably added leeboards to their craft that were copied from Chinese models." The innovation was transmitted to Portuguese and Dutch ships around 1570. Leeboards for stabilizing junks and improving their capability to sail upwind, are documented from a book by Li Chuan. Leeboards existed in China from at least the eighth century on warships that "held the ships, so that even when wind and wave arise in fury, they are neither driven sideways, nor overturn". Modern developments allow them to act as a speed-enhancing lifting foil. The classical, archetypal definition of ballast is a low, central weight to optimise centre of mass, reduce turning moment and therefore resistance to the boat keeling over, however tends to be higher in self-righting vessels. Only the leeward side leeboard is used at any time, as it submerges when the boat heels under the force of the wind.Ī disadvantage, where there is an inadequate fixed keel, is that they typically ship (bear) little ballast, which being on the far side delays the onset of unballasted craft's heeling, that is, to put up a good, constant resistance against the wind. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters fixed keel boats cannot. Sailboat pivoting keel A Dutch sailing barge showing its stowed windward leeboard, hiked up with wind from starboard Leeboard deployed on a Thames sailing barge on the East Swin The Centennial a 1979 Ted Brewer sharpie fitted with leeboardsĪ leeboard is a form of pivoting keel used by a sailboat largely and very often in lieu of a fixed keel.
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