Leeboard

A Dutch sailing barge showing its stowed windward leeboard, hiked up with wind from starboard

Leeboard deployed on aThames sailing bargeon theEast Swin

The Centenniala 1979 Ted Brewer sharpie fitted with leeboards

Aleeboardis a form of pivotingkeelused by a sailboat largely and very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like acentreboard,allowing shallow-draft craft to ply waters fixed keel boats cannot. Only theleewardside leeboard is used at any time, as it submerges when the boatheelsunder the force of the wind.

A 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. The classical, archetypal definition of ballast is a low, central weight to optimisecentre of mass,reduce turning moment and therefore resistance to the boat keeling over, however tends to be higher in self-righting vessels. Modern developments allow them to act as a speed-enhancingliftingfoil.

History

See also:Naval history of China

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".Leeboards for stabilizingjunksand improving their capability to sail upwind, are documented from a book by Li Chuan. The innovation was transmitted to Portuguese and Dutch ships around 1570."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."

Leeboards have been used by relatively large inshore and coastal sailing vessels used for transport since 1570, such asDutch barges,Thames barges,and Americangundalows.For these boats, leeboards provided the advantages of shallow draught for working close inshore and an unobstructed hold for cargo. In particular, they allowed gundalows to take the hard to load and unload cargo in unimproved tidal areas, as well as readily conduct maintenance on their hulls. Leeboards were also easier to build than a large centreboard would have been.

Today

Leeboards are no longer common in commercially-built boats, because many people consider them inelegant and awkward. They are far more common in home-built boats, especially thePuddle Duck Racerandstitch and gluetype sailboats. Leeboards simplify construction of thehull,as they are attached to the outside and do not require holes in the hull, which can leak. Since centreboards are retractable, they require a large, watertight trunk to hold them in place when retracted, and this occupies what otherwise might be useful space in thecabinorcockpitof the boat. Use of leeboards, while it adds complexity to the process of tacking, leaves the floor of the boat unobstructed.

According to traditional design principles, a boat utilizing a leeboard either needs to have two retractable leeboards, one on each side, or a method of removing the leeboard and attaching it to either side while under way, because nearly all sailboatstackto work their way upwind (with the exception of theproa). However, some small sailboat designers claim to have created seaworthy vessels with only a single, fixed leeboard.

On a traditional two-leeboard (or non-fixed leeboard) design, the boards are designed so that thewindwardboard can be retracted, to reducedrag.Unlike centreboards, which are symmetric along the boat's axis, leeboards are often asymmetric, so that they more efficiently provide lift in one direction.Some fast racingscowsusebilgeboards,which are mounted between the centreline of the hull and the sides, so they can use a pair of asymmetric foils for maximum lift and minimum drag.

See also

• Bruce foil