A leeboard is a lifting

Lift (force)

A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 foil

Foil (fluid mechanics)

A foil is a solid object with a shape such that when placed in a moving fluid at a suitable angle of attack the lift is substantially larger than the drag...

 used by a sailboat, much like a centerboard, but located on the leeward side of the boat. The leeward side is used so that the leeboard isn't lifted from the water when the boat heels, or leans under the force of the wind.

History

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 have been used by relatively large inshore sailing vessels used for transport since 1570, such as Dutch barge

Dutch barge

Dutch barges are flat bottom boats, originally used for cargo carrying in the Netherlands, many of which have now been converted for pleasure or residential use. Originally made of wood and powered by sail, most of the existing barges are made of iron or steel and powered by diesel engines...

s and Thames barges

Thames sailing barge

A Thames sailing barge was a type of commercial sailing boat common on the River Thames in London in the 19th century. The flat-bottomed barges were perfectly adapted to the Thames Estuary, with its shallow waters and narrow rivers....

. For these boats, leeboards provided the advantages of shallow draught for working close inshore and an unobstructed hold for cargo. They were also easier to build than a large centreboard would have been.

Current designs

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 the Puddle Duck Racer

Puddle Duck Racer

A Puddle Duck Racer or PD Racer is an 8 foot long, 4 foot wide, 16 inch high, spec series, racing sailboat or day sailer. It is a one design hull shape with wide options in other areas. Billed as "the easiest sailboat in the world to build", the scow hull is a simple box, usually built of...

 and stitch and glue

Stitch and glue

Stitch and glue is a simple boat building method which uses plywood, epoxy glue, and "stitches" and eliminates the need for stems and chines. Plywood panels are cut to detailed profiles and stitched together to form an accurate hull shape, without the need for forms or special tools...

 type sailboats. Leeboards simplify construction of the hull

Hull (watercraft)

A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

, as they are attached to the outside and do not require holes in the hull, which can leak. Since centerboards 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 the cabin

Cabin (ship)

A cabin or berthing is an enclosed space generally on a ship or an aircraft. A cabin which protrudes above the level of a ship's deck may be referred to as a "deckhouse."-Sailing ships:...

 or cockpit

Cockpit (sailing)

In the Royal Navy, the term cockpit originally referred to the area where the coxswain was stationed. This led to the word being used to refer to the area towards the stern of a small decked vessel that houses the rudder controls...

 of 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 sailboats tack to work their way upwind (with the exception of the proa

Proa

A proa, also seen as prau, perahu, and prahu, is a type of multihull sailing vessel.While the word perahu and proa are generic terms meaning boat their native language, proa in Western languages has come to describe a vessel consisting of two unequal length parallel hulls...

). 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, they are designed so that the windward board can be retracted when it isn't needed to reduce drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

. Unlike centerboards, which are symmetric along the boat's axis, leeboards are often asymmetric, so they more efficiently provide lift in one direction only. Some fast racing scow

Scow

A scow, in the original sense, is a flat-bottomed boat with a blunt bow, often used to haul bulk freight; cf. barge. The etymology of the word is from the Dutch schouwe, meaning such a boat.-Sailing scows:...

s use bilgeboard

Bilgeboard

A bilgeboard is a lifting foil used in a sailboat, which resembles a cross between a centerboard and a leeboard. Bilgeboards are mounted between the centerline of the boat and the sides, and are almost always asymmetric foils mounted at an angle to maximize lateral lift while minimizing drag...

s, which are mounted between the centerline of the hull and the sides, specifically so that they can use a pair of asymmetric foils for maximum lift and minimum drag.

External links

• PDRacer.com Puddle Duck Racer - The Easiest Boat In The World To Build