A daggerboard is a retractable centreboard

Centreboard

A centreboard or centerboard is a retractable keel which pivots out of a slot in the hull of a sailboat, known as a centreboard trunk or centerboard case...

 used by various sailing

Sailing

Sailing is the propulsion of a vehicle and the control of its movement with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to move the boat relative to its surrounding medium and...

 craft. While other types of centreboard may pivot to retract, a daggerboard slides in a casing. The shape of the daggerboard converts the forward motion into a windward lift, countering the leeward push of the sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

.

Characteristics

Daggerboards are often long and thin, thus providing a better lift-to-drag ratio. Daggerboards are usually found in small craft such as day sailer

Day sailer

A daysailer, day sailer, or dayboat is a small sailboat with or without sleeping accommodations but which is larger than a dinghy. Dayboats can be monohull or multihull, and are typically trailer-able. Many dayboats have a small cabin or "cuddy" for storage and to provide a shelter, or for...

s, where their size is easily handled by a single person. Daggerboards are not usually ballasted, but are locked in place by a clip.

When a daggerboard is extended through the keel, it improves a ship's stability. Daggerboards can be raised when the a ship enters a shallow harbor, allowing the boat (for example) to load and unload cargo in locations that would not otherwise be accessible to larger ships.

If a daggerboard is located off center, then it is called a leeboard

Leeboard

A leeboard is a lifting foil 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....

 or a 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...

.

One problem with such boats if that if one were to hit shore, it would be quite easily damaged.

Boats equipped with it

The Mirror Dinghy, for example, uses a plywood daggerboard. The Laser

Laser (dinghy)

The International Laser Class sailboat, also called Laser Standard and the Laser One is a popular one-design class of small sailing dinghy. According the Laser Class Rules the boat may be sailed by either one or two people, though it is rarely sailed by two. The design, by Bruce Kirby, emphasizes...

 and Vanguard 15

Vanguard 15

The Vanguard 15 is a popular one design racing dinghy designed by Bob Ames. It is a double-handed monohull sailboat with a sloop rig . Ideally the combined weight of the crew is between 270 and and both members hike off the boat to keep it flat...

 also use daggerboards.

In 2008, a 55 feet (16.8 m) daggerboard ship was found in Lake Ontario

Lake Ontario

Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south by the American state of New York. Ontario, Canada's most populous province, was named for the lake. In the Wyandot language, ontarío means...

, using deep scan sonar equipment off the lake's southern shore, the only one known to have been found in the Great Lakes

Great Lakes

The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...

. Vessels of this type were used for a short time in the early 19th century.

According to
there are only four non-custom manufacturers of catamarans which use daggerboards: Catana, Outremer

Outremer

Outremer, French for "overseas", was a general name given to the Crusader states established after the First Crusade: the County of Edessa, the Principality of Antioch, the County of Tripoli and especially the Kingdom of Jerusalem...

, Sud Composites, and Dolphin. One reason might be its construction cost, estimated to be about $30,000 for a 45 feet (13.7 m) catamaran

Catamaran

A catamaran is a type of multihulled boat or ship consisting of two hulls, or vakas, joined by some structure, the most basic being a frame, formed of akas...

.