Daggerboard

A daggerboard is a retractable centreboard used by various sailing 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. The theoretical centre of lateral resistance is on the trailing edge of the daggerboard.

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 sailers, where their size is easily handled by a single person. Daggerboards are not usually ballasted, but are locked in place by a clip. They are raised vertically unlike a centreboard which can be set at different angles to the hull of the boat.

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.

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

If a daggerboard is located off center, then it is called a leeboard or a bilgeboard. An analog to a centerboard on a dinghy are bilgeboards (they exist in pairs, but are used singly) in a Scow.

The centerboard, daggerboard or bilgeboard can be used as a recovery platform upon which to stand, providing increased leverage, in the event the dinghy overturns via a capsize or turtle.

Boats with daggerboards

The Mirror Dinghy, Laser, and Vanguard 15 use a daggerboard.

In 2008, a 55-foot-long (17 m) daggerboard ship was found in Lake Ontario, using deep scan sonar equipment off the lake's southern shore, the only one known to have been found in the Great Lakes. Vessels of this type were used for a short time in the early 19th century.

According to one source there are only four non-custom manufacturers of catamarans which use daggerboards: Catana, Outremer, Sud Composites, and Dolphin. One reason might be its construction cost, estimated to be about $30,000 for a 45-foot (14 m) catamaran. However, there is a large number of custom and semi-custom catamaran builders who offer daggerboards as an option.

Catamarans are steady because of the multihull with daggerboards

Keel is vertically removable

A daggerboard is a vertically removable keel that travels through the hull of the rig along its center line usually in midsection. In the early 19th century daggerboards were rarely being used on schooners. A schooner is an American ship with two or more masses. These schooners were used for nearby coastal trade of cotton, wheat and apples. A sunken 1833 daggerboard schooner was found in the great lakes with the help of sonar equipment. Knowing this, daggerboards have been around since late the 17th century. Daggerboards can be found on monohulls which is the classic sailboat and multihulls called catamarans. During in an event which a sailboat flips on its side the keel can be used to up right it back where it belongs by standing on the keel while pulling the sail in your direction. Of course up righting a sailboat is easier with smaller rigs. Daggerboards come in all different shapes and sizes, some curved or s- shaped. Many high performance sailing vessels use curved or angled daggerboards to create vertical lift to reduce displacement. Some vessels with vertically lifting daggerboards are capable lifting their completely from the water while others only lift the hull partially from the water. Examples of sailing vessels with such daggerboards include the America's Cup yacht USA 17 (yacht) and James H. Clark's 100-foot Super-maxi, Comanche.

Purpose

The purpose of the daggerboard is to grip the water and keep the boat from being blown in the direction of the wind. It gives stability and provides lift. Lift is important so the nose of the rig rides up so it doesn’t drag as much through the water. Without a daggerboard the boat cannot go anywhere up wind. Generally daggerboards are used on smaller rigs such as 10 to 40 feet for racing. It mostly based off personal preference, whether or not you actually want a dagger board. Daggerboards are faster than fixed keels because fixed keels have so much hydrodynamic drag by the shape. The shape can resemble an airplane wing which is aerodynamic. Monohulls allow the sailor to tack much quicker than catamarans. Tacking is where a sailboat wants to go up wind, but it cannot go directly into the wind so It goes in a zigzag pattern till the destination is reached.

How it works

The daggerboard provides stability and lift. The force of a daggerboard depends on the length, width, and angle of the daggerboard. The daggerboard works as an opposite reaction of the force on the sails. Because the water is a lot denser than air, the larger surface area of the sails equals the force of the daggerboard pushing against the water. A daggerboard fits into a trunk that runs through the hull of the rig. When the board is in the trunk it keeps the water out while in use due to how tightly wedged it is. It is held in place by a pin on the forward end or a shock cord. The daggerboard puts a counter force from the wind pushing on the sails. A sailboat can go in any direction, but not directly into the wind. During a storm, daggerboards can help reduce the tendency to tip over from waves. A catamaran in a storm would lift the daggerboard leeward and put the up wind half way in. If there is no wind and an outboard motor is being used, lifting the daggerboards will ensure the least drag.

History

A daggerboard is a removable keel that comes out vertically from its housing. Theses boards were made out of wood; the problem with wood is it floats. An alternate material that is great for daggerboards are metal (aluminum/steel) and fiberglass. The process in making a daggerboard rig is that it is very costly. If not well made the annoying sound of a rattle form the board trunk can destroy the interest of sailing. Dagger boards are fragile and will break if hit against a rock. The difference between daggerboards from centerboards and keels are it is removable. Centerboards are mechanically pivoted on a pin causing the board to swing into the hull of the boat. The advantage of it doing that is when you are sailing over shallow reef it won’t snap the board as if it were a fixed keel or daggerboard. Curved dagger boards started to appear thirty- forty years ago. The first prototype was made in 1985 by Ian Farrier. The benefits of vertical lift of the curved daggerboard on rigs showed on paper. When actually sailing curved daggerboards do not have a drastic change.

References

Hankinson, K. (1973). Rigging small sailboats. Bellflower, Calif.: Glen-L. Keel dagger board rudder. (n.d.). Retrieved March 22, 2015, from http://www.mecaflux.com/en/keel dagger board rudder.htm Firebird Catamaran. (n.d.). Retrieved March 22, 2015, from http://www.firebirdcat.com/technical_information.htm/technical_info_daggerboard.htm Rare dagger-board schooner discovered in deep water off Oswego, N.Y. Read more at http://www.toledoblade.comRare-dagger-board-schooner-discovered-in-deep-water-off-Oswego-N-Y. (2014, September 8). The Blade. Retrieved April 7, 2015, from http://www.toledoblade.com/local/2014/09/08/Rare-dagger-board-schooner-discovered-in-deep-water-off-Oswego-N-Y.html Daggerboards vs. Keels. (n.d.). Retrieved April 8, 2015, from http://www.multihullcompany.com/Article/Daggerboards_vs._Keels Multihull Keels and Daggerboards | Catamaran Dealer. (2009, March 12). Retrieved April 8, 2015, from http://www.aeroyacht.com/2009/03/12/multihull-keels-and-daggerboards/)