200px, Flat Keel bulb A bulb keel is a

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

, usually made with a high aspect ratio

foil Foil may refer to: Materials * Foil (metal), a quite thin sheet of metal, usually manufactured with a rolling mill machine * Metal leaf, a very thin sheet of decorative metal * Aluminium foil, a type of wrapping for food * Tin foil, metal foil ...

, that contains a

ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...

-filled bulb at the bottom, usually teardrop shaped. The purpose of the bulb keel is to place the ballast as low as possible, therefore gaining the maximum possible amount of

lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or '' fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is d ...

age and thus the most righting

moment Moment or Moments may refer to: * Present time Music * The Moments, American R&B vocal group Albums * ''Moment'' (Dark Tranquillity album), 2020 * ''Moment'' (Speed album), 1998 * ''Moments'' (Darude album) * ''Moments'' (Christine Guldbrand ...

. An example of a class of boats that use a bulb keel is the

International 110 The International 110 is an American sailboat that was designed by C. Raymond Hunt as a one-design Sailing (sport), racer and first built in 1939.Sherwood, Richard M.: ''A Field Guide to Sailboats of North America, Second Edition'', pages 122-1 ...

racing class, which uses a 300 lb (136 kg) cast iron bulb keel on a boat whose minimum racing weight is 910 lb (414 kg). Since bulb keels work best on long, thin keels or

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, co ...

s, they are generally not used on

sailboat A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture. Types Although sailboat terminology ...

s intended for shallow waters, but are most often found on offshore racing craft. Daggerboards built like bulb keels are often referred to as "lifting keels", and they can be retracted into the boat to reduce the draft, and to allow the boat to be loaded onto a trailer. Lifting keels are also more likely to be found on craft built for speed, as a

winch A winch is a mechanical device that is used to pull in (wind up) or let out (wind out) or otherwise adjust the tension of a rope or wire rope (also called "cable" or "wire cable"). In its simplest form, it consists of a spool (or drum) attach ...

or a set of

pulley A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...

s is required to provide purchase to lift the heavy keel. Some boats with lifting keels go so far as to allow the keel to be canted side to side, allowing the bulb to be placed to

windward Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

to reduce heel in high winds; this type of keel is called a

canting keel A canting keel is a form of sailing ballast, suspended from a rigid canting strut beneath the boat, which can be swung to windward of a boat under sail, in order to counteract the heeling force of the sail. The canting keel must be able to pivot ...

, and is used in the newest

Volvo Ocean Race The Ocean Race is a yacht race around the world, held every three or four years since 1973. Originally named the Whitbread Round the World Race after its initiating sponsor, British brewing company Whitbread, in 2001 it became the Volvo Ocean Ra ...

Volvo Open 70 The Volvo Open 70 (sometimes referred to as a Volvo Ocean 70) is the former class of racing yachts designed for the Volvo Ocean Race. It was first used in the 2005–06 race (replacing the Volvo Ocean 60 yachts which were first used in 1993). A ...

class

yacht A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, though the term generally applies to vessels with a cabin intended for overnight use. To be termed a , as opposed to a , such a pleasu ...

s. It is also possible to shape the bulb into a horizontal foil, called a winged keel. When the bulb protrudes past the leading edge of the keel, it is called a "T-bulb". It offers better performance (like required for racing), but is prone to hook into

flotsam In maritime law, flotsam'','' jetsam'','' lagan'','' and derelict are specific kinds of shipwreck. The words have specific nautical meanings, with legal consequences in the law of admiralty and marine salvage. A shipwreck is defined as the rema ...

(like kelp or discarded fishing nets).

References

{{DEFAULTSORT:Bulb Keel Sailboat components Sailing ship components Nautical terminology

See also

References