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 British and American shipbuilding traditions the construction is dated from this event.

Etymology

The word "keel" comes from

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...

, Old Norse , = " ship" or "keel". It has the distinction of being regarded by some scholars as the first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work ''

De Excidio et Conquestu Britanniae ''De Excidio et Conquestu Britanniae'' ( la, On the Ruin and Conquest of Britain, sometimes just ''On the Ruin of Britain'') is a work written in Latin by the 6th-century AD British cleric St Gildas. It is a sermon in three parts condemning ...

'', under the spelling ''cyulae'' (he was referring to the three ships that the Saxons first arrived in). is the Latin word for "keel" and is the origin of the term

careen Careening (also known as "heaving down") is a method of gaining access to the hull of a sailing vessel without the use of a dry dock. It is used for cleaning or repairing the hull. Before ship's hulls were protected from biofouling, marine growth ...

(to clean a keel and the hull in general, often by rolling the ship on its side). An example of this use is

Careening Cove Careening Cove, is a bay on the northern side of Sydney Harbour, near Milsons Point. The cove lies in the traditional lands of the Cammeraygal people, who called it Wia Wia. It was later named for its use in the early days of European settleme ...

, a suburb of

Sydney, Australia Sydney ( ) is the capital city of the States and territories of Australia, state of New South Wales, and the most populous city in both Australia and List of cities in Oceania by population, Oceania. Located on Australia's east coast, the metro ...

, where careening was carried out in early colonial days.

Structural keels

A structural keel is the bottom-most structural member around which the

hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a ship * Submarine hull Mathematics * Affine hull, in affi ...

of a ship is built. The keel runs along the centerline of the ship, from the bow to the

stern The stern is the back or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite the bow, the foremost part of a ship. Ori ...

. The keel is often the first part of a ship's hull to be constructed, and laying the keel, or placing the keel in the cradle in which the ship will be built may mark the start time of its construction. Large, modern ships are now often built in a series of pre-fabricated, complete hull sections rather than being built around a single keel, so the shipbuilding process commences with the cutting of the first sheet of steel. The most common type of keel is the "flat plate keel", and this is fitted in the majority of ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers, tugs, and smaller ferries. Where grounding is possible, this type of keel is suitable with its massive

scantling Scantling is a measurement of prescribed size, dimensions, or cross sectional areas. Shipping In shipbuilding, the scantling refers to the collective dimensions of the framing (apart from the keel) to which planks or plates are attached to form th ...

s, but there is always a problem of the increased draft with no additional cargo capacity. If a double bottom is fitted, the keel is almost inevitably of the flat plate type, bar keels often being associated with open floors, where the plate keel may also be fitted.

Hydrodynamic keels

Hydrodynamic keels have the primary purpose of interacting with the water and are typical of certain sailboats. Fixed hydrodynamic keels have the structural strength to support the weight of the boat. Segeln Gewichtsstabilitaet

Sailboat keels

In sailboats, keels serve two purposes: 1) as an underwater foil to minimize the lateral motion of the vessel under sail ( leeway) and 2) as a counterweight to the lateral force of the wind on the sail(s) that causes rolling to the side ( heeling). As an underwater foil, a keel uses the forward motion of the boat to generate lift to counteract the

leeward 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 ...

force of the wind. Related foils include centerboards and

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, cou ...

s, which do not have the secondary purpose of being a counterweight. As counterweight, a keel increasingly offsets the heeling

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with increasing angle of heel. Moveable sailboat keels may pivot (a swing keel), retract upwards (retracting keel), or swing sideways in the water (canting keels) to move the ballasting effect to one side and allow the boat to sail in a more upright position.

Notes

Bibliography

* Rousmaniere, John, ''The Annapolis Book of Seamanship'', Simon & Schuster, 1999 * ''Chapman Book of Piloting'' (various contributors), Hearst Corporation, 1999 * Herreshoff, Halsey (consulting editor), ''The Sailor’s Handbook'', Little Brown and Company * Seidman, David, ''The Complete Sailor'', International Marine, 1995 * Jobson, Gary, ''Sailing Fundamentals'', Simon & Schuster, 1987 {{Authority control Nautical terminology Naval architecture Sailing rigs and rigging Sailing vessel components Shipbuilding Sailboat components

Etymology

Structural keels

Hydrodynamic keels

Sailboat keels

See also

Notes

Bibliography