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Keel laid for the USS United States in drydock The keel plate of USS United States (CVA-58) being laid in a construction dry dock on 18 April 1948.jpg
Keel laid for the USS United States in drydock

The keel is the bottom-most longitudinal structural element on a watercraft. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. The laying of the keel is often the initial step in the construction of a ship. In the British and American shipbuilding traditions, this event marks the beginning date of a ship's construction. [1]



The word "keel" comes from Old English cēol, Old Norse kjóll, = "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 , under the spelling cyulae (he was referring to the three ships that the Saxons first arrived in). [2] [3]

Carina is the Latin word for "keel" and is the origin of the term careen (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, a suburb of Sydney, Australia, where careening was carried out in early colonial days.



Carvel-built hull construction (right) lines planks up edge to edge Clinker-carvel.svg
Carvel-built hull construction (right) lines planks up edge to edge

The use of a keel in sailing vessels goes back to antiquity. The wreck of an ancient Greek merchant ship known as the Kyrenia ship establishes the origin of the keel at least as far back as 315 BC. [4] [ page needed ] The Uluburun shipwreck (c. 1325 BC) had a rudimentary keel, but it may have been more of a center plank than a keel. [5]

Construction styles

Frame first

In carvel-built hulls, construction began with the laying of the keel, followed by the stern and stem. Frames were set up afterward, set at key points along the keel. Later, the keelson was attached to the keel, either bolted or with treenails. [6]

Plank first

Structural keels

A structural keel is the bottom-most structural member around which the hull of a ship is built. The keel runs along the centerline of the ship, from the bow to the stern. 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. [7]

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 scantlings, 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.[ citation needed ]

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. [8]

Sailing yacht with a fin keel MariahQuarterView.jpg
Sailing yacht with a fin keel
Lateral resistance effect of a sailing keel Capsizing effect of keel.svg
Lateral resistance effect of a sailing keel
Righting effect of a keel, where A is the center of buoyancy and G is the centre of gravity (hypothetical example). Segeln Gewichtsstabilitaet.svg
Righting effect of a keel, where A is the center of buoyancy and G is the centre of gravity (hypothetical example).

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 force of the wind. Related foils include centerboards and daggerboards, which do not have the secondary purpose of being a counterweight. As counterweight, a keel increasingly offsets the heeling moment with increasing angle of heel.

Moveable sailboat keels may pivot (a swing keel), [9] retract upwards (retracting keel), [10] 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. [11]

See also


  1. Man, Myth & Magic: The Illustrated Encyclopedia of Mythology, Religion and the Unknown. M. Cavendish. 1995. p. 2364. ISBN   9781854357311.
  2. "Gildas, The Ruin of Britain &c. (1899). pp. 4–252. The Ruin of Britain".
  3. G. W. Whittaker (1970). Collected Essays. Ayer Publishing. p. 44. ISBN   0-8369-1636-0.
  4. Katzev, Susan Womer; Swiny, Helena Wylde (2022). The Kyrenia Ship Final Excavation Report: Volume I - History of the Excavation, Amphoras, Pottery and Coins as Evidence for Dating. Oxbow Books. ISBN   9781785707520.
  5. Pulak, Cemal (1998). "The Uluburun Shipwreck: An Overview". The International Journal of Nautical Archaeology. 27 (3): 210. doi:10.1111/j.1095-9270.1998.tb00803.x.
  6. Adams, Jonathan R. (2013). A Maritime Archaeology of Ships: Innovation and Social Change in Late Medieval and Early Modern Europe: A Maritime Archaeology of Early Modern Europe. Oxford: Oxbow Books. p. 76. ISBN   978-1-78297-047-7. OCLC   862401040.
  7. Walton, Thomas (1901). Know Your Own Ship. London: Charles Griffin & Company. pp. 57–60. ISBN   9783861951643.
  8. Streiffert, Bo (September 1994). Modern Boat Maintenance: The Complete Fiberglass Boat Manual. Sheridan House, Inc. p. 173. ISBN   978-0-924486-71-5.
  9. Spurr, Daniel (2004-07-02). Your First Sailboat: How to Find and Sail the Right Boat for You. McGraw Hill Professional. p. 10. ISBN   9780071778770.
  10. Kent, Duncan (2011-02-04). The Insider's Guide to Choosing & Buying a Yacht: Expert Advice to Help You Choose the Perfect Yacht. Fernhurst Books Limited. ISBN   978-1-119-99918-8.
  11. Slooff, J. W. (2015-04-25). The Aero- and Hydromechanics of Keel Yachts. Springer. p. 190. ISBN   9783319132754.


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