Keel
In boat construction,
keel can refer to two different but overlapping parts; a structural element, or a hydrodynamic element.
A structural keel is a large beam around which the
hull of a
ship is built. The keel runs in the middle of the ship, from the
bow to the
stern, and serves as the
foundation or
spine of the structure, providing the major source of structural strength of the hull. The keel is generally 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, is often a momentous event in a ship's construction--so much so that the event is often marked with a ceremony, and the term
lay the keel has entered the language as a phrase meaning the beginning of any significant undertaking.
A hydrodynamic
keel is a
foils on the bottom of the hull that is used to give the ship greater directional control and
stability. In traditional boatbuilding, this is provided by the structural keel, which projects from the bottom of the hull along most or all of its length. In non
sailing hulls, the keel helps the hull to move forward, rather than slipping to the side.
In
sailboats, keels use the forward motion of the boat to generate
lift to counter the lateral force from the
sails. To counter the large lateral force generated by the sails, sailboats have much larger keels than non sailing hulls. Keels are different from
centerboards and other types of foils in that keels are made of heavy materials to provide
ballast to stabilize the boat. Keels may be
fixed, or non-moveable, or they may retract to allow sailing in shallower waters. Retracting keels may pivot (a
swing keel) or slide upwards to retract, and are usually retracted with a
winch due to the ballast. Since the keel provides far more stability when lowered than when retracted (due to the greater
moment arm involved) the amount of sail carried is generally reduced when sailing with the keel is retracted.
There are several types of fixed keels including: full keels, fin keels,
winged keels,
bulb keels, and
canting keels, among other designs.
Carina is the
Latin word for keel and is the origin of the term
careen (to clean a keel and the hull in general). An example of this use is
Careening Cove, a suburb of
Sydney, Australia, where careening was carried out in early colonial days.
*
Leeboard*
Bilgeboard*
Daggerboard*
Bruce foil*
Bulb keel,
winged keel and
canting keel provide even greater control and stability for a yacht
*
Keelhauling a type of sailor's punishment
*
Kelson
