A skeg (or skag) is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line. The term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard. In more recent years, the name has been used for a fin on a surfboard which improves directional stability and to a moveable fin on a kayak which adjusts the boat's centre of lateral resistance. The term is also often used for the fin on water skis in the U.S.A.
The word originates in the Scandinavian word for beard; in Old Norse, skegg. In Icelandic the word remains skegg, in modern Norwegian Bokmål and Nynorsk, it appears as skjegg, in Swedish, it is skägg and in Danish, skæg. The Norwegian pronunciation of the letter combination skj is as in the English sh. The word is related to the English shaggy. It also appears in the English place name Skegness - 'beard point', from the way in which a series of tombolos forms, towards the nearby Gibraltar Point. Here, the English pronunciation reflects a probable Danish origin, which pronounces the sk letter combination as an English speaker would expect. However, 'Skegness' is pronounced with an un-Danish hard 'g'.
In boats and ships
Where a vessel's rudder is mounted on the centre-line, it is usual to hang it on gudgeons and pintles, the latter being upright pins and the former, rings to fit round them. Together, they form a hinge. This naturally leaves a small gap between the sternpost and the rudder, into which stray items like kelp and rope can catch, causing drag and threatening the security of the vessel's steering. In ships such as Mary Rose, the skeg is a very small feature; a tapered extension of the keel below the leading edge of the rudder. This somewhat beard-like sternward extension of the keel is the basic skeg. Subsequently, the lowest pintle was commonly mounted below the rudder on a metal extension of the keel. This helped further stabilize and protect the rudder and the name, skeg was transferred to it. It used still to be relatively small until screw propellers were introduced, when it had to reach below the screw and became a proportionately larger feature protecting both screw and rudder from damage.
On wooden vessels, the skeg may be protected from worm damage by the addition of a bug shoe.
In more modern installations, with more than one screw, a fitting supports each propeller shaft just ahead of its screw. This is usually called a shaft bracket but the part of it which extends below the shaft bearing to protect the lower part of the propeller is also a skeg. Similarly, the protective projection of the drive casing, below the rotational axis of the propeller of an outboard motor is another form of the skeg.
Where a yacht is designed with a fin keel, it will normally, also have a skeg-mounted rudder. This link shows the profile of such a boat. This type of skeg is pictured at the bottom of the same linked page.
In surfing, windsurfing, and kitesurfing the fin, sometimes known as a skeg, is located towards the rear of the surfboard. A surf board fin improves the board's directional stability and enables directional control by banking, known as foot-steering, which involves varying the surfer's side to side weight distribution.
The fin was introduced in 1936 by Woody "Spider" Brown", later inventor of the modern catamaran, when he built America's first modern surfboard (i.e., capable of being surfed standing up) using principles learned during his decade of aeronautical experience. Despite this, it is usually attributed to Tom Blake. Blake claimed to have removed a skeg from a water ski then screwed it onto the bottom of his solid wood board (not capable of being surfed standing up). Brown, whose later invention of the catamaran was subsequently patented by Hobie Alter, similarly refused to contest this claim.
Small single aluminum fins first evolved into single larger wooden, then fiberglass and carbon versions. In early surf boards the beaks from Duck-Foxes were used. In time hydrodynamic improvements took place, pioneered by George Downey who also created the first removable skeg, a teak wood skeg in a teak wood box which was supposed to hold in place due to the swelling of woods in water. In modern surfing board design, the conventional set up is 3 fins, with single fins being a minority. Most windsurfers are single fin, with some twin fin designs being employed. Directional kitesurfing boards are usually 3 fin, with 5 fin designs being used for improved upwind performance.
A skeg is employed in the type of kayak used on more open water such as the sea. Its purpose and use are rather different from those of the surfing skeg. In the kayak, the amount of exposure of the skeg to the water, and also its effect on the position of the boat's centre of lateral resistance (CLR), is freely adjustable by the crew. The adjustment varies the degree to which the wind affects the boat - that is, the amount of lateral movement the wind can cause by impacting the upper parts of the boat and the crew. In more conventional calculations, this would be the centre of effort of the sail area (CE). In still water, where the wind is pushing the boat sideways, a contrary force (lateral resistance) develops, resisting that movement. If the central points of the application of those two forces coincide, the boat moves steadily sideways. Otherwise, it rotates in the horizontal plane, until they are in line. By varying the CLR, it is possible to better control the boat's attitude towards the wind. Irregular flowing movement of the water complicates the issue, however. This link explains the subtleties of the kayak skeg.
In Hull, a city on the eastern coast of Yorkshire, UK, 'skeg' is often used to mean 'look' - usually as a noun, but sometimes as a verb. Hence, "Gis a skeg," meaning, "Could I please look?"; and (as a verb) "Skeg out the state a that daft silly get," meaning "Have you noticed the eccentric nature of that person over there?"
Skeg is an abbreviation for Skegness
- Davison, Phil (2008.05.03) Record-breaking aviator who became a legendary surfer The Financial Times (obituary)
In the eighties the term skeg was used to refer to a surfer. This was commonly used in Australia when there were clashes between skegs (surfers) and Bogans.
- This site shows the fins on a surf kayak, a boat combining some of the features of a kayak with some of a surf board.
- This site offers an easy do-it-yourself repair for broken skegs.