A skeg (or skegg or skag) is a sternward extension of the
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 B ...
of boats and ships which have a
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw a ...
mounted on the centre line. The term also applies to the lowest point on an
outboard motor or the outdrive of an
inboard/outboard
A sterndrive or inboard/outboard drive (I/O) is a form of marine propulsion which combines inboard power with outboard drive. The engine sits just forward of the transom while the drive unit (outdrive or drive leg) lies outside the hull.
Operat ...
.
["A small fin fitted aft of the keel to protect the rudder and propeller, and improve steering and tracking." ]["Skeg, or Skegg. A projecting stump formerly left on the keel, abaft the stern-post. The after-end of the keel. The composition piece supporting the heel of an equipoise rudder." at ]Internet Archive
The Internet Archive is an American digital library with the stated mission of "universal access to all knowledge". It provides free public access to collections of digitized materials, including websites, software applications/games, music ...
In more recent years, the name has been used for a
fin on a
surfboard
A surfboard is a narrow plank used in surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean wave. They were invented in ancient Hawaii, where they were known as ''papa he' ...
which improves
directional stability and to a movable fin on a
kayak
A kayak is a small, narrow watercraft which is typically propelled by means of a double-bladed paddle. The word kayak originates from the Greenlandic word '' qajaq'' ().
The traditional kayak has a covered deck and one or more cockpits, each ...
which adjusts the boat's
centre of lateral resistance (it moves the center of resistance relative to the center of effort).
The term is also often used for the fin on water skis in the U.S. It has been used for the vertical fin on seaplane hulls and floats. The wear-bar on the bottom of snowmobile ski may also be called a skeg.
Etymology
The word originates in the
Scandinavian word for
beard
A beard is the hair that grows on the jaw, chin, upper lip, lower lip, cheeks, and neck of humans and some non-human animals. In humans, usually pubescent or adult males are able to grow beards.
Throughout the course of history, societal a ...
; in Old Norse, ''skegg''. In
Icelandic the word remains ''skegg'', in modern
Norwegian Bokmål
Bokmål () (, ; ) is an official written standard for the Norwegian language, alongside Nynorsk. Bokmål is the preferred written standard of Norwegian for 85% to 90% of the population in Norway. Unlike, for instance, the Italian language, there ...
and
Nynorsk
Nynorsk () () is one of the two written standards of the Norwegian language, the other being Bokmål. From 12 May 1885, it became the state-sanctioned version of Ivar Aasen's standard Norwegian language ( no, Landsmål) parallel to the Dano- ...
, it appears as ''skjegg'', in
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
, 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.
In boats and ships
Where a vessel's
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw a ...
is mounted on the centre-line, it is usual to hang it on
gudgeon
A gudgeon is a socket-like, cylindrical (i.e., '' female'') fitting attached to one component to enable a pivoting or hinging connection to a second component. The second component carries a pintle fitting, the male counterpart to the gudgeon, ...
s 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
A sternpost is the upright structural member or post at the stern of a (generally wooden) ship or a boat, to which are attached the transoms and the rearmost left corner part of the stern.
The sternpost may either be completely vertical or m ...
and the rudder, into which stray items like
kelp
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms.
Kelp grows in "under ...
and
rope
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similarly ...
can catch, causing drag and threatening the security of the vessel's steering. In ships such as ''
Mary Rose
The ''Mary Rose'' (launched 1511) is a carrack-type warship of the English Tudor navy of King Henry VIII. She served for 33 years in several wars against France, Scotland, and Brittany. After being substantially rebuilt in 1536, she saw her ...
'', the skeg is a very small feature; a tapered extension of the
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 B ...
below the leading edge of the rudder. This somewhat beard-like
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 ...
ward 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 to be relatively small until screw
propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
s 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, or a "a length of hardened material, such as
ironbark
Ironbark is a common name of a number of species in three taxonomic groups within the genus ''Eucalyptus'' that have dark, deeply furrowed bark.
Instead of being shed annually as in many of the other species of ''Eucalyptus'', the dead bark accum ...
, placed on the sternward keel extension (skeg) to protect from shipworm damage."
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.
Surfing
In
surfing,
windsurfing
Windsurfing is a wind propelled water sport that is a combination of sailing and surfing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the aerospace and surf culture of California. Windsurfing g ...
, and
kitesurfing, skegs, usually known as "
fins", are attached toward the tail of the board to improve directional stability and control through foot-steering. Fins allow the rider to control the board's direction by varying their side-to-side weight distribution.
Fixed fins were introduced to
surfboards
A surfboard is a narrow plank used in surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean wave. They were invented in ancient Hawaii, where they were known as ''papa he'e ...
by surfing pioneer
Tom Blake in 1935. Around 1936,
Woody Brown independently added a fixed fin to his second surfboard design, which further popularized the feature. The stability and control it allowed revolutionized the sport.
Small single aluminum fins first evolved into larger wooden versions, then ones made from
fiberglass
Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cl ...
and
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
. In time, hydrodynamic improvements took place, pioneered b
George Downing who also created the first removable skeg, which was a teak wood skeg in a teak wood box which was supposed to be held in place by the swelling of the wood in water. In modern surfing board design, the conventional set-up is to have three fins, with single fins being a minority. While most windsurfing boards are single-fin, wave boards now feature some twin-fin, tri-fin and quad-fin designs. Directional kitesurfing boards are usually three-fin, with five-fin designs being used for improved upwind performance.
Kayaks
A skeg is employed in the type of
kayak
A kayak is a small, narrow watercraft which is typically propelled by means of a double-bladed paddle. The word kayak originates from the Greenlandic word '' qajaq'' ().
The traditional kayak has a covered deck and one or more cockpits, each ...
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 and waves. Irregular flowing movement of the water complicates the issue, however.
[This link]
explains the subtleties of the kayak skeg. They may be made of wood, fiberglass or aluminum. Some are deployed using internal cables, but others use external ropes and bungee cord.
Typically, these are retractable, and they are not a rudder. If properly configured (e.g., use of street sign aluminum in a narrow box that extends through the hull) they will not flex, and will greatly decrease and counter pitch, roll and yaw, like a centerboard on a sailboat, when the craft is moving. In that sense, the skeg acts as a lifting foil.
Aircraft
Skegs have been used to improve the directional stability of seaplanes. They have been installed on floats and hulls[https://calhoun.nps.edu/handle/10945/24676, p.6]
Snowmobiles
The skis on a snowmobile have a metal wear-bar on the bottom of them. Many sledders call these "skegs". These skegs help the skis to steer on hard surfaces. These often have carbide embedded in them to reduce wear when driven on non-snow surfaces.
See also
* Glossary of nautical terms (A-L)
* Glossary of nautical terms (M-Z)
Notes
References
Further reading
*
{{Sailing ship elements
Nautical terminology
Naval architecture
Sailboat components
Sailing rigs and rigging
Sailing ship components
Shipbuilding
Surfing equipment
Watercraft components