Skeg
A skeg (or skegg or skag) is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line.[1] The term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard.[A][B] In more recent years, the name has been used for a fin on a surfboard which improves directional stability and to a movable fin on a kayak which adjusts the boat's centre of lateral resistance (it moves the center of resistance relative to the center of effort).[2] 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; 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.
In boats and ships
Where a vessel's
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, placed on the sternward keel extension (skeg) to protect from shipworm damage."[3]
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
Fixed fins were introduced to
Small single aluminum fins first evolved into larger wooden versions, then ones made from
Kayaks
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.[2][7][8] 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.[2] 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..
Aircraft
Skegs have been used to improve the directional stability of seaplanes. They have been installed on floats[10] and hulls.[11]
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
Notes
- ^ "A small fin fitted aft of the keel to protect the rudder and propeller, and improve steering and tracking." MacKenzie, Mike (2005–2012). "Skeg". Seatalk, the Dictionary of English Nautical Language. Retrieved February 14, 2014.
- ^ "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." A naval encyclopædia: comprising a dictionary of nautical words and phrases; biographical notices, and records of naval officers; special articles of naval art and science. PHILADELPHIA: LR HAMERSLY & CO. 1881. Retrieved February 14, 2014. at Internet Archive
References
- ^ Smyth, W. H.; Belcher, E. (1867). Skegg. London: Blackie and Son. p. 638.
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ignored (help) - ^ a b c Watson, Tom (February 12, 2014). "Rudders & Skegs: Maneuvering Aids". paddling.net. Archived from the original on February 23, 2014. Retrieved February 12, 2014.
- ^ "AFSC Historical Corner: Scoter, the Agency's Bristol Bay Boat". NOAA. Retrieved 6 April 2018.
- ISBN 978-0-7627-4621-7. Retrieved April 8, 2013.
- ISBN 1610606868. Retrieved April 10, 2013.
- ^ "George Downing". Encyclopedia of Surfing. Archived 2015-09-28 at the Wayback Machine
- ^ a b "Fixing up your boat: Installing a retractable skeg". Chesapeake Lightcraft. Retrieved February 15, 2014.
- ^ a b "How does a kayak skeg work". Atlantic Kayak Tours. 2013. Archived from the original on February 23, 2014. Retrieved February 15, 2014.
- ^ "Rudders vs Skegs". Sea Kayaker Magazine. May 28, 2008. Retrieved February 15, 2014.
- ^ "1944 -1945". Aircraft Reports - Aircraft Manuals - Aircraft Helicopter Engines Propellers Blueprints Publications. 2024-04-01. Retrieved 2024-04-01., Figure 38 Float construction
- ^ Libbey, Lester Blaine (1950). "The effectiveness of water rudders on flying boats". Stevens Institute of Technology. Retrieved 2024-04-01., p.6
Further reading
- ISBN 978-0393339185