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.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 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). 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.
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.
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 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, or a "a length of hardened material, such as ironbark, 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.
In surfing, windsurfing, 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 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 and carbon fiber. In time, hydrodynamic improvements took place, pioneered by George Downing Archived 2015-09-28 at the Wayback Machine 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.
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 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.
Skegs have been used to improve the directional stability of seaplanes. They have been installed on floatsand hulls
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.
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.
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 nalu in the Hawaiian language, and were usually made of wood from local trees, such as koa. They were often over 460 cm (15 ft) in length and extremely heavy. Major advances over the years include the addition of one or more fins (skegs) on the bottom rear of the board to improve directional stability, and numerous improvements in materials and shape.
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. On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull (watercraft) or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail, or after end. Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tiller—essentially, a stick or pole acting as a lever arm—may be attached to the top of the rudder to allow it to be turned by a helmsman. In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.
A runabout is any small motorboat holding between four and eight people, well suited to moving about on the water. Characteristically between 20' to 35' in length, runabouts are used for pleasure activities like boating, fishing, and water skiing, as a ship's tender for larger vessels, or in racing. Some common runabout types are bow rider, center console, cuddy boat and walkaround. The world's largest runabout, Pardon Me, is 48 feet long and owned by the Antique Boat Museum in Clayton, New York.
A sea kayak or touring kayak is a kayak developed for the sport of paddling on open waters of lakes, bays, and the ocean. Sea kayaks are seaworthy small boats with a covered deck and the ability to incorporate a spray deck. They trade off the manoeuvrability of whitewater kayaks for higher cruising speed, cargo capacity, ease of straight-line paddling, and comfort for long journeys.
Boat building is the design and construction of boats and their systems. This includes at a minimum a hull, with propulsion, mechanical, navigation, safety and other systems as a craft requires.
The Jersey Skiff is a beach launched boat first appearing around the end of the 19th century. They were first used as fishing boats, to be launched through the surf, sailed to the fishing grounds and then retrieved through the surf.
A Z-drive is a type of marine propulsion unit. Specifically, it is an azimuth thruster. The pod can rotate 360 degrees allowing for rapid changes in thrust direction and thus vessel direction. This eliminates the need for a conventional rudder.
A surfski is a type of kayak in the kayaking "family" of paddling craft. It is generally the longest of all kayaks and is a performance oriented kayak designed for speed on open water, most commonly the ocean, although it is well suited to all bodies of water and recreational paddling.
Skurfing is a towed water sport similar to waterskiing, in that an individual is pulled behind a boat on a tow rope. However, instead of water skis, the sport uses a skurfboard which is a floating platform the user balances on, similar to a surfboard, but typically much shorter, with two foot-straps that prevent falling off the board and three fins positioned on the bottom that make it easier to maneuver when the board is being towed. The word itself is a portmanteau of skiing and surfing. Skurfing is often considered the precursor to wakeboarding.
A sailing yacht, is a leisure craft that uses sails as its primary means of propulsion. A yacht may be a sail or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies here to sailing vessels that have a cabin with amenities that accommodate overnight use. To be termed a "yacht", as opposed to a "boat", such a vessel is likely to be at least 33 feet (10 m) in length and have been judged to have good aesthetic qualities. Sailboats that do not accommodate overnight use or are smaller than 30 feet (9.1 m) are not universally called yachts. Sailing yachts in excess of 130 feet (40 m) are generally considered to be superyachts.
A surfboard fin or skeg is a hydrofoil mounted at the tail of a surfboard or similar board to improve directional stability and control through foot-steering. Fins can provide lateral lift opposed to the water and stabilize the board's trajectory, allowing the surfer to control direction by varying their side-to-side weight distribution. The introduction of fins in the 1930s revolutionized surfing and board design. Surfboard fins may be arrayed in different numbers and configurations, and many different shapes, sizes, and materials are and have been made and used.
The center of lateral resistance is the center of pressure of the hydrodynamic forces on the hull of a boat. The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure location produce equivalent force and moment on the body as the original pressure field. Pressure fields occur in both static and dynamic fluid mechanics. Specification of the center of pressure, the reference point from which the center of pressure is referenced, and the associated force vector allows the moment generated about any point to be computed by a translation from the reference point to the desired new point.
The Endeavour 40 is an American sailboat that was designed by Robert K. Johnson as a cruiser and first built in 1981.
The Columbia 7.6 is an American/Canadian trailerable sailboat that was designed by Australian Alan Payne as a cruiser and first built in 1976.
The ETAP 21i is a Belgian trailerable sailboat that was designed by Mortain & Mavrikios as a cruiser and first built in 1997.
The Seafarer 22 is an American trailerable sailboat that was designed by McCurdy & Rhodes as a cruiser and first built in 1976.
The Seafarer 23 is an American trailerable sailboat that was designed by McCurdy & Rhodes as a cruiser and first built in 1976.
The Signet 20 is a British trailerable sailboat that was designed by Ray Kaufmann as day sailer and pocket cruiser and first built in 1960.