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.

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.

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.

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.

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.

[6] 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.

[7] Around 1936, Woody Brown independently added a fixed fin to his second surfboard design, which further popularized the feature.

[8] Small single aluminum fins first evolved into larger wooden versions, then ones made from fiberglass and carbon fiber.

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.

[10][11][12] 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.