Sail twist is a phenomenon in

sailing Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' (sailing ship, sailboat, raft, Windsurfing, windsurfer, or Kitesurfing, kitesurfer), on ''ice'' (iceboat) or on ''land'' (Land sa ...

where the head of the

sail A sail is a tensile structure, which is made from fabric or other membrane materials, that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may b ...

is at a different angle of incidence from the foot of the sail in order to change the

lift distribution When a fluid flows around an object, the fluid exerts a force on the object. Lift is the Euclidean_vector#Decomposition_or_resolution, component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag (phy ...

with height. Twist is measured by comparing the angle of a straight line between the leading edge (luff) and trailing edge (leech) with that of the boom. Some twist is desirable, but too much can induce weather helm or ruin the slot between the

mainsail A mainsail is a sail rigged on the main mast (sailing), mast of a sailing vessel. * On a square rigged vessel, it is the lowest and largest sail on the main mast. * On a fore-and-aft rigged vessel, it is the sail rigged aft of the main mast. T ...

and jib. Three sail shape controls which control the leech tension, and therefore sail twist, are the mainsheet, the boom vang and the traveler. The mainsheet pulls the boom (and therefore the foot of the sail) primarily inwards at lower points of sail and downwards at higher points of sail. Manipulation of the traveler can counteract this because it always pulls the boom laterally. The vang on the other hand does the opposite, it always changes the height of the boom. Computer cut sails can produce the amount of twist specified by the sailmaker, and in different conditions, different amounts of twist may be desirable. Less twist is generally desirable in light air conditions and slackening the luff tension will tighten the leech of the sail. This moves the center of effort on the sail toward the trailing edge and reduces twist thus making the sail more powerful but vulnerable to stalling.

References

{{reflist Sailing rigs and rigging

See also

References