A modern windsurfing
sail is made of monofilm
. Sensitive parts are reinforced with kevlar
Currently, two desingns of a sail are predominant: camber induced and RAF (Rotating Asymmetric Foil). Cambered sails are more stable and powerful, but are more difficult to handle during manoeuvres. The current trend is that only the large race sails have camber inducers. The rigidity of the sail is also determined by a number of battens.
The leading edge of a sail is called the luff. The mast is in the luff tube. The rear edge is called the leech. The front bottom corner of the sail, where the mast foot protrudes, is called the the tack, and the rear corner, to which the boom is atached, is called the clew. The bottom edge, between the clew ant the tack, is called the foot.
A windsurfing sail is tensioned at two points: at the tack (by downhaul), and at the clew (by outhaul). There is a set of pulleys for downhauling at the tack and there's a grommet at the clew. Most shape is given to the sail by a very strong downhaul, bending the mast in the luff tube. The outhaul tension is relatively weak, mostly just to keep the sail from flapping.
The sail is tuned by adjusting the downhaul and the outhaul. Generally, the sail has to be trimmed more for stronger winds. More downhaul tension loosens the upper part of the leech, "spilling" the wind at the gusts and shifting the center of effort of the sail down. In contrary, releasing the downhaul tension shifts the CoE up. More outhaul makes the sail flatter, easier to control, but less powerful, and less outhaul brings more camber, more low-end power, shifts the CoE to the front, and limits the speed by increasing the aerodynamic resistance.
There are different kinds of sails for different kinds of windsurfing: wave, freestyle, freeride, race.
The size of the sail is measured in square metres and it can be anything from 3 m2 to 6.5 m2 for wave sails and from 6 m2 to 12 m2 for racing sails, with ranges for freestyle and freeride sails spanning somewhere between these extremes.