Windsurfing - Sails

Sails

A windsurfing sail is made of monofilm (clear polyester film), dacron (woven polyester) and mylar. Sensitive parts are reinforced with kevlar mesh.

Two designs of a sail are predominant: camber induced and rotational. Cambered sails have 1-5 camber inducers, plastic devices at the ends of battens which cup against the mast. They help to hold a rigid aerofoil shape in the sail, better for speed and stability, but at the cost of maneuverability and generally how light and easy to use the sail feels. The trend is that racier sails have camber inducers while wave sails and most recreational sails do not. The rigidity of the sail is also determined by a number of battens.

Beginners' sails often do not have battens, so they are lighter and easier to use in light winds. However, as the sailor improves, a battened sail will provide greater stability in stronger winds.

Rotational sails have battens which protrude beyond the back aspect of the mast. They have to flip to the other side of the mast when tacking or jibing, hence the rotation in the name. Rotational sails have aerofoil shape on the leeward side only when filled with wind. They can be absolutely flat and depowered when sheeted out.

In comparison with cambered sails, rotational designs offer less power and stability when sailing straight, but are easier to handle when maneuvering. Also, rotational sails are much easier to rig.

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 tack, and the rear corner, to which the boom is attached, is called the clew. The bottom edge, between the clew and 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 to provide leverage for controlling the sail's angle of attack.

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 (strictly, the center of pressure) of the sail down. Releasing the downhaul tension shifts the center of effort up. More outhaul lowers the camber/draft, making the sail flatter and easier to control, but less powerful, and less outhaul brings more overall depth to the sail, more low-end power, shifts the center of effort upward and to the front, and may limit speed by increasing aerodynamic resistance.

The disciplines of windsurfing (wave, freestyle, freeride) require different sails. Wave sails are reinforced to survive the surf, and are flat when depowered to allow riding the waves like surfers do. Freestyle sails are also flat when depowered, and have high low-end power to allow quick acceleration. Freeride sails are all-rounders that are comfortable to use and are meant for recreational windsurfing. Racing sails provide speed at the expense of qualities like comfort or maneuverability.

The size of the sail is measured in square meters and can be from 3 m2 to 5.5 m2 for wave sails and from 6 m2 to 15 m2 for racing sails, with ranges for freestyle and freeride sails spanning somewhere between these extremes. Learning sails for children can be as small as 0.7 m2 and racing sails being up to 15 m2 large.