Point of sail

A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface.

The principal points of sail roughly correspond to 45° segments of a circle, starting with 0° directly into the wind. For many sailing craft 45° on either side of the wind is a "no-go" zone, where a sail is unable to mobilize power from the wind. Sailing on a course as close to the wind as possible—approximately 45°—is termed "close-hauled". At 90° off the wind, a craft is on a "beam reach". At 135° off the wind, a craft is on a "broad reach". At 180° off the wind (sailing in the same direction as the wind), a craft is "running downwind".

In points of sail that range from close-hauled to a broad reach, sails act substantially like a wing, with lift predominantly propelling the craft. In points of sail from a broad reach to down wind, sails act substantially like a parachute, with drag predominantly propelling the craft. For craft with little forward resistance ice boats and land yachts, this transition occurs further off the wind than for sailboats and sailing ships. In the no-go zone sails are unable to generate motive power from the wind.

Wind direction for points of sail always refers to the true wind—the wind felt by a stationary observer. The apparent wind—the wind felt by an observer on a moving sailing craft—determines the motive power for sailing craft.

Sailing craft, such as sailboats and ice boats, cannot sail directly into the wind, nor on a course that is too close to the direction from which the wind is blowing. The range of directions into which a sailing craft cannot sail is called the "no-go" zone. In the no-go zone the craft's sails cease producing enough drive to maintain way or forward momentum. Therefore, the sailing craft slows down towards a stop and steering becomes progressively less effective at controlling the direction of travel. The span of the no-go zone varies among sailing craft, depending on the design of the sailing craft, its rig, and its sails, as well as on the wind strength and, for boats, the sea state. Depending on the sailing craft and the conditions, the span of the no-go zone may be from 30 to 50 degrees either side of the wind, a 60- to 100-degree area centered on the wind direction.

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