A sailboat harnesses wind forces differently depending on the direction it travels with respect to the wind. This direction is formally known as the point of sail or tack. Each point of sail has an optimal sail configuration that harnesses lift and drag forces most efficiently to propel the boat forward. We’ve alluded to these earlier, but the complete array of points of sail, and their formal names are shown in the illustration below.

Notice that there is an area directly into the wind that the boat cannot travel, known as the no go zone. If a sail points too closely to the wind, the air will tend to flow equally on either side of the sail and it will lose its airfoil shape and begin to flap loosely in the wind, much like a flag. In this condition, the sail is luffing, and does not capture significant aerodynamic wind forces. The boat cannot generate forward motion and the rudder loses its ability to steer. The boat is in irons.

The closest point to the wind that a boat can travel with full sails is called close hauled or beating. Typically the angle is about 45° to the wind. However it is sometimes possible to sail even closer to the wind depending on the wind strength, the hull and sail design, and the skill of the crew.

The point of sail directly downwind is known as a run or wing-and-wing since the sails are often set out to either side of the boat like wings of a bird.

Between beating and running is called reaching with the point nearly perpendicular to the boat called a beam reach. The area between a close hauled tack and a beam reach is called a close reach, and between a beam reach and a run is called a broad reach.

Notice also in the illustration that the different tacks are characterized as either starboard tacks or port tacks. This distinction, starboard or port, is determined by the side of the boat over which the wind passes. When the wind is coming over the starboard side of the boat, it is said to be sailing on a starboard tack, and vice versa.

General guidelines for the sheeting angle – the angle between the boom and the centerline of the boat – and centerboard depth are also given in the illustration for each point of sail. The most efficient sheeting angle depends on the size and shape of the sail, the strength of the wind, and other factors, but these guidelines are given as reference and to provide a starting point for each tack. For dinghies without a keel, the centerboard depth can be set to control side motion of the boat. It is not too critical, but in general, the centerboard is lowered as the boat sails closer to the wind.

In the center of the points of sail diagram is a typical radial speed plot which shows the relative boat speed for each point of sail. The solid line indicates the speed for a typical sail configuration using a jib as the foresail, while the dotted line gives the speed while using a spinnaker. As we’ve mentioned, the maximum driving force occurs on a beam reach, and it can be seen from the speed plot that this tack is the fastest point of sail. The spinnaker increases the achievable speed across the board, but is only operable on downwind tacks, as illustrated by the speed plot and the label showing the spinnaker usage range of 90° – 180°.

Safety Note: Sailing Downwind

Sailing downwind can be dangerous since an “accidental jibe” can occur, causing the Boom to swing violently across the boat through its maximum range of travel, potentially damaging the boom/mast or endangering crew. In the Running illustration, the Mainsail is in equilibrium on either side of the boat, making its position very unstable. A slight shift in wind direction or small turn of the boat can cause the Boom to reverse position. Many safety guidelines state that Running, or sailing directly downwind, should be avoided. The standard rule of thumb is to never sail below a Broad Reach.

Standard procedure on large boats is to tie an accidental jibe preventer to the Boom when sailing below a Beam Reach. This is simply a strong line (typically a spare dock line) tied from the Boom to a hard point on deck Forward of the Boom.