Sailing into the wind

Sailing into the wind is a sailing expression that refers to a sail boat's ability to move forward despite being headed into (or very nearly into) the wind. A sailboat cannot make headway by sailing directly into the wind (see "Discussion," below), so the point of sail into the wind is called "close hauled", and is 22° to the apparent wind.

Sailing into the wind is possible when the sail is angled in a slightly more forward direction than the sail force. In this aspect, the boat will move forward because the keel (centerline), of the boat acts to the water in as the sail acts to the wind. The heeling force of the sail is balanced by the force of the keel. This keeps the boat from moving in the direction of the sail force. Although total sail force is to the side when sailing into the wind, a proper angle of attack moves the boat forward.

Another way of stating this is as follows:

Alternately, sailing in the direction from which the wind is coming is possible through sailing at forty five degree angles to the oncoming wind and alternating the direction of those angles. This is called "tacking." Although this method requires the boat to physically move farther to reach a given point, it is often the quickest way to move in a given direction overall.

The points of sail clarify the realities of sailing into the wind. One of the points of sail is "Head to Wind." A boat turns through this point on each tack. It is the point at which the boat is neither on port tack or starboard tack and is headed directly into the wind. However, a boat cannot sail directly into the wind, thus if it comes head to the wind it loses steerage and is said to be "in irons." Thus boats sailing into the wind are actually sailing "Close Hauled" (i.e., with sails tightly trimmed).

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Wikipedia