Tacking (sailing)

Tacking from starboard tack to port tack. ① on starboard tack, ② turning to windward to begin the tacking maneuver or "preparing to come about", ③ headed into the wind where momentum carries the vessel forward, ④ powering up on the new port tack by sheeting in the mainsail, ⑤ on port tack.

Tacking or coming about is a sailing maneuver by which a sailing vessel turns its bow through the wind so that the direction from which the wind blows changes from one side to the other. One way the boat moves into the wind is by making their sails curved. The wind moves faster over the convex side of the wing that the concave side because it has farther to go in order to get around (thus creating an air foil). This causes less pressure on the convex side resulting in a force on the ship towards the convex side of the sail.

The keel can then use this motion to help travel into the wind. For example, if a vessel is sailing on a starboard tack with the wind blowing from the right side and tacks, it will end up on a port tack with the wind blowing from the left side. See the image at the right; the red arrow indicates the wind direction. In practice, the sails are set at angle of 45° to the wind for conventional sailships and the tacking course is kept as short as possible before a new tack is set in. Rotor ships can tack much closer to the wind, 20 to 30°.

Technical usage

If the wind shifts, the tack needs to be realigned

Tacking is distinct from jibing, where the ship's stern passes through the wind.

Tacking is sometimes confused with beating to windward, which is a process of beating a course upwind and generally implies (but does not require) actually coming about.

When used without a modifier, the term "tacking" is always synonymous with "coming about"; however, one can also "tack downwind"; i.e., change tack by jibing rather than coming about. Racing sailboats do this because most modern sailboats (especially larger boats with spinnakers and a variety of staysails) sail substantially faster on a broad reach than running dead before the wind. The extra speed gained by zigzagging downwind more than makes up for the extra distance that must be covered. Cruising boats also often tack downwind when the swells are also coming from dead astern (i.e., there is a "following sea"), because of the more stable motion of the hull.

Beating

File:Jibing Intervals 2.jpg

Depending on the situation, different intervals between tacking can be used. This does not influence the total distance travelled.

Beating is the procedure by which a ship moves on a zig-zag course to make progress in the direction from which the wind blows. No sailing vessel can move directly against the wind but that may be the direction it wants to go. Beating allows the vessel to advance against the wind.

A ship that is beating will sail as close to the wind as possible; this position is known as close hauled. In general, the closest angle to the wind that a ship can sail is around 35 to 45 degrees. Some modern yachts can sail very near to the wind, while older ships, especially square-rigged ships, were much worse at it.

Thus when a ship is tacking, it is moving both upwind and across the wind. Cross-wind movement is not desired, and may be very much undesirable, if for instance the ship is moving along a narrow channel, or the destination is directly upwind.

Therefore the ship changes tack periodically, reversing the direction of cross-wind movement while continuing the upwind movement. The interval between tacks depends on the lateral space available: in a small navigable channel, tacks may be required every few minutes, while in the open ocean days may pass between tacks, providing that the wind continues to come from the same general direction.

In older vessels that could not sail close to the wind, beating could be a tiresome process that required sailing a total distance several times the distance actually traveled upwind.