Weather gage
From Free net encyclopedia
To have the weather gage describes the favorable position of a sailing vessel relative to another with respect to the wind. The term is from the Age of Sail, and is now antiquated. It is any position upwind of the other vessel. An upwind vessel is able to maneuver at will toward any downwind point, since in doing so the relative wind moves aft. A vessel downwind of another, however, in attempting to attack upwind, is constrained to trim sail as the relative wind moves forward and cannot point too far into the wind for fear of being headed. In sailing warfare, when beating to windward, the vessel heels under the sideward pressure of the wind. This restricts gunnery, as cannon on the windward side are now elevated, while the leeward gun ports aim into the sea, or in heavy weather may be awash. A ship with the weather gage, turning downwind to attack, may alter course at will in order to bring starboard and port guns to appropriate elevations. The term has had a literary rebirth in the popular seafaring novels of C.S. Forester, Patrick O'Brian and Alexander Kent.
The concept of weather gage is still useful in modern yacht racing, although it is hardly ever referred to by that name. The sails of a boat disrupt the wind to leeward - this disruption is often called "dirt" or "dirty air". An overtaking boat on a downwind course can position itself to focus its dirty air on the boat ahead of it. Conversely a boat on an upwind course may find itself trapped in the dirty air of a boat immediately to windward. However right-of-way rules, which give priority to the leeward boat, can make it advantageous to be the boat without the weather gage especially just before the start or when the boat to leeward can point higher into the wind.