Marine Glossary

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TWA (true wind angle)

The angle between the heading of a vessel and the wind direction, usually specified as between 0° (dead ahead) and 180° (dead astern) with the label port or starboard. Alternatively, the wind angle can be specified as a "relative angle," wherein the starboard beam is at 090 relative, the stern at 180 relative, and the port beam at 270 relative. A wind of 150° on the port side would be at a relative angle of 210. These relative specifications of wind angle are used on USCG exams, but they are confusing to use underway, especially for sailors who must truly keep track of where the wind is relative to the bow in order to sail the boat.

The wind angle can be specified as an apparent wind angle or a true wind angle. The true wind angle is always aft of (larger than) the apparent wind angle for a moving vessel. The true wind direction is figured by adding or subtracting the true wind angle to the vessel's course. See apparent wind and true wind. See RES-5 for further discussion.