Apparent wind

Apparent wind is the wind speed and direction experienced onboard a moving vessel. Unlike true wind, which represents the atmospheric airflow over a stationary point on the Earth's surface, apparent wind is the result of combining true wind velocity with the boat’s speed and heading. Mathematically, it is the vector sum of the true wind vector and the headwind vector generated by the yacht's own forward motion. For skippers and crew, understanding apparent wind is fundamental because sails react exclusively to the apparent wind, not the true wind. Wind speed at sea is typically measured in knots (1 knot = 1.852 km/h or 0.514 m/s), while direction is specified by the apparent wind angle (AWA) in degrees relative to the yacht’s centerline, from 0° (dead ahead) to 180° (dead astern). An onboard anemometer mounted at the masthead measures this relative flow to assist in precise sail trimming. When sailing upwind or close-hauled, the vessel's movement increases the apparent wind speed and shifts its direction closer to the bow, forcing the crew to trim sails tighter. Conversely, when running downwind, the boat moves away from the wind, reducing the apparent wind speed and shifting the angle toward the stern. Consequently, high-performance craft can sail faster than the true wind speed by generating significant apparent wind on reach courses.