Apparent Wind Calculator

The wind on your face while sailing is rarely the true wind the forecast reports — your own motion adds to it. Set the three numbers below and watch the vector triangle that produces the apparent wind speed and angle your sails actually feel.

As boat speed increases, the headwind created by your own motion adds to the true wind, and the combined apparent wind swings forward of the true wind direction — which is why sail trim gets tighter as a boat accelerates on a reach. Sailing dead downwind is the exception: there, going faster only makes the apparent wind lighter.