Apparent Wind Calculator

What kind of Asymmetric Spinnaker should you buy?

It depends on how fast your boat can go. The apparent wind — the strength and direction of the breeze seen by your sails — depends on your boat speed.

The faster you go, the further forward the apparent wind. Go fast enough, and you'll always be close-hauled, even down wind!

For downwind sailing in light wind with a cruising asymmetric spinnaker (aka gennaker) start by sailing on a beam reach to build up speed. As the boat speeds up, the apparent wind moves forward, and you can steer deeper. If the boat slows down or the wind weakens, steer a little higher for more power to rebuild boat speed. If you keep your speed up, the apparent wind will stay forward enough that the spinnaker isn't blanketed by the mainsail, even if you are sailing as low as 155 degrees off the true wind!

Use the calculator below to experiment with the relationship between true wind, apparent wind, and boat speed. Enter your values, then press the "Recompute" button.

This page appears courtesy of, a great reference and resource website for sailing.

Enter your Inputs

Wind Angle:  deg True Apparent
Wind Speed:  knots True Apparent
Boat Speed  knots


VMG to wind -2.9
True Wind Angle 155°
Apparent Wind Angle 131°
True Wind Speed 6.0
Apparent Wind Speed 3.4
Boat Speed 3.2
Boat speed as % of true wind speed  53.3
VMG as % of true wind speed -48.3

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