Free apparent wind calculator
Explore true and apparent wind with adjustable heading, boat speed and wind speed. See the vectors, calculation, guided examples and free questions. It is an independent revision aid, not official RYA training or assessment.
Direct answer
Apparent wind is air movement relative to the moving boat. It combines the true airflow with the opposite of the boat’s velocity. Direction matters: running directly downwind reduces the wind felt aboard, while forward motion on a beam reach brings it forward.
Learn the wind
Change heading, wind and boat speed. See why the wind felt aboard differs from the wind over the water.
Blue solid: true airflow + grey dashed: boat-motion contribution = orange solid: apparent airflow.
Arrows point where air travels to. Wind angles name where it comes from. Collinear vectors overlap.
Clockwise from the wind source. Arrow keys make 1° changes.
Try a heading
Wind-from component ahead = 10 × cos(-90°) + 5 = 5.00.
Wind-from component to starboard = 10 × sin(-90°) = -10.00. A negative value means port.
Apparent speed = √(ahead² + across²) = 11.18 kn.
Still water, no current or leeway. Boat speed is an input, including when head to wind; this model does not predict a sailable heading or achievable speed.
An independent Compass introduction for new sailing crew. Read with the skipper’s instructions for your actual boat and conditions. It does not award a qualification or assess practical competence. Source check: 3 September 2026.
In the boat’s frame of reference, forward motion adds an airflow from ahead. On a beam reach, 10 knots of true wind and 5 knots of boat speed combine to give about 11.2 knots of apparent wind at 63 degrees off the bow. The square root of the summed squared components gives the speed.
Only when their velocity vectors match does apparent wind become zero. In this model that means running directly downwind at the true wind’s speed. At zero apparent wind, direction is undefined. Selecting a speed here does not imply a sailing boat can achieve it.
The model assumes still water and no leeway. It does not calculate current, gusts, mast motion, sail forces or trim. Wind speed is relative to the water and boat speed is through the water; do not mix ground-referenced wind and boat speed without converting the reference frame.
Use this canonical URL in club newsletters, lesson notes, or student revision plans.