True / Apparent Wind Calculator

The wind you feel on board is almost never the wind on the water. A 10-knot breeze across the beam feels like 14 knots when you're motoring at 8 knots into it. This calculator solves the wind triangle in both directions.

What it does

Pick the wind you know, and the calculator computes the other.

• True → Apparent: given the actual wind and your boat speed, what will the instruments read?

• Apparent → True: given what the windex shows, what's the real wind out there?

The chart shows both arrows on a bow-up view alongside an inset velocity triangle that makes the underlying maths visible. Velocity Made Good (VMG) to windward is computed automatically.

When to use it

• Sail trim: separate the apparent shifts caused by boat motion from a real windshift.

• Race planning: work back from forecast true wind to expected boat apparent so you can size your headsail before the start.

• Weather routing: convert your masthead reading back to the underlying wind for plotting.

• Teaching: show how the apparent wind always shifts forward as the boat accelerates.

Notes & conventions

• All angles are measured from the bow, clockwise 0° = ahead, 90° = stbd beam, 180° = astern, 270° = port beam.

• The Beaufort number is shown alongside the speed for quick reference.