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vfourpointone-flashxhigh — 05 / 05

Sail Trim

The wind you feel on the water is not the wind in the forecast — it is whatever is left after you subtract your own motion. Steer, sheet, and round the windward mark before the shift runs away with you. The polar chart in the corner is the honest answer to "how fast can this boat go at this angle".

boat speed0.0 kn
apparent—
VMG to mark—
elapsed00:00

Steer with the arrow keys and trim the sheet. The mark sits upwind; nothing sails straight into it.

Trim

The physics are the usual ones. Apparent wind is the true wind vector minus your own velocity, so it hauls forward and strengthens as you accelerate. The sail makes lift and drag from its angle of attack, which is the apparent wind angle minus your sheet; drive is the part of that left over pointing where you want to go. Nothing works inside about 35° of the wind — that is the no-go zone, and the polar chart in the corner shows exactly what the boat will do at every angle, solved with the same equations you are sailing with. Keys: ← → steer, Q E or the sheet dial to trim, Space pause, R restart.