WinWind
Chapter 3 · How a sail works
How Does a Windsurf Sail Work? Lift, Sheeting and Apparent Wind
Lift, sheeting, apparent wind
How a sail works — step by step
A sail is a wing
Wind flowing over the curved sail makes lift, like an aircraft wing.
The daggerboard resists the sideways part, so the board moves forward.
Sheet in to go
Sheet in: the back hand pulls the boom in, the sail fills and you speed up.
Try it: pull the stick down on a phone, or press S.
Luffing vs stall
Too loose: the luff flaps (luffing) — no power.
Too tight: the flow stalls — slower.
Fastest is just past where the flapping stops.
Quick quiz
- Sheet in a little ✓ Answer
- Sheet out a little
Apparent wind
Once moving, the wind you feel = true wind + wind from your speed. That is apparent wind.
The faster you go, the more it comes from ahead, so sheet in more.
Quick quiz
Sailing downwind, should the sail be more open or more closed?
Quick quiz
- More open (sheeted out) ✓ Answer
- More closed (sheeted in)