@DanHulme You didn’t tag me, so I just noticed your message. When you say it moves stagnation point downwards are you referring to the curve at the leading edge? I think the curve he’s referring to is the entire sail. I agree that those points are true. An airfoil shape is better at creating lift.

@DanHulme And when you say “upwind” I presume you mean at an angle greater than 90°? I don’t know a darn thing about sailing.

I thought the sail produced lift nearly perpendicular to the wind. It can’t actually produce an upwind force. It’s the angle of the boat’s keel that turns that perpendicular force in an upwind direction. I still think a flat, rigid sail could do that. It just won’t be as efficient, so the upwind angle would be shallow and require a lot of tacking.

@TomMcW no, I mean the trailing edge stagnation point

@DanHulme I'm confused then

The classic aerofoil shape, shared by a sail, moves the trailing stagnation point lower than it would be with a flat surface. It's something to do with the Kutta-Joukowski theorem, but my maths isn't up to that

I guess I'm just not going to completely understand lift creation. There are just too many variables going on.