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Te Hau said..
Make sure you're not over sheeting the sail. Many sailors do this. As you climb upwind your angle to the wind is changing and the sail needs to be sheeted out slowly to match the changing angle to wind.
I agree with your suggestion, but not with the "why" you give.
As you point higher into the wind, the apparent wind angle moves towards the nose of the board. That is true even after taking into account that the speed drops at higher angles. So adjusting to the change in apparent wind angle would require sheeting in
more.
In reality, though, sheeting out a bit can give for better upwind speed. This is counter-intuitive when looking at the apparent wind direction. I think the reason sheeting out works can be found by looking at the
direction of the lift that the sail generates. If you're sailing at the speed of the true wind at an angle of 45 degrees, then the true wind speed is 22.5 degrees. Being fully sheeted in for this angle means that most of the sail's lift is
perpendicular to the direction of travel, so it needs to be re-direction using the fin and the leeward edge of the board. Opening up the sail a bit directs the lift of the sail more forward.
If you're using an adjustable outhaul and pull it in when going upwind, then you could also just look at the angle of the front-most part of the sail (roughly the luff sleeve in slalom sails). You could imagine that most of the forward-directed force is created there (that's a bit simplistic but not entirely wrong). If your changing course from beam reach to going hard into the wind (at 45 degrees to true wind), and we assume your board speed drops from 1.2x wind speed to 1x wind speed, then the apparent wind angle decreases by about 17 degrees. If you tighten the adjustable outhaul a lot for this course change, reducing the profile depth of the sail, the angle of the front-most part of the sail is reduced. That means rather than sheeting in 17 degrees more to adjust to the apparent wind, you would need to sheet in significantly less.