This was nicely illustrated. The critical reason for paying attention to this is because true wind speed varies with height, with slower wind speed at the boom compared to the top of the mast. Of course boat velocity is identical along the whole mast. So, the vector addition of those two gives a difference in both apparent wind speed AND apparent wind angle depending on height, with a tighter point of sail at the boom compared to the top of the mast. By loosening the vang and mainsheet, and raising the traveler, you twist the sail to more closely match sail shape with apparent wind angle along the whole mast. This applies especially when boat speed is slower.

There is a notable word track that the poster used here (at 1:15) when he spoke of removing twist by tightening the boom vang. He said we are "pulling the boom down". This is important (especially for those new to sailing) because the amount of twist is directly related to your boom height (or up/down angle). And you control boom height either with boom vang (when the boom is out) or traveller and main sheet (when the boom is in over the traveller).

@NauticEd

6 ай бұрын

Thanks for your comment

Thanks for this. Very helpful.

The angle of attack is more a function of pulling the sheet. I would think that changing the twist is changing the camber of the airfoil until it starts spilling air. Angle of attack is the angle between the chord line and the relative wind.