Light wind sail trim, I learnt something unexpected today

[Dockhead]

Originally Posted by Dave_S

We have had very light winds lately.

In about 4kn of true, on a Seawind 1260, tacking upwind, trimming the main, I kept pulling the traveler to windward and releasing the sheet trying to get flow across the bottom of the sail. I ended up with the boom about 5° to windward with a heap of twist, the traveller almost all the way over and the halyard just backed off enough to show a hint of wrinkle on the luff. We sailed around 3.1kn at 32 to 35 AWA without any visable tide on the marker bouy. In theory tide was in our favour but it had just turned about an hour to an hour and a half ago.

The difference in boat speed between the boom on centerline and +5° was about 1/2 a knot. About 20%

The sail shape (boom and main sheet) was just not what I expected to work, has anyone else found the same, or a better way.

That's exactly the way I do it. And it sounds like you're getting perfectly good performance.



If the leech is fairly loose, giving you a lot of twist, you need the traveler to windward to get the right angle of attack for the sail as a whole. You'll know that the mainsail is exquisitely sensitive to angle of attach, when sailing hard on the wind, so play that traveler.


Note that the optimum amount of shape in the sail will be more and more as the wind speed drops but then less again as it gets really slow, like under 5 knots. Counterintuitively -- you have to flatten the sail a bit again in very light wind, to keep the air flow attached when it's very slow. So hardening outhaul and mainsheet or vang again slightly.


Don't be afraid to experiment with counterintuitive adjustments, especially in light wind, where things don't always work the way we expect. I've been too conservative my whole life, which has made me a slow learner. I would approach it differently if I could do it over again -- and I might have learned stuff decades earlier than I actually did