Hi Rolf,
I'm back from my sailing weekend and the tests results are quite encouraging. I did increased the prebend from 1" to 1.5" and went out sailing. Wind was very light, 3 to 5 knots, going upwind, I slowly cranked the downhaul by small increment pretty much up to max and that top leech telltale finally did start to stream about 50% of the time. Altough I'm pretty bad at the seat of the pant feeling, my pointing seems better(guys at the club agreed), but also I felt the boat was running a bit faster, that choking the boat feeling when sheeting hard was gone. My lower leech telltale was still hooked to leeward all the time so I tought I should try to increase sprearders rake to flatten a bit more this part of the sail.
Then back on the beach and up in the ladder to reach the spreaders to find out that the adjustments are seized up. I dont want to compromise my sailing season, I'd rather sail with a badly tuned boat than no boat at all. So that will be a winter project. I did measured the spreaders rake, I'm already at 2.5". Nacra 20 tuning guide recommend 2.6" for light crew. Since I'm all alone on the boat and the mast seem quite stiff, do you think it is safe to go beyond that recommended setting, may be 3".
I tried trough the site search engine to find out more about mast and sail tuning but I had a hard time to get good result. Any clue how to refine my search? I would really like to read about the subject.
Thank again for your help.
Denis