If one thinks about unified shape of jib and main then the main bending (bag, sag?) should be nearer the mast in 2up sail. In 1up sail there is only main and the curve of main can be spread out more evenly to get more efficient shape making it flatter, because the wing shape is shorter (thus the sag (?) cannot be made as deep, not just because you want lose some power from sail). And in flatter sail pulling the downhaul should have more effect on lower part of sail than with fuller sails.

In Rolf's pictures it seems to me that sails are cut this way, of course A-cat might have used the donwhaul lot more and the F18 might still be looking for more power. It's hard to know differences without being able to pull the strings yourself <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I should have looked the English terms somewhere and I should have written this longer so that I wouldn't look like total idiot, so don't be offended if this post is somewhat confusing <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

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Valtteri