Simon,

no indication from the sailmaker about how much 'slack' there would be when sailing. I always tought about this 'slack' in spis as negative luff round, but perhaps there is some other terminology that should be used.


Do you mean John, as in John Pierce?

10% 'slack' on a 8000mm long luff.. That is a lot of 'slack', if that is how it's calculated <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />
1% is more like what I would expect. If you pulled the luff tight and the spi was not designed for it, I would expect draft to move forward. With some real pressure in the sail, draft should move somewhat aft, but how much..
There is much fun to be had with saildesign, and especially with relatively free flying sails like spis.


Take care with your new boat, wich is much to beautiful to damage so early!