: The wood was dry so I don't think it is the frame shrinking.

Perhaps not, but that's often the cause of slack skins on boat with steam-bent ribs. Once a skin is coated, it takes very little change in the frame for it to go slack.

: This is more annoying than nylon to me. We went out with the two Curlews
: today and nylon boat honestly looked better than the polyester boat. The
: nylon doesn't loosen up nearly as much as it did 6 months ago. I thought
: polyester was going to be "The Stuff" but this has not impressed
: me much frankly. Especially since it is so hard to sew.

What polyester did you use. Of the three I've used (9 oz Dyson, 10 oz Tacoma, 13 oz Dyson),the only one I found hard to sew was the 13 oz.