Just to update those who took an interest in my sail building attempts:

Thanks for your input Marcus, but I hadn't put a luff line in when I built the kite. Perhaps next time....

Anyhow, as I said I would, I unstitched the luff tape down to about half height (I figured that the bottom half of the spin didn't look too bad). Then I opened up the upper horizontal seam through two panels. I made a small dart of ripstop about an inch deep and just over a panel wide and then re-stuck the panels. I then resewed the luff tape, taking extra care that the tensions in spin cloth and tape were the same.

I tried it out last weekend (had to scrape the frost and break the ice off the boat ) - winds were 'challenging' at 12 - 35 knots! - and although it IS better - it's still not quite right. I now suspect that I may have built too much twist into it, as although it's basically the same dimensions as my Landy kite, it looks totally different and the sheeting angle doesn't look right. The foot comes tight waaay before the leech, so I'm going to rig up a sort of adjustable sheeting arrangement and have a play with that.

BTW the sail was designed on Sailcut 6 and the shape is the result of discussion with Dave Tugwell at Datchet who also posts on this forum from time to time. David has already built quite a few spinnakers for his Stealth (and for other people too!) so he's been a great help. However, he is still experimenting as am I.

The panels were cut professionally and I simply stuck and sewed the whole thing together. Next one though is going to be wholly sewn as I didn't like the end result of the sticking process - it's too easy to leave an edge of tape showing and then you've got to de-sticky it with talcum powder, also alterations and adjustments are less easily done when you've got sticky remnants to deal with.

I'll keep you posted on progress - or lack of - (if you're interested)