I use Sailcut, and it's the same there. The flying shape often differ from what it looked like on the screen. You need to use your knowlegde about sails and wind to get a good result. I made my first jib deeper in the top, and with some nice twist like my litterature suggested. It would probably have set nicely on a monohull, but on a cat the leech was too open.



I'll take this as a learning opportunity and have a shot:

The luff on your spi looks looser than the Gran spi. Longer with more round?
The head section on the Gran sets better, perhaps due to more panels. But the Gran spi also look like it have a horizontal cut (dart) made in the back section to tighten the aft section and the leech.
It's very hard to say from these pictures, but your spi looks like it has the same draft, but more shape to the luff section.
With a looser luff and more shape, I guess you had to go very deep to make it fly properly.

Why dont you take pictures from beneath the spi and towards the halyard block, like we do on jibs and mains? I find it easier to compare shapes that way.


I just bought an old Pfaff 1222 with triple stitch z-z and 'walking foot' for US$ 150,- Should be good for both ripstop and dacron. Issues like different tension in luff tapes and ripstop should be easier to handle with this machine. Looking forward to being able to sew zippers and luff tapes without basting them first.


The F-16 forum certainly is the most interesting and technical..