perhaps you can take your boat to a sail maker and rig it.
this way you can find out what is the right measurement for your setup and perhaps order a custom spin.

I know several people who did this with great results.


you should have a bit of flexibility (on the luff size) with the possition of your pole and amount of prebend in it. When i used a f18 spin (on my 30' mast) my pole was Very high. Now that i have a Tornado spin.. it is pretty low, with minimal prebend.