I have just had a look at your work, and have some comments/questions.

1: I think 18deg twist is excessive in the design. I would think 8 to 13 to be better. We used 8deg on the Tornado main we buildt and that was about right, perhaps a litt much for our conditions.
2: 5% draft is very flat in my opinion. I would not go below 10% draft and probably build it with more draft for our crew weight and conditions
3: I would have pushed the draft forward a a fair bit to compensate for the rotating mast working as a leading edge of the foil.
4: You probably want to work some more on the luff curve. 35mm at 45% dont sound like a beachcat mast. You need to match the luff curve of your sail with how your mast bends when sheeting it in. Otherwise, your sail will not set very well and give poor speed. You can either suspend the mast between two points and hang 10kg buckets on to it before you measure, or hoist your old sail, sheet it in (take care to rotate it) and shoot some digital photos. Use Photoshop or Gimp (open source) to match the bending properties of your mast with your sails design. Either way you choose, you need to think about how the mast bends to make the luff curve of the sail match it.
5: If you decide to add some draft, consider how your jib will interact with the main. You probably want the main to have less draft further aft where the airstream from the jib influence the airstream over the main.

I always choose to work with a crosscut layout in sailcut, it makes it easier to see how the draft is positioned. Afterwards I switch to tri-radial or whatever cut I want to use. I'll try to attach two screenshots taken from 87deg above to demonstrate the differences in shape.

I'll try to attache the design file for Tornado mainsail we buildt. It should be a fair base to work on your Hobie18sx design once you alter the luff curve to match your mast and compensate for your overlapping jib vs. our selftacking. I would do some changes to the design if we were to build another one, but nothing major.

Tornado main screenshot: http://www.catsailor.com/bb_files/101528-tornado-main-25-04-05.gif
Hobie18SX original: http://www.catsailor.com/bb_files/101528-hobie18sx-original.gif
Tornado main saildef file: http://www.catsailor.com/forums/download...p?Number=101528