Thanks heaps for your feedback guys. The boat is a 6 metre Jarcat Catamaran. Home built from ply. Not allowed to give you a link apparently as I haven't posted enough on this site. BUT if you google Jarcat Marine you'll find it
I was going to use 4oz Dacron, we don't get out a whole lot and I thought it would be easier to sew up. Also, I thought it might stretch a bit over time anyways creating draft. The alternative is to simply add some Luff curve and some Foot curve like they did in days past. I Have a copy of "Make your Own Sails", it is a bit dated but I am sure it would work fine still - like I said, I'm cruising not racing.
I am interested to understand how important adding draft is to a head-sail, and how much performance would be lost by not adding it. From what I am reading I should add a little at the very least, is this correct? And then I could add some foam etc to the middle of the luff to take up the bagging that would occur. Clearly I have little idea what I am doing here so please tell me straight if I am missing the point, I am sure I will appreciate it when I am out sailing using my DIY Genoa.
Thanks again in advance