Patch Method
In order to stabilize the patch and sail while you sew it, use spray adhesive you can get at a store like Michaels or maybe hardware stores, Wal Mart, etc. Made by 3M called Super 77 Spray Adhesive. With the sail flat and no wrinkles spray the adhesive on one side of the patch then glue it to the sail. Now you can sew it without the sail or patch shifting around. If it is just on a single ply section of the sail a regular machine should work but you will need UV thread. A zig zag stitch will be prefered to lock the threads on the edges so they don't fray. I have some scrap sail material, I can throw a little in an envelope if you send me your address as a personal message.