I have a jib for my 18 that the wind caught. It shredded the Mylar, but the Nylon looks brand new. Can I have new Mylar sewn in? Or can I seal the sail with something that will hold the wind? I don't race, I have a good spare but it is plain white, and I loved the colors on the other one.
You have a few choices:
1 - Send it to a sailmaker. He will replace the entire panel.
2 - Replace the panel yourself, using nylon.
3 - Stick it up with Duct tape - but make sure it's dry first!!!
you can go to Murrays or west marine and get clear sail repair tape. It will get you through the season and then you can have the mylar replaced.
When you say 18? The Hobie 18 SX came with mylar/dacron laminate sails, is that what you have?
There is no cure for mylar delamination, sorry. You could just keep using it until the sail tears apart at the seems.