Gel coat is the outer layer of the fiberglass - usually white in color, but often is different colors.
You must be thinking of a wax or something, as gelcoat would be used over bare fiberglass, not paint.
http://www.youtube.com/watch?v=1ez5PetDp64&feature=related
http://en.wikipedia.org/wiki/Gelcoat
What is gel coat and what is its purpose?
Someone has painted the boat I now have and I am wondering if it has or needs gel coat.