The surface of the hull is gel coat, which is sprayed into the mold, and the laminate built up behind it. Gel coat is about 15 mils thick, as compared to about 3 mils for paint. Whether or not you have to remove gel coat when making repairs depends on what you are trying to do. Gougon Brothers publishes two good booklets on frp repair which can be ordered from West Marine, and are shown in their catalog.
I would recommend using epoxy rather than polyester to do the repair.
Be aware that it is impossible to spray gel coat without getting orange peel on the free surface, which requires considerable sanding. If you are repairing a large area. you would be better off with paint.
Mort
