Joe - you may want to look into "Peel Away" paint remover. They have a marine product that is very effective and safe for the gelcoat. I have used the product it it works very well. You can get it in 5 gallon pails. Here is some information on it. BTW only use their marine product on your boat other wise you wont have gelcoat left.

PEEL AWAY MARINE SAFETY STRIP
PEEL AWAY MARINE SAFETY STRIP is an environmentally safe paint remover used for the removal of bottom paint from fiberglass, wood and metal boats without any damage to the surface. It will remove up to 10 layers of bottom paint in ONE application. The product also works well at removing varnishes, polyurethane, shellac etc from fine wood surfaces i.e. teak, mahogany etc. Coverage is 40 sq. feet per gallon. Marine Application

http://www.dumondchemicals.com/paint_remover.htm