You're unlikely to remove the remains of Mother Nature's crazy glue
(courtesy of barnacles) with a chemical attack -- at least I've never
heard any verifiable claims to such. I did mine with a 2" putty knife and
a LOT of effort. Scrape, scrape, scrape. This proved gentler to the gel
coat than any other approach -- most of which involved abrasives or
ineffective chemicals. Most important, if you do clean down to or into
gel coat, use a chemical primer paint designed for gelcoat before you use
any bottom paint. With such, adherence is perfect. Without, it usually
stinks.
Regards,
Bill Combs
WWP 19 #439, "Ursa Minor"
Fort Walton Beach, FL
ttursine@gnt.net