[Gerry Zagorski]

If you are seeing a shine under the paint that's your gelcoat. What most people do before applying anti fouling paint it just sand lightly to give the paint better adhesion so your gelcoat should be fine.,

If you are going to trailer the boat from now on, I wouldn't bother repainting the hull. I'd take it down to the gelcoat with some paint stripper.

Rather then go to a marine store and pay more, go to an auto parts store and get some Kleen Strip paint stripper for fiberglass. Don't get the stuff for metal, it has to be the one for fiberglass or you might damage your gelcoat. It's probably going to take a few applications but it's better then trying to sand it all off.

Most bottom paints are toxic so wear gloves and put a tarp underneath the boat to catch any loose paint. If you sand at all make sure an wear a mask.