I often get asked what is the best way to remove bottom paint?
For me, there's no good way to completely remove bottom paint. Every method risks damaging the underlying gelcoat. Sanding works until you reach the fiberglass, then you're sanding the gelcoat, which you don't want to do unless you are repainting. Chemical strippers can be even worse. The kind you find in paint and home-supply stores cannot tell the difference between paint resin and polyester resin, so when they get through the paint, they will literally start dissolving your boat. So-called fiberglass-safe strippers can work, but are only safe if you're meticulous in how long you leave them on, which is often insufficient to fully remove the paint. That brings you back to sandpaper. Boatyard staff may recommend sandblasting, but sandblasting fiberglass boats damages them, no ifs, ands, or buts. Blasting with a softer medium, such as baking soda, is probably the gentlest removal option, but you're going to have to find someone who does this and it will not be cheap.
So typically I recommend not removing the bottom paint just because you no longer need it. If the color bothers you, then prep the bottom and paint it with white bottom paint (Pettit Vivid). This will be virtually undetectable except by close inspection, and can actually make the bottom easier to keep clean, and that could be beneficial if you use your boat for vacations where it stays in the water for days rather than hours.