Heat gun & Goo-off. Also debadges your car and trucks with perfection. Heatguns are basic to figure out. Start small and work slowly, until you understand the operation. After that, it's a breeze...
another idea if it is a new boat and a semi dark color, park it in the sun for a few hours. They peal right off. What J said about the heat gun True that. Forgot to say that in my original post sorry.
On my SAN 210, the decals peeled off without using a heat gun. It took a while though because the decals kept breaking in little pieces. I cleaned up the adhesive residue with cleaner wax. Take your time and be patient.
A heat gun is too much. A hair dryer is just about right and will get it loose. Just don't hold the hair dryer in one spot on high for too long. Goo gone for the leftovers.