Re: removing hull numbers
jf, you can find "decal remover" at any auto parts store. Or use naphtha, which is the original solvent, or something higher end if you want to move faster. The companies that make the vinyl all say to use a heat gun, or the remover, or there's 3M's "eraser" wheel that you can buy in auto body shop supplies. That's a hard rubber grinding wheel you put in a drill, it will abrade the vinyl off without damaging the hull finish. I'd suggest the heat gun first, and patience. Chemicals on a vertical surface is always a mess.
If you go to a sign shop as Chuck suggests, make sure they are using exterior rated and guaranteed vinyl. The good stuff will have a 5-7 year guarantee on it. A white "plaque" with dark letters on it will hide all the old sins, because the old numbers WILL leave ghosts behind. The gelcoat has worn down around them, you'd need to refinish the hull to hide that.