There are two easy ways to remove the vinyl, I've done thousands.
1- The heat gun as mentioned above, but if there's any glue left use Wax, Grease, and Silicone remover (pre-kleeno) on the glue rather than acetone or lacquer thinner.
Trust me, it's a lot easier because it removes most of the stickiness of the glue so you can just brush it off with your fingers where it stays on the boat.
2- A stripe eraser in a drill. The 3M flap style won't work as well in a drill as the solid type made by Astro and others because drills are too slow.
These products are available at autobody supply stores.
All of the sanding
and polishing advice above is good.