WD-40 will get rid of the glue residue...let it sit for at least an hour, then scrub with BRONZE wool...easy to find at any big box or hardware store.
Never use steel wool on a boat...it rusts. May not matter if the little bits that break off just fall oo ground or into the water, but you definitely don't want to use steel wool for any project IN the boat.
--Peggie
Peggie mentioned WD40 and
yes it's a great adhesive remover, but use it only after you've removed the vinyl.

However, I'd never use bronze wool on any fiberglass that I want to shine up after.
This is a 3-step job:
1) First step is optional: Use the heat gun or hairdryer with a plastic scraper to lift the vinyl. Don't worry too much about getting it all off, and don't worry about removing the adhesive at this stage.
2) THIS is THE stuff you want for this job, it will chemically convert the adhesive to a compound that has the consistency of Ivory bar soap, so it can be easily removed without pushing it around the surface. You can buy it online or a well stocked auto supply store where they sell body shop supplies.
3M™ Woodgrain and Stripe Remover | 3M United States
3) Follow up the woodgrain/stripe remover with 3M Adhesive remover and/or WD40, Interlux 202 fiberglass solvent wash, or other thinners that remove the stuff.
4) Follow up the whole process with compound for a clean shine before you apply the new stripe. Then wax to protect the new stripe and the whole finish.