I spent 5 days on the hard last November removing vinyl stripes including some wide curves running all along the sides. It was 20 years old and faded and cracked. I must have tried every solvent known to man and every technique posted on forums. The problem with old vinyl is that the vinyl tends to be UV damaged and fragile so it won't peel off in a continuous strip. On the other hand, the adhesive is very tenacious and difficult to remove. In the end, the technique that worked the best for me was a razor blade window scraper in one hand, and a spray can of Goof-Off Graffiti Remover https://www.homedepot.com/p/Goof-Off-18 ... /202676194
in the other hand and a rag hanging out of my pocket. The Goof Off Grafitti remover is very different than the standard Goof Off or other similar products. It really liquifies the adhesive better than anything else I have tried (acetone, lacquer thinner, Isopropyl alcohol, WD40, PB Blaster, heat guns, etc). So, the specific technique is to spray a short section of vinyl with the Grafitti Remover and then run the flat razor under the vinyl, removing as long of a strip as you can. Of course, you need to keep the blade flat and at the right angle so you don't scratch the gel coat. I was very careful at first until I got confident in the technique. I did not scratch the gel coat at all. There will be liquified goo on the razor blade, so wipe it on your rag and repeat. When I was done removing the vinyl, there was still adhesive residue where the vinyl was. So, I simply went back over it with the Graffiti remover and razor blade. It was amazing how much adhesive came up on the blade and I would wipe if off on the rag after each pass. For the final removal of the last bits of adhesive, I would spray the area and wipe with a rag. There were some areas that seemed to resist even the Graffiti remover and razor blade and for that I used the 3M Stripe-Off wheel on a power drill. It is like a giant circular eraser on a wheel and is specifically designed for removing vinyl stripes. It will not damage the gel coat. I can attest to that.https://www.amazon.com/gp/product/B0006 ... UTF8&psc=1
When I had all the vinyl and adhesive removed, the gel coat under the vinyl was pristine and bright white compared to the rest of the oxidized gel coat. So I then sanded and compounded and polished the entire hull. When done, you can't really see where the stripes were.