Gelcoat Experts - Removing Painted Pinstriping

We are restriping our houseboat, and running into some problems. The boat is a 1995 model, and the original stripes were painted on. We want to go back with vinyl stripes. I guess the exposed white base gelcoat has deteriorated over time. We can buff the old stripes completely off, but you can still see ridges where they were. These ridges are visible through the new vinyl striping when you lay it down.

We have a box of striping samples and we're really just getting started with this part, so pretty much anything is still on the table except for keeping the original stripes (ugly as hell colors and now ruined anyway).

We tried sanding a small area with 240 grit on a 7" rotary sander/polisher, at a pretty low speed. It worked great for knocking the ridges down and taking the color off, but is obviously way too aggressive to do more than a small test area (it was the finest we had handy). We are thinking of trying 400 grit or finer on random orbital sanders. I can't find anything finer than 240 grit for the 7" rotary, and 400 for a random orbital.

This is a 16x72 foot boat, so anything we do needs to go pretty fast or it's going to take us forever. Hand sanding really isn't an option - there are only 3 of us, and I have a blown knee right now.

TIA for any help...

I would try a foam pad on the with either 3M Finesse IT polshsing compound or if that is agressive enough 3M Heavy Duty Rubbing Compound. Even rubbing coupound will leave a dull finish and requires the Finesse IT polishing compound to return the complete gloss of the original finish.

If it is actual Striping/Lettering Enamel like "One Shot" brand, which I doubt because it's too big of an area to stripe by hand, but Easy Off oven cleaner will take off striping enamel. You could try a small spot but like I said I doubt they would use Striping/Lettering Enamel for an area that big. It was most likely sprayed acrylic or urethane enamel. There is a product for stripping Corvette's that won't touch the gelcoat, but will remove the topcoat. You would find it at your local Auto Paint Supply store. Follow the directions exactly and as always, try a small inconspicuos spot first.

Easy off oven cleaner. Where rubber gloves and dont leave it on very long.