Re: Dark Gelcoat Boat Hull UV Protection
I would give Aerospace 303 a try. I've had amazing results with it on boat hulls & sun surfaces (both light & dark colors). Where I live the boating season is all year long and the sun is relentless. SPF 40 means something on a black hull.
A sample of it and other products can be ordered from their site. If you like then order some from AG. The surface must be prepped first, true of any product you apply.
Rick in Deep South Texas