gelcoat

[unclejack3]

Sorry to sound stupid but if i mix epoxy resin with hardener is that not called Gelcoat? Because the more I sand this boat the more interesting the boat becomes in revealing it's past. So I am thinking of why not just put an epoxy clear coat encapsulating the whole hull..
Anyway I know what you are thinking...

 

[Indysailor]

Others with more expertise will surely provide details, but generally epoxy should be considered structural and adhesive, so that when combined with fiberglass mat, it holds things together to form the deck, hull, etc. But it's not UV resistant. Gelcoat, on the other hand, is a decorative finish that can be colored, polished nice and shiny. But it doesn't have the same structural capacity.

 

[Davidasailor26]

Gelcoat and epoxy are two different compounds. Gelcoat is polyester based; epoxy is, well, epoxy based. They each have slightly different properties. For your case the big differences are:
- Epoxy will stick to either other epoxy or polyester substrates. Gelcoat can stick to both, but getting it to stick to an epoxy substrate is a little finickier. Unfortunately neither is really guaranteed to stick well if the lower layer is paint.
- Gelcoat is reasonably UV stable, but epoxy generally isn’t. If left exposed to the sun without a UV stable coating it will discolor and may turn brittle.
- Epoxy is generally considered fully waterproof. Gelcoat is very water resistant but can allow some osmosis over time when submerged.

In a case like yours I would probably not bother with gelcoat. I would sand as much as necessary to get remove whatever layers of paint are there. I’d put an epoxy barrier coat on the bottom and then some type of anti fouling, maybe VC-17, on that. Above the waterline I’d use a paint, probably a quality two part paint like Alexseal, with their primer underneath. If the surface isn’t smooth I’d fair it with an epoxy based fairing compound first.