I'm going to guess that it's a catalyzed (2-part) linear polyurethane
....they get pretty darn rock hard when they cure, much harder than epoxy.
Although if it were epoxy, what you could be seeing is cloudiness from UV
damage rather than oxidation. Either way, all you can do is sand it as far
as I know. Neither will strip off with anything that I've heard of. If you
sand it aggressively enough to smooth the top layer (light-touch 80-grit or
100-120 grit), then primer with a high-build primer like Interlux Barrier
Kote 404/414, then paint ...it'll look like a new boat.

Brian


"Gordon" wrote in message
...
I just rescued an old O'day 20 and decided to clean up the oxidized
looking hull. That's when I realized the boat had been painted and I
wasn't
trying to clean gelcoat.
Apparently it is epoxy and is HARD. So. how do I clean it up? Wet sand?
Heavy duty rubbing compound doesn't touch it!
Thanks
Gordon