Re: boat paint.
have you tried wetsanding until you're down past the oxidized gelcoat? it's not unusual to be able to bring it back with some careful wetsanding with something like 320 and then progressively finer up to 1500, buff it out with good compound or preferably aquabuff 2000 and finish up with 3m finesse it 2.
On painting with imron. the primary bad actor is hexamethylene dissocyanate. you CAN protect your lungs using a good combination particulate and organic vapor cartridge (the 3m one is the only one that didn't pass any through) AND IF you can avoid the temptation to use it more than once before discarding and replacing. That does not protect your eyes, skin, etc, etc, etc... and especially not in a clkosed poor ventilation garage. The biggest hazard issue is that by the time you smell the stuff, you're already in trouble
All of that being said, I don't see whay if you're determined that you bcan't roll and tip with slow catalyst and cool temps... I know thta por15's glisten clear works great and flows out after being brused on even.. it's based on fairly similar isocyanate chemistry and is probably even more resistant to damage underwater...
no matter what you paint with prep / degrease it until you're doubly sure your done and then do it again... I've had good luck with por15's cleaning products (etchants for use before laying two part isocyanate-based urethanes down).