In my nonscientific opinion, I would say that the wood of the ship would begin to warp, at bare minimum. I guess I figure it's the extreme version of what humidity will do to doors in old houses.
As far as the breathability of the air, I agree that the crew would begin to take damage from the superheated oxygen. It'd be wet, hot, and hard to breathe. Depending on how close they were to the exposed, boiling sea, the insides of their lungs would begin to scald, I would think, and they might have to see if they're affected by some semblence of heat stroke.
Now, in game terms, I'm not sure how it'd play out, but I'd categorize it as a Very Bad Situation. Fortitude saves to halve damage, fortitude saves to remain concious; I'd reckon the ship's joints and seams would begin to crack and swell.
Just some thoughts.