Deep sea divers

Paddy and Murphy are havin' a pint in the pub, when some scuba divers come on the TV. Paddy says, "Murphy, why is it them deep sea divers always sit on the side of the boat with them air tanks on their backs, and fall backwards out of the boat?" Murphy thinks for a minute then says, "Paddy that's easy. It's 'cos if they fell forwards, they'd still be in the damn boat!"