Kristian,

If the boat went too deep it would eventually implode on itself and the men would problably know nothing about it, they'd die instantly. However the human body is almost all water so it would not be crushed by the actual pressure, but they'd be crushed and ripped to pieces by the implosion of combined water and metal.
Divers have been working at over 305m (1,000ft) from bells.

Nice subject

Cheers Ron