If you were on a cruise liner ship in the night in the middle of the atlantic, & it overturned, sinking?

Modern cruise ships has self-detatching self-deploying life rafts for such an incident. Next time you're on a real cruise ship look for those white barel-like canasters next to the big orange life boats. Chances are, some of those would be on the surface. As far as swimming, anyone can tell you that the salt solution in sea water will help keep you boyant without you expending too much energy on your own (that's why scuba divers wear dive belts). If the ship merley capsized, and didn't go under, I'd try to get people coordinated to make an joined effort to get ontop of the belly of the ship (now facing up) and get out of the water.