The Watch Below by James White

"Somehow they had to find a way... Doc Radford, the Exec, Wallis, and First Officer Dickson, together with two badly injured and hysterical nurses. They were stuck. In the pitch dark, bleak cold of a hull equipped with oxygen tanks and stored food. And nothing else. Under several fathoms of water. Somehow hey had to find a way to stay sane long enough to make a new home. And billions of miles out in space there were aliens- water breathers whose own world was gone forever in gusts of titanic heat. They too had to find a way- a way to survive for generations, long enough to find a new home. Aliens and humans alike had the same problem. This is how they met it."--Back cover.