It was a full moon and the ship was VERY close to shore. Seeing (and hearing) the shore would not have been a problem. And for any healthy swimmer, neither would swimming to it have been. The problem would have been getting out of the rooms and to a location on the ship which would have allowed reasonable access to the sea, or swimming while injured or elderly.
Okay. I wonder about being able to locate the island by hearing, though, as I am sure there was lots of yelling going on.
What a scene it must have been. I hope I never have to go through such an experience.