I agree about the hazards of swimming in cold water. Remember that the ship was not in danger of sinking;it was grounded. Jumping into the water would not have been a smart move.

I have done some scuba diving in 36 degree water. I have vivid memories of suiting up in an insulated drysuit. Just before we got in the water, boiling hot water was poured into our gloves which we then donned, plunging into the water immediately. The dive was over when our hands got so cold we could no longer take notes or sketch - typically about 40 minutes. Cold water is not trivial.