Probably out of print now, but worth reading if you can find a copy.

Puzzled why some people died quickly when shipwrecked yet others survive quite long times he concludes that the will to live is key. He then goes on to develop survival strategies & proves them by increasingly long voyages on an inflatable, ending up by crossing the Atlantic in a rubber duck without food or water!

Excellent book, lots of useful stuff about drinking sea water (it is possible) and getting fluids from fish caught etc. But most of all, survival is about the will to live.