Let me quote the advice that is given to anyone operating around the coast of Great Britain by the Coast Guard & by the Royal Navy. Which is: IF YOU DON'T GET OUT OF THE WATER BLOODY QUICK, YOU ARE DEAD!! Survival time in the water is anything between 2 mins & 30 mins. Incapacity in half that time. Wear a proper survival suit and get yourself a double bottomed raft. If you do die, no raft & no suit might mean no money from your insurers. Great place to leave your Missus and kids.