We figured this out years ago in the North Sea. We all had survival suits. It is basically insulated waterproof coveralls with flotation and boots. It will keep you alive until rescued. You can put it on in a minute or less. If you go into the North Sea without this you lifespan is maybe 30 minutes in the summer about 5 minutes in the winter.
Cold water kills. You loose function of limbs and go to sleep and drown. It is actually painless but you are still dead.
“It will keep you alive until rescued”
depending if you are with in a specific time fram