If you take a Safety
at Sea course this is what they always pound into you...that you'll die of drowning from incapacitation due to cold long before you die of actual hypothermia, with the drumbeat of "Wear a PDF" always in the background. But then again, that's in the background throughout the entire seminar.
The fact is that if you fall overboard
with the boat
sailing downwind in any appreciable sea state it can easily take more than an hour for the boat
to stop, turn around, get back to where they think you fell in and then find you...if they can find you. In six foot seas your little head
is visible for maybe 2 seconds out of every 10...and that's with someone looking right where you are. Every 30 seconds that passes before the fact that there is a MOB
is realized essentially lops a big chunk off your chances of survival unless you're wearing a PDF.