[satori99]

I don't have a source, but the same thing was explained to me during a sea survival course. It was a requirement to be able to enter a Sydney to Hobart yacht race.

This course included spending time in a very cold pool in full gear and attempting to activate and enter an inflatable life raft (over and over, and in the dark).

I was reasonably insulated but not in a survival suit, and I lost virtually all muscle control after about 15-20mins.

The shivers left me so weak I could barely climb the ladder out of the pool.

The instructor explained to me that this was the major point of the exercise. The right strategy is to try to minimize heat loss by bringing your knees up to your chest and not moving much (Assuming you have floatation).