I almost didn't post this because I'm not sure it helps the discussion.

Some of the research I have read about cold water hypothermia indicates that leaving the boat and swimming to shore accelerates heat loss much faster than you think is possible.

There have been instances when individuals did not survive swimming 50 yards from a swamped boat to shore in calm conditions, on still water, wearing pfds. They didn't drown. Their hearts stopped from cold blood temperatures.

What I haven't found yet is how to handle these situations. There may not be a solution, which makes risk assessment and management much more essential in marginal conditions. The first survival requirement is smart decision making.

Pete