The "Rule of 50":
An average adult person has a 50/50 chance of surviving a 50-yard swim in 50-degree F water.

I don't know how accurate this is but I've seen it repeated by several sources over the years. I think the only prudent thing to do is to invest in a wetsuit (at a minimum). It's just not worth the risk. Live to sail another day!

Sail safe,
Todd