I know I won't last long even in water off Florida in Winter without some kind of thermal protection.

At 6' 170lbs I am lacking in enough fat that even in indoor swimming pools while working as a Dive Master I needed to wear a wet suit top. On open ocean dives off of Fort Lauderdale in winter I would wear a full 1/4" farmer john with a 1/4" top (usually unzipped at least a little) and be very comfortable while others were in 1/8" shorties or no wet suit at all, other divers would look at me like I was crazy and going to over heat but after a 45min. dive I could still be quite chilled.

Once while diving to cleaning the bottom I stopped to replace a zinc ater being in the water about 30 min. Got the old one off but couldn't put the new one on, I was shaking too much. I was alone so got out of the water but just barely and I was in the full 1/4" suit described above on a mooring off Stuart, FL.

Haven't done any underwater boat work alone since, lesson learned!