Back in my collage days, my parents owned a place up in New Hampshire. My dad had built a summer cottage on a hillside with a gorgeous view of Mount Washington (the tallest peak in the Northeast). After taking up skiing, I went up there during the winter breaks to hit some of the slopes just 15 minutes away. As a summer cottage, it was not well insulated. The strategic purchase of a quality sleeping bag made the stay tolerable. On one trip, we found out that gasoline will not evaporate below -45 degrees (F). How did we determine this? It was -45 degrees and the cars would not start. Once the sun came up a little higher in the sky the temps soared to a sweltering 20 below.
After surviving these winter trips, the sleeping bag has stayed with me for years. It has came in very handy. One weekend, I decided to stay on board, and the temp outside dropped to around 20 degrees. A few other crew members had east jump also decided to stay the night, and seemed to be more affected by the cold. Keep in mind that a boats fiberglass hull does not have much insulation. If you’re planning on staying on a boat overnight, make sure you have the proper gear for the task.
The same can be said about keeping warm underwater. A quality wetsuit or drysuit / undergarment will keep you warm! This past weekend I was diving in 38 degree water for over an hour. I was comfortable the whole time. Other divers were complaining of about the cold. If you purchase the proper gear, and maintain the gear properly, it should keep you warm, and last for years.