That boat by Yrvind was supposed to break a record by cirumnavigating the south pole many times in succession. Could hardly be called a boat, looked more like a sphere to me. I think his plan was to sail dead downwind in the storms around the southpole, which he said was most commonly in one direction... Anyway he never made that trip. At his age, he probably wouldn't have come out alive. But anyway, that's why he needed such thick insulation in the boat, by sailing in the southern oceans without any heat source in the boat except himself.

People don't sail in the winter here. It's not very enjoyable. And when the sheets freeze stuck in the pulleys its not safe.

With warm clothes and a sleeping bag, cold summer days are not an issue. But many people do have a diesel heater (or electric when connected to the grid) for comfort, which is plenty enough.