I have AC on the boat, but it's 110-AC powered, which means you stay tied to the dock in order to run it. The boat cools down to about 72-degrees in less than an hour, and that's when it's in the mid 90s outside. Because of the balsa core, which is fairly thick, the boat tends to remain fairly cool for several hours. Also, the white topsides of the boat tend to remain fairly cool, even in direct sunlight.
I see a lot of boats out on the bay with dark blue hulls, and I often wonder just how hot they must be inside the cabin when that late afternoon sun is blazing down on the hull.