| Interesting to read that Scandinavian boaters do not discuss insulation. The Swedish boat builder/sailor/adventurer Sven Yrvind https://en.wikipedia.org/wiki/Sven_Yrvind designed a boat with if my memory is correct about 10 cm thick foam walls and he made sure to have the window frames catch most of the condensation which I guess he handled with some kind of gutter as planned.

I have to agree with H.W. about windows. Use acrylic, double pane, or both. I have lived in environs way colder than one would see at sea, and only very old windows get condensation.

Perhaps small human occupied spaces spike the humidity much higher, making condensation a thing I would not see coming.
That seems kind of dangerous, as mold seems not far behind. Makes a glass epoxy interior more attractive. Would not want wood, or anything else that feeds mold.

Has anyone discussed/considered an air to air heat exchanger for living spaces? It would seem a light, low energy fix for warm and cold climates. Common residential units would work, I think.

It's one thing to live on a boat in very cold climates. How is it to sail? The combination of cold breeze and wet spray seems deadly.

Additionally, do heat pumps make sense for heating/cooling? They can have a coefficient of performance of 4-6 (one watt in, 4-6 watts of heat/cooling out) and, they work both ways. For cooling it makes sense. Not sure if the source water is 0c it works for heat. Perhaps a water jacket on a heat source (gas/wood/diesel heater) would work well.

Do any of these idea also work for warm climates?
Do boats have warm climate AC? Or dehumidifier needs?

Does one drop a water feed hose into the water for a watermaker/whatever? Or does a HOLE IN THE HULL, which seems a big Rob do not want, seem a good idea?

Figuring this stuff all out seems more complicated than the original boat design.