I'm having a hard time wrapping my head around the topic of dehumidification on a boat. It's a given that the interior of a boat is far, far from air tight. Even if all the hatches and windows have good watertight seals, there are multiple vents to the outside atmosphere that cannot be conveniently sealed. For instance, engine room ventilation provides a huge opening into the boat from which outside air can enter the boat 24/7.
So, if one runs a dehumidifier inside the boat, and IF the interior temperature is held high enough to ensure the dehumidifier actually works, then yes, moisture is removed from the interior air, with the condensate returned to the sea. Only to be immediately replaced with moist outside air that must be heated for the dehumidifier to work effectively. Rinse and repeat.
So what is the end result? Lots of energy expended to dehumidify the outside atmosphere! And yes, I get it that responses to this topic is very very location-dependant. Those blessed with warm ambient air temps year-round probably can benefit from some form of moisture removal. However, for those of us that routinely heat our boats in the winter, either to prevent freezing or simply for comfort, seem to have limited options to keep the interior dry.
Both in SoCal, and here in the PNW, it has been my experience that maintaining the inside air temperature above the dew point, combined with continual air exchange via vents and fans, and leaving the boat with the interior opened up (i.e.-cabinet and interior doors propped open) as much as possible minimizes issues associated with moisture. Dehumidification seems like a fruitless undertaking to me.
Regards,
Pete