Join Date: Jun 2006
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I have a 12,000 BTU Mermaid Marine Air A/C-heat pump system that is very nice indeed, but which needs a hell of an amperage kick to start and won't work when the water is less than 40 F. There may be a way to run in when on the hook, but I'm not there in my thinking yet.
The idea is to create a single warm "room" in which a bulkhead diesel heater will run. It might be possible to use the existing vents to send warm air to other parts of the boat this way, but that's not the prime rationale, which is simply to take the edge off the cold in marginal conditions. Even this week, with haulout approaching, the unheated boat is still 15-17 C, which is light sweater or fleece temperature.
The saloon and the aft cabin are capable of having water-tight doors installed (yes, I would have proper venting to avoid poisoning or suffocating ourselves). This would make the saloon a smaller space to heat, and there is enough room to sleep in there.
There is a great deal of closed cell foam and sprayed insulation to the waterline. If it weren't for the greenhouse-like pilothouse, which is frequently 12 C hotter in summer than the saloon or the aft cabin, the boat is warmer and drier naturally aspirated, so to speak, than a lot of F/G boats of my acquaintance, which tend to condense expelled breath. I've been "rained on" in my bunk in spring and fall aboard space-heater equipped F/G boats...it's unpleasant.
A lesser-acknowledged benefit of a bulkhead heater is the ability to exchange the air several times a day and to dry out the boat thereby. Even when it is not strictly necessary to heat the boat, sometimes it would make sense to have the diesel heater on low to help retard mildew and condensation.