I guess it depends on at dock
or at anchor
? Basically you have to worry about moisture build up in the boat, not necessary it being too cold. The best way is to keep one small port open in each hull and then the top hatch
cracked in the saloon. That will provide enough ventilation that you won't be dripping in the morning. You'll want plenty of insulation
underneath bridgedeck type births, the difference in temp between the air under the boat and the inside is extreme, so I'd recommend 4" of closed cell insulation
, dry deck panels
, and then your mattress. The reason for so much is your trying to stop temperature differential condensation
, and it's most extreme under your bridgedeck mattresses. Trust me, the constant dripping and waking up with all of your clothes and bedding moldy after 1 day will kill your trip far faster than simply being cold.
Then you'll want a powerful source of heat in each hull, webasto furnaces are the best. Heat only travels up, so the settee area will benefit for the hull based heaters but having something like a propane
furnace up in the settee area will do absolutely nothing for your living space down in the hulls, so plan your heat to be placed down below. Webasto furnaces are very small, put out nice dry heat and are extremely powerful. One place down in one end of each hull and blasting its heat forward will be enough to keep that hull and the settee area above nice an toasty. Surprisingly it doesn't really need to be put through ventilation ducts, just have the one vent from the webasto shoot from your fore or aft cabin
straight down through the hull.