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Rockstar2011 06-04-2011 09:39 PM

Damp cabin
I have had my boat for a week now and I have noticed that the cabin tends to get damp at times. The magazine I have in my magazine rack is wilting due to exposure to moisture. I slept on the boat the other night and felt damp myself (no, I didn't wet the bed ;o) ) When I lay my sleeping bag out, it wasn't even out for that long, maybe a couple hours, and it was damp when I went to get into it.

This doesn't seem normal. Just wondering what you guys think.

tempest 06-04-2011 09:56 PM

Did you leave ports or hatches open when you slept on the boat?
Do you have any fans..going?

Is there water in your bilge?

Rockstar2011 06-04-2011 10:09 PM

Nothing left open. There is a solar vent that is always on. No water in bilge at all.

SlowButSteady 06-04-2011 10:09 PM

Ventilation ... ventilation ... ventilation

CalebD 06-04-2011 10:15 PM

One solar vent (that may not be working at night) going while I'm sleeping on any boat would not do it for me. You need ventilation, period.

tomperanteau 06-04-2011 11:44 PM


Originally Posted by SlowButSteady (Post 737306)
Ventilation ... ventilation ... ventilation

Can't be stressed enough. I have started on planning for small fans along the inside of the hull in places where they can suck air out of the boat. Mean time I have things opened up and always have a light on that can produce enough heat to circulate air flow. A constant flow is necessary if you want to keep the moisture and the smells down.

SlowButSteady 06-05-2011 12:17 AM


Originally Posted by SlowButSteady (Post 737306)
Ventilation ... ventilation ... ventilation

Some more specific points:

- You should have at least one vent, powered or not, for each compartment; even if air can flow freely between the compartments. My 27' boat has a cowled vent forward, a solar exhaust vent in the head (mid-ships), and a louvered companionway hatch board.

- Moist air is less dense than dry air, so you will usually have warm, moist air high in the cabin. A solar exhaust vent at or near the highest point in the cabin will therefore be most effective at getting moisture out.

- Arranging your boat's vents so that air flows along the length of each compartment (or even the length of the entire cabin) will help to dry out moist surfaces, cushions, fabrics, et cetera. Small circulation fans will help tremendously in this respect, but take electrical power.

- Two or three people inside a small enclosed space (e.g., a boat cabin) can generate a lot of warm, moist, air (even if everyone is behaving themselves ;) ).

allene222 06-05-2011 01:20 AM

I went through this a few months ago on my boat and studied the issue to death. I wrote it up (kind of a free from blog) with lots of little humidity calculators if you are interested Humidity. The bottom line is that if you seal something up, it will go to 100% humidity. If you keep it open, you can keep it to the humidity of the outside. To do better than that, you need some kind of smart vents that let dry air in and moist air out (nobody does that on a boat) or an electric dehumidifier (air conditioner like contraption). The little bags you buy that fill with water help very little. Everyone is right, ventilation is the key. As an example, my cockpit lazarette cover was always dripping water when I opened it and everything in it was always wet. Since I started leaving it cracked 1 inch, it is always dry. My article has some hints on getting an accurate hydrometer cheap and a few other things but like has been said, it comes down to vents. I run a low grade heater with a fan not to heat the place but to facilitate air circulation.

DonScribner 06-05-2011 06:42 AM


Are you sailing during the day? Is it raining at all? I don't know about your boat, but mine is a somewhere between an elegant, beautiful elderly woman and a fat old bag. The POs maintained some things and not others. The last PO was nice enough but had NO BUSINESS being on the water in anything, let alone a sailboat. Just saying. So, one of the items not maintained is the toe rail. I have to pull them both up, reseal the deck joint and rebed the rail. As it is, the carpet is always damp and often outright wet. Maybe you have a nuisance leak like that.

TakeFive 06-05-2011 09:34 AM

Some contrarian thinking
Ventilation will only get your air as dry as the exterior air. I don't know what evenings are like up in Toronto, but around here they're HUMID. All that moisture captured by the day's heat cools at night, and it practically condenses on your skin when you go outside. That's exactly what you'll get as your reward for cutting a bunch of holes in your boat to increase ventilation. I did NOT want that happening inside my boat.

I took the opposite view. Seal 'er up real tight and suck the moisture out. It's worked great for me, and the boat is dry as a bone every time I go there. Fortunately I have shore power to keep a dehumidifier running 24/7. It draws about 60w:

Another source of condensation may be the cold water up in Toronto. If the inside of your hull is below the dew point of the air (another reason to dehumidify), you could get condensation anywhere below the waterline - settee lockers, V-berth, bilge, etc. Increasing ventilation to these areas might evaporate the condensation, but it could also INCREASE it. Think about it: You're constantly providing a fresh source of humid air to the cold surfaces below the water line. OTOH, insulating those areas could prevent the condensation from occurring. If you can insulate them well enough, LESS ventilation might actually be better.:

About 80% of the people here will disagree with me on both of these things. Many of them are far more experinced sailors than I am. So take this contrarian thinking with a grain of salt. But my concepts are based on good science and engineering, so they're worth considering.

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