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Old 11-11-2014, 12:09   #16
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

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Originally Posted by giant View Post
Thanks also Thinwater for answering the 12 volt dehumidifier question... Anyone using one?
I've been running one for 3 years. I actually run it in 110v so that I can use a timer. But it is the same unit with an adapter.
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Old 11-11-2014, 13:43   #17
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

I bought an Ausclimate compact dehumidifier and use it in my tri, best thing I have ever bought for the boat, no more mould and boat is crisp when I open her up. I can put all wet sails, ropes, cushions, wet weather gear, PFD's etc down below, turn it on where all the water drains into the sink drain and close up the boat.!! It really is fantastic for our climate.
P.S. I live in central Queensland, Oz so high humidity, inside boat normally at 80+% but with the dehumid it pulls it back to 47%.
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Old 11-11-2014, 13:59   #18
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

Thanks again Thinwater

Will definitely use a dehumidifier when I get my boat and the 12volt\240volt (Oz) option is probably be best for me as likekly mostly be on a moring or anchored, not in the marina.

Lowering humidity inside the boat will restrict both mold and corrosion (wiring\electronics\engine) etc. Saving maintenance\money\health etc.

A low draw fan to circulate air would also be a plus.

Of course just having a hatch or two venting or one of those solar powered deck fans may be enough depending on circumstances.


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Old 11-11-2014, 14:45   #19
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Thumbs up Re: Dehumidifier efficiency in keeping the boat reasonably dry

We use a Meaco DD8L, which always keeps our 43' cat nice and dry all year round. As mentioned by others it is important to prevent air exchange with the outdoor. The unit operate on 230V and draw from 150 W to maximum 600W.
It control the humidity automatically according to your setting. On full power it will dry wet clothes in a head if the door is closed.

think it was voted best buy in Yachting Montly in 2013.

best of luck in keeping your boat nice and dry.

Happy lead fre sailing
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Old 21-01-2015, 18:00   #20
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

I'm in a climate that is cool and humid year round. Controlling cabin humidity in my case is merely a matter of keeping the cabin temperature at 15 degrees F above ambient to achieve 60% maximum humidity. A 20 degree F ratio will achieve 50% humidity.

If I used a heater and set the temperature at say 70 degrees F, that setting would only be effective when the ambient temperature was below 55 degrees (at 100% ambient humidity). And on cool drier days, I would waste money by unnecessarily heating the cabin. And as the ambient temperature dropped at night, I would waste more energy by maintaining the same temperature in the cabin.

So I instead installed a Honeywell humidistat (cost $35) that turns on a simple oil-filled heater (cost $40) with the thermostat set to turn it off at 75 degrees F. The humidistat is set at 60% humidity. I save a lot of money on power this way because at night, when both the temperature and dew point drop, I can allow the cabin temperature to drop to follow the dew point down and don't waste energy trying to maintain a constant temperature in the cabin (I don't care about comfort when I'm not there). So this approach is a "constant humidity" rather than "constant temperature" approach. During the days, when it's sometimes dry, the heater doesn't run at all.

It's important to use a heater that does not have a fancy electronic temperature controller because the controller will lose its setting when the humidistat switches off its power. Also, the humidistat is only rated at 7.5 amps (900 watts at 120 volts), so a heater drawing more than that will overload the humidistat.

I use an oil-filled heater because its surface doesn't get hot enough to ignite anything. Its surface tops out at 250 degrees measured by my IR thermometer.

Of course, I use the same heater when I'm on board and set it for comfort instead of controlling humidity when I'm there.

Attached is telemetry from my boat's cabin taken over a week. You can see the "sawtooth" pattern in the temperature, which is the humidistat switching on and off. You can also see how the ratio between the dew point and temperature remain constant (except for some "free" heating on a dry day), while the temperature is allowed to vary with ambient. The ambient humidity during this week was 100% for about 8 hours each day.

I believe this is the cheapest and most energy-efficient approach, at least for my cold/wet conditions. It is cheaper to add heat (provided you have some ventilation) - than it is to run a dehumidifier's compressor to extract the water.

I don't like the idea of sealing the cabin from outdoor airflow and running a dehumidifier because it just encourages mold spoors to stick around and grow.
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Old 21-01-2015, 18:22   #21
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

We live on our 44 steel cc every other week. When it gets well below freezing we get ice on the aluminum hatch frames, which then rains on us. Sometimes we get some condensation from the overhead even though it is insulated.

I got a dehumidifier, found it needs to be over 60F to work, so that bashed putting it in the aft cabin. But it won't drive the humidity down much below 50%. So it doesny do much for us.

9F a couple of weeks ago. We were comfy, but we do get some condensation.
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Old 29-01-2015, 18:14   #22
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

P.S. Fan driven space heaters make me very nervous. If the fan fails - which it's apt to do quickly in a salt air environment - the heater may fail catastrophically, i.e., melt down and start a fire. I suggest sticking to oil-filled convection heaters for boats.
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Old 06-06-2015, 08:19   #23
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

Hi Petar,
So I see your post and wonder what did you do to keep the moisture out and the air moving. I live here on orcas Island and have a Back Cove 30 that I am pondering the same question to keep mildew and corrosion to a minimum. Thanks for your reply and experience.
Jeff Johnson
Coastal Dane
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Old 06-06-2015, 08:30   #24
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Re: Dehumidifier efficiency in keeping the boat reasonably dry

The Evadry unit I mentioned in my earlier post (also search my blog) does NOT have a lower temperature cut-off like compressor units. Efficiency does drop off--there is less water in the air and the coil does freeze--but it is not damaged and continues to operate. I run mine year round into single digit temps. I think it is 5 years now.

In the winter I run it night-only. Often the boat interior will get above freezing in the sun, which gives it a chance to defrost.
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