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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 10-09-2008
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How dry is too dry?

This is not a question about martinis!

We recently began using a home-style dehumidifier on our boat (moored at a slip with available power) and so far are impressed with how the boat is dry, and the residual waste heat from the unit is keeping the cabin spaces nicely warm so far. I know we have to maintain a minimum temperature to avoid freeze up, so that may be an issue later when things cool down some more.

We are running it in constant mode - not to an RH setpoint. It is filling the 30 pint reservoir in 3-5 days. I will rig the constant drain into a sink but wanted to monitor the moisture removal rate for a while. Our less-than-guaranteed-accurate humidity gauge is showing approx 30%RH after two weeks of this.

Anyone think there's a danger of getting the interior too dry running it constantly? Seems unlikely especially here where it's going to be raining a fair bit over the winter and the humidity is locally generally pretty high..
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Faster..Portugal is a very dry country, we have our boats in real dry conditions and nothing happens..

Mositure is an enemy..dry, is not...you should be OK...I think the drier the better

Side note...I know a guy installed an electric de-humidifier in his boat, and it ate away all his zincs and caused a lot of galvanic corrosion

Alex
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Old 10-09-2008
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If you are going to use a de-humidifier (that collects water); I would think you want to keep the vent ports closed. Otherwise you won't decrease the humidity in the boat very much relative to the outside air. On another note; when I leave the ports open to allow ventilation the oiled teak tends to dry out very quickly where the ports are open. I don't know if a warmer interior during the day would be worse on all of the teak but if you can keep the humidity at or a little above 30% that should be good.

Sounds like your friends 110V system is grounded to the engine (12V) ground Giu. A 110V device in itself should not cause a galvanic problem; but of course I could be wrong.
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We're 220V in Europe..

He had the boat all the time connected to shore power..and has 220V, directly from the shore connection to a plug in the salon.. inside the boat...even has a galvanic isolator...

We never figured it out..but were able to conclude it was the de-humidifier, as in the summer, no use for it, the zincs last normal..
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In buildings 40-50% rh is often considered to be the ideal range. Over 60% mold can grow and conditions that are too dry can help support dust mites and other allergens. 30% is low but I do not believe it is in the too dry range from a air quality standpoint.

You sure won't be allowing any mold or mildew to form unless you have surfaces where condensation forms - such as in lockers adjacent to the heated parts of the boat.
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Comfort levels aren't really the issue here.. when we're aboard the de-hi will be off, and the RH levels will be ambient until we leave the boat again. My (slight) concern was with things like drying out wood work that may shrink and open joints.. but in retrospect at 30% we're probably still OK

Keeping mold & mildew away, and cushions dry is the object here.

Thanks all.
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30% will be fine for the boat. under 30% you can start drying out the the woodwork. even at 40% you would be safe as far as mold & mildew are concerned.
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Old 10-10-2008
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Faster- when you get the boat to 30% RH, would you let me know? I want to move into it as I'm getting a little moldy and mildewy myself lately. Thanks, I knew you would understand.

John
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Old 10-10-2008
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I'm no mechanical engineer, but it sounds like your de-humidifier can't dry things out much less than 30% RH no matter how hard it tries.

As water is taken out of the air, past a certain point it takes more energy to take more water out then the thing can deliver, so at or around 30% RH, the thing will run happily but not do anything (no drips from the outlet).

Barring other electrical problems (corrosion, fire, etc.) you should be fine. I'd be more concerned with overheating if you're runing it constantly and it happens to be too big for the cabin space.

The manual "should" give you a minimum room volume and minimum RH (assuming it's not made in Asia).

Cameron
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I recently saw a boat for sale that included two units kinda like this:



It was the driest boat I've ever seen, no musty smell, the bilge was spotless and looked like it'd never seen a drop of water in 23 years. Now that I've seen the apparent results, I wonder why everyone with shore power doesn't use one.
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