# Dehumidifiers



## riggy001 (Sep 25, 2018)

I am looking for a dehumidifier for a 1973 Columbia 41 Motorsailer. I want one that is self-draining and resets itself upon power loss. Any suggestions? I will put it over the galley sink to drain. Mildew is the problem. The interior space is 639 square feet.


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## danvon (Dec 10, 2012)

The cheap one that I have (about $45 on Amazon) will turn itself back on if the power goes off and then on. Might be able to just drill a hole in the plastic water trap and then stick a drain tube in. It's pretty much this one:

https://www.amazon.com/Pro-Breeze-E...dehumidifier&qid=1569211769&s=gateway&sr=8-14


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## Minnewaska (Feb 21, 2010)

The last time I bought one many years ago, it did all these things. Found it at home depot. You pulled the tray out and the interior funnel that directed condensation to the tray had a male garden hose thread.


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## wrwakefield (Nov 18, 2015)

We rely on the newer, non-compressor dehumidifier technology. We have two of these, and have heard nothing but positive feedback from others with the same model. It has all the features/capabilities you mention.

More details- including pros and cons- are available on our page about dehumidifiers.

Note: I see the models we have are currently unavailable on Amazon. [Although a boat friend just received two purchased ~2 weeks ago...]

You may be able to find it elsewhere if in a hurry... Or their model with a built-in ionizer may be just as quiet and effective... but I have no first hand experience with the ionizer model...

Cheers! Bill


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## danvon (Dec 10, 2012)

Does it freeze where you are? The type I posted the link to tend to ice over and stop working in freezing temps.


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## Minnewaska (Feb 21, 2010)

danvon said:


> Does it freeze where you are? The type I posted the link to tend to ice over and stop working in freezing temps.


I'm not familiar with any that won't freeze in low temperatures. Long before freezing air temps. The good news is that freezing air temps won't hold much moisture in the first place.

The thought of it freezing over made me wonder what the OP intends to do. Is this for when aboard or for long term storage. The later is always a fire risk.


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## danvon (Dec 10, 2012)

Minnewaska said:


> I'm not familiar with any that won't freeze in low temperatures. Long before freezing air temps. The good news is that freezing air temps won't hold much moisture in the first place.
> 
> The thought of it freezing over made me wonder what the OP intends to do. Is this for when aboard or for long term storage. The later is always a fire risk.


Fire risk is why I run a dehumidifier to try & keep the boat dry inside rather than a heater. Makes me nuts when I see boats all up and down the dock leaving electrical heaters running 24/7. I think (hope I am right?) that the low current draw and lack of a resistance heat element in a dehumidifier has to be safer.


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## Minnewaska (Feb 21, 2010)

I suspect short circuits and overheated boat or shore wiring causes most fires, not necessarily the heating element or the device itself catching fire.


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## chef2sail (Nov 27, 2007)

Canberra Gel helps with mold and mildew


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## SanderO (Jul 12, 2007)

If you have forced air heat with a well insulated (cored?) hull you'll limit humidity and condensation. I use a product I bought on Amazon which absorbs odors and moisture.

Humidity is mostly a summer problem for us as we are not on board much in the winter. In shoulder seasons we DO find moisture on alum hatch and port frames in the morning when we sleep aboard. Air however feels dry. I will check the humidity one of these days.


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## Chas H (Sep 6, 2013)

Check online for a pro breeze. I have seen them for $25+ shipping.


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## pdqaltair (Nov 14, 2008)

Many variables. 

* On the Chesapeake, spring/early summer is when dehumidifiers really help. The water can still be cold when the air is warm and humid. Ventilation only makes it worse when the water (hull) temperature is below the dew point (this is before most people put boats in the water, so they don't all know about this). Early winter can also be a problem (humid air because of the water, but cold decks). Snow on the deck is often a problem (deck colder than air during the melt). Other seasons ventilation is generally enough. But a dehumidifier is better. I've done both.
* Peltier effect dehumidifiers freeze, but it is non-damaging. If you put it on a timer, it will run at night (when it is most efficient) and defrost during the day (when the sun its the boat).


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## TimMarks (Jun 2, 2018)

Minnewaska said:


> I'm not familiar with any that won't freeze in low temperatures. Long before freezing air temps. The good news is that freezing air temps won't hold much moisture in the first place.


The self regenerating desiccant types will work down to about 30F. Compressor and pelletier types stop working below 50F or so due to freezing. I started out with a Mermaid AIr compressor type, but I have now replaced it with the EcoSeb desiccant type. The Mermaid Air is sitting on the shelf in my garage.

The dessicant type has the side benefit of putting out about 100W of heat (required as part of the self-regeneration process), which is good in the winter. I have the same type as Wakefield posted above, and it works well. It weighs about 10 lbs, so it is easy to move around and stow.

I started off just letting it drain into the bilge and the bilge pump handle it, but now I bolted a mini-condensate pump to the side of it, and let it pump overboard directly through a drain.

https://www.amazon.com/gp/product/B00KHJIC04/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Unfortunately, EcoSeb has discontinued the model I have, which has simple analog type controls, which will always restart following a power outage. Their "improved" model has electronic controls, and I suspect those won't automatically power back on.

pelletier = 0.5 pints/day (too little)
desiccant = 15 pints/day (just right)
compressor = 50-70 pints/day (more than needed on a mid sized boat)


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## pdqaltair (Nov 14, 2008)

TimMarks;2051629906... pelletier types stop working below 50F or so due to freezing....[/QUOTE said:


> Yes... and no.
> 
> They continue to build ice without damamge. Then, if you allow it to cycle off (timer) during the heat of the day (above freezing in the cabin due to solar heating) they defrost without damamge. I have done this for many years.


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## TimMarks (Jun 2, 2018)

pdqaltair said:


> Yes... and no. They continue to build ice without damamge.... I have done this for many years.


Yes, I have used those for years as well. Until I found a better way.

With the pelletier and compressor types, the amount of moisture pulled from the air slows to a trickle due to the icing-melting cycle.

But the self-regenerative desiccant types continue to chug along without any reduction in output.

Try them. You will be converted. I know I was.

Anyone want a beautiful stainless mermaid-air marine compressor type dehydrator? It is sitting on a shelf in my garage.


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## pdqaltair (Nov 14, 2008)

TimMarks said:


> ... But the self-regenerative desiccant types continue to chug along without any reduction in output....


Next time I will!


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## RichH (Jul 10, 2000)

Sweating on the inside of a hull is due to temperature diffferences on either side (inside/outside) of the hull, etc. To keep condensation at a bare minimum, simply keep a portlight / hatch etc. OPEN so that the boat will easily equilibrate vs. those temperature differences. If you tightly close a boat those thermial difference will LAG the outside temperatures ... and will enhance condensation (because you cannot seal a boat against humidity)

Mold prevention. 
1. WASH the interior of the boat with fresh water before storage - to remove any micro-salt deposition; the salt is delequescent ... meaning it attracts water. 
2. Use 3M "mildew Block" on all interior surfaces.
3. If the boat is subject to severe mold infection, spray the interior (all surfaces including 'undersurfaces' with a 'caustic' solution (I use a boat soap - Roll-Off). Spray on, wipe once to spread, let dry. The caustic surface will 'deactivate' any mold spores that attach to the surface. Not to be used on paint nor varnish.
https://www.westmarine.com/search?Ntt=amazing+roll+off

;-)


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## Minnewaska (Feb 21, 2010)

RichH said:


> Sweating on the inside of a hull is due to temperature diffferences on either side (inside/outside) of the hull, etc. To keep condensation at a bare minimum, simply keep a portlight / hatch etc. OPEN so that the boat will easily equilibrate vs. those temperature differences. If you tightly close a boat those thermial difference will LAG the outside temperatures ... and will enhance condensation (because you cannot seal a boat against humidity)


This can be true, but it's not exactly how it works. If equilibrium were all it takes, we'd never see dew outside. Leave a hatch open and you could still get serious dew inside. Ambient air temps can decline with moist air, causing dew.

Warmer air can hold more moisture before become saturated. The Dew Point is the temperature at which the current moisture level would be at 100% and any further decline will cause condensation to form. This is also why you commonly see fog when the air temp and dew point are nearly the same.

You have to come at this from one of two places, or both. First, lower the moisture in the air, so the dew point gets even lower and cold temps don't condensate. Or keep the surfaces of the boat from going below the dew point.


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## RichH (Jul 10, 2000)

As an example think about a light mass/weight trash can standing outside .... never saw one with condensation. The reason is that such quickly equilibrates the temperature and without that thermal LAG. 
regards !!!


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## Minnewaska (Feb 21, 2010)

RichH said:


> As an example think about a light mass/weight trash can standing outside .... never saw one with condensation. The reason is that such quickly equilibrates the temperature and without that thermal LAG.
> regards !!!


Then why did I have dew on both sides of the dodger glass yesterday? Yes, I've seen it on a trash can too.

Humid warm air during the day, condensates when the temps drop at night.


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## pdqaltair (Nov 14, 2008)

RichH said:


> Sweating on the inside of a hull is due to temperature differences on either side (inside/outside) of the hull, etc....


How will it equilibrate in the spring, when the water is still a chilly 50F, but the air warms to 80F? Open every hatch and the hull still runs with water, like a glass with ice in it. Spring is the time I struggle with. The rest of the year the water temperature and air temperature are closer.

This works on dry land.


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## RichH (Jul 10, 2000)

Think about the amount of condensing water if there is a great LAG of temperature during day/night. Which will have the greater 'drop out': a hull surface that is slower to thermally equilibrate or one that is 'faster' .... and knowing that which condenses MORE water will become a thermal reservoir of condensate if not fully pumped overboard ;-)


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## pdqaltair (Nov 14, 2008)

RichH said:


> Think about the amount of condensing water if there is a great LAG of temperature during day/night. Which will have the greater 'drop out': a hull surface that is slower to thermally equilibrate or one that is 'faster' .... and knowing that which condenses MORE water will become a thermal reservoir of condensate if not fully pumped overboard ;-)


I know you are a smart guy... but no. I've left my boat in the water for years, tried ventilation, and when the water is freezing and the air is warm it does not work. At all. Try to keep the condensation off a glass of ice tea with ventilation. Nope. A hull in the water, in the spring, CANNOT equilateral. The hull will stay cold. That is the point. Same with the ice tea. The condensation will stop after the last of the ice melts.


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