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  #31  
Old 11-06-2012
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Re: Winter Moisture Control

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Originally Posted by miatapaul View Post
..... it was less than $50 for a 10.5 inch by 20 foot (Crobra brand by GAF).
Is that really a whole lot cheaper? say $40 for a 10.5 inch by 20 foot chunk.. pretty much the same as $10 for a foot that's 5 feet wide.
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  #32  
Old 11-06-2012
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Re: Winter Moisture Control

Defender.com Search Results: hypervent $10/foot x 40 inches at Defender, and yes, it's worth it.

We lined the entire inside of the boat with Reflectix one winter. The esthetic was funky but it was warm!
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Old 11-06-2012
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Re: Winter Moisture Control

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Originally Posted by wingNwing View Post
Defender.com Search Results: hypervent $10/foot x 40 inches at Defender, and yes, it's worth it.

We lined the entire inside of the boat with Reflectix one winter. The esthetic was funky but it was warm!
Yes, it does start looking a bit like the lunar lander!
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  #34  
Old 11-06-2012
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Re: Winter Moisture Control

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Originally Posted by Jgbrown View Post
...Oil heater is going out, and I'm putting the dehumidifier back in. Much better :-)

Still uncertain on the whole dehumidify and venting at the same time(seems counterproductive to do a lot of both.
The trouble with heating is that it solves the problem in the heated area; the water simply builds to higher levels and then moves to cooler areas (forward under the bunk or in lockers against the hull) where it can condense. Obviously heat does not remove water, it only makes it more soluable in air. It is only truly effective if you heat enough, consistantly, to keep everything above the dew point.

Dehumidifying and venting... why? But you knew that.

The only problem with dehuidifying alone is that at very low temperatures (below about 50F) dehumidifiers lose effectiveness. While there may be enough water in the air to cause dew or frost, there really isn't enough for the unit to catch on to. Then some heat can help.
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  #35  
Old 11-06-2012
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Re: Winter Moisture Control

Good insulation and a good woodstove eliminates both problems.
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Re: Winter Moisture Control

I find this thread interesting. Usually condensation is a result of the space temperature being below the dew point. Insulation doesn't stop heat loss, it only slows it down.

My concern with installing insulation or hypervent on the outboard side of the hull is has anyone removed the product after a winter of living aboard to see what's growing behind it? When we first started building tight energy effiicent homes, we discovered that the moisture within the house eventually lead to mold problems because the houses were so tight, they did not exfiltrate. This issue was solved by the installation of heat recovery ventilators which moved that mositure to the outdoors.

In my mind a boat does not breath or exfiltrate. Ventilation really is the key to removing moisture inside a boat that creates all these problems.
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  #37  
Old 11-07-2012
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Quote:
Originally Posted by pdqaltair View Post
The trouble with heating is that it solves the problem in the heated area; the water simply builds to higher levels and then moves to cooler areas (forward under the bunk or in lockers against the hull) where it can condense. Obviously heat does not remove water, it only makes it more soluable in air. It is only truly effective if you heat enough, consistantly, to keep everything above the dew point.

Dehumidifying and venting... why? But you knew that.

The only problem with dehuidifying alone is that at very low temperatures (below about 50F) dehumidifiers lose effectiveness. While there may be enough water in the air to cause dew or frost, there really isn't enough for the unit to catch on to. Then some heat can help.

For me heating is about getting moisture into the air so it will exit the boat via one of the vents.


That's exactly my puzzle with it, people do recommend both. The mold under my mattress has certainty caused me some stress. Tonight I threw the full power dehumidifier in there, already down to 40 %.


To other poster: it really does help, I was really worried about what I'd find behind the insulation panels(loose fit reflectix). My boat was the poster child for potential mold issues at the time, badly ventilated, no insulation, propane heated. The only place without mold was the areas behind the insulation, hull was clean there. As I understand it, if the insulation slows heat loss enough that the inner surface of the insulation is above the dew point, you don't get condensation. This proves out nicely with my v berth, the part that molded was the only part right above cold air in a uninsulated locker. They had taped all the way around the edge of the reflectix, the one edge they forgot had some mold behind it.


EDIT: What about http://www.homedepot.ca/product/cobr...version/967450
instead of hypervent? Seems fairly similar, and available locally.

Does anyone know of a source for hypervent in Canada?

http://www.advancedbuildingproducts....watairvent.cfm
looks to be exactly the same as hypervent but I can't find any source for it.





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Last edited by Jgbrown; 11-07-2012 at 03:30 AM.
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  #38  
Old 11-07-2012
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Re: Winter Moisture Control

I've never really been tempted to live aboard over the winter in cold weather. Looking forward to it down south one day. However, there are moments where we've thought about it.

There are two problems with moisture. First, the amount of water vapor available and the dew point, which will determine whether it remains in the air.

On a boat, it is nearly impossible to keep water from being evaporated into the air. Boiling water, showers, wet bilges, breathing, etc, etc. You will add moisture to the air, there is no stopping that.

The dew point is more complicated. It is expressed as a temperature, but is really a factor of ambient temperature and how much moisture has been evaporated into the surrounding air. The more moisture in the air, the higher the dew point will be, meaning the closer to the ambient temperature it will be. Said differently, it is the temperature at which the air would no longer be able to hold onto the amount of moisture absorbed within it. The warmer the air the more moisture it can hold. 70 degree air can hold more than 50 degree air, which can hold more than 30 degree air, which can hold more than 10 degree air, etc, etc. Reduce the temperature and there is a point where it can no longer hold the moisture within it and it condensates out.

The biggest problem with a boat in the winter, is not keeping the interior air above the dew point, its keeping the hull above the dew point. While you may keep the salon table relatively warm, put your hand on the hull inside a hanging locker or galley cabinet. It will be much colder, maybe by tens of degrees and undoubtedly below the dew point. That's why you get condensation, followed by mildew, and not necessarily where you can see it. Insulation helps, but as some have pointed out, it may only transfer the problem behind the insulation if the moist air can get behind the insulation.

The only good solution, IMO, is to substantially reduce the actual humidity in the air, thereby, reducing the dew point below even the cold hull temperature. That can only be done effectively with electric powered dehumidifiers IMHO.
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Last edited by Minnewaska; 11-07-2012 at 06:54 AM.
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  #39  
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Re: Winter Moisture Control

>The only good solution, IMO, is to substantially reduce the actual humidity in the air, >thereby, reducing the dew point below even the cold hull temperature. That can only >be done effectively with electric powered dehumidifiers IMHO.


That works if you're tied to dock w/ shore power. The reality is you want your heating system to be capable of producing suffient air changes per hour within the boat to get rid of the moisture. It's all about pressure.

A perfect example are the diesel fired heaters like espar. You can set these up so they heat 100% outside air or recirculate the return air. Recirculating the air is more energy efficient. If you're recirculating 100% of the return air, you should consider taking in a small percentage of outside air on the return side. In doing so you pressurize the inside of your boat. By keeping a hatch cracked open you get the air changes per hour necessary to remove the moisture.

In Brent's example of using a wood stove, air is needed for combustion. Although it's under negative pressure due to the process of combsution, the air changes per hour are occuring naturally, thus removing the moisture. Plus wood produces a dry heat.

Considering the couple of examples above, it all's about ventilation.
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Re: Winter Moisture Control

Quote:
Originally Posted by misfits View Post
>The only good solution, IMO, is to substantially reduce the actual humidity in the air, >thereby, reducing the dew point below even the cold hull temperature. That can only >be done effectively with electric powered dehumidifiers IMHO.


That works if you're tied to dock w/ shore power. The reality is you want your heating system to be capable of producing suffient air changes per hour within the boat to get rid of the moisture. It's all about pressure.

A perfect example are the diesel fired heaters like espar. You can set these up so they heat 100% outside air or recirculate the return air. Recirculating the air is more energy efficient. If you're recirculating 100% of the return air, you should consider taking in a small percentage of outside air on the return side. In doing so you pressurize the inside of your boat. By keeping a hatch cracked open you get the air changes per hour necessary to remove the moisture.

In Brent's example of using a wood stove, air is needed for combustion. Although it's under negative pressure due to the process of combsution, the air changes per hour are occuring naturally, thus removing the moisture. Plus wood produces a dry heat.

Considering the couple of examples above, it all's about ventilation.

The ventilation is where the hypervent comes in(or similar product) allowing those air changes to pull the moisture out from under the mattress . However, I think that insulation makes a huge difference too, as in the example of hull temperature, if the insulation keeps the surface temperature 10-15 degrees warmer(and based on my floor vs before insulating the surface, it does) that can certainly help to prevent the condensation forming in the first place.
As a secondary benefit, if it means that the air in the boat stays warmer until it is exhausted from the boat it would mean it holds more moisture.

The hyperdry in lockers at least is less about insulating, it just prevents things from touching the hull and giving that dead air space for mold to form. I've used it in my lazarette and it's making a big difference in how wet things stay(the hatch leaks badly).
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