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Old 29-11-2010, 17:02   #16
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If you're talking about condensation under a mattress, that's a whole 'nother matter. Zeehag mentions Dri-Dek tiles, and we've found them to be useful despite being ridiculously expensive.

Curiously, I've found every boat I've owned to have a wet-under-mattress cabin. On the present boat, the forward cabin has no problem, but the starboard aft cabin needs the Dri-Dek. On the previous boat, the aft cabin was no problem, but the forward cabin needed Dri-Dek.

A great mystery.
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Old 29-11-2010, 18:02   #17
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I live on a wooden boat with a 1" thich hull, 2" thick ribs and a solid ceiling inside of that (open at top and bottom for ventilation) so don't have much in the way of condensation. The worst place I found was under the mattress where I slept, until I put a Mylar survival blanket under the mattress with the Mylar facing up, this reflected my body heat back up (temperature difference is what causes the condensation).
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Old 29-11-2010, 18:14   #18
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Dew point

Any boat will have condensation if the dew point is reached on any interior surface or item. To prevent the air from reaching the dew point on a surface the surface must be warm enough so that water does not form.

I have used a Soleusair dehumidifier for several years now with no condensation. If you have shore power I highly recommend this unit. It has modern switch-mode electronics so that the power factor is unity when it operates.
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Old 29-11-2010, 18:23   #19
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Quote:
Originally Posted by Island Mike View Post
We generally find more condensation during the colder months on our sailboat. It is worst when we are anchored out, boat gets cold during the night, we light the fireplace or stove during the day and it causes condensation. In the summer it may get humid and sticky, but generally not condensation..
I live on board and as the marina where I live is replacing my dock I am spending the winter on the hard, I am getting more water in the bilge with the boat out of the water than with it in (winter air temp around the boat is colder than summer water temp).
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Old 29-11-2010, 19:22   #20
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I lived aboard for a winter in Norfolk on my Morgan 35. Had two electric heaters that were always cranked to the max and still not overly warm in the boat. Every surface on the boat was constantly coated with moisture. So much condensation collected in the low points that I thought I had major deck leaks. Turned out it was just condensation in a big way. Norfolk is a high humidity area so that partially counts for the collected moisture. Really needed a vented heater to draw that moist air outside.
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Old 29-11-2010, 20:13   #21
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Condensation seems to be a problem that is alot more prevalent in fiberglass than wood boats.
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Old 29-11-2010, 23:39   #22
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I had the same problem as roverhi. Single skin glass boat, no outside cover, in the water at temperatures going as low as -20C. My biggest expense that winter was paper towels. Every surface was wet, all the time. With two people aboard, and cooking on an alcohol stove, it was terrible. My electric heaters ran full blast from the time I go home in the morning after working all night til I went back to work. Insulation is vital to keep the inside surfaces warmer. Next time I try this I'm using a steel boat with 2 inch foam insulation, a cockpit cover and the deck will be covered with Fiberglas batting under shrink wrap. I may even do the hull sides the same way. And I'll be using diesel or kerosene heating which is vented, with the ports open so good airflow happens.

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Old 30-11-2010, 00:20   #23
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I'm curious about those of you who have solved the under the mattress moisture problem. I know its condensation, and we've reduced it some with insulating the hull and a 1/2 " layer of closed cell foam under the mattress, but not solved. Does the Dri-dek work? It makes sense that there would need to be air flow under the mattress. Tips?
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Old 30-11-2010, 07:59   #24
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We use "HyperVent" from Defender - looks like a tangle of spagetti but makes for good air flow, far better than the dry-deck stuff because its made to channel air. Lived aboard 8 winters in the Chesapeake with this and no problems. Lined some lockers where condensation could be an issue with Reflectix from a hardware store (the stuff that looks like silver-sided bubble wrap) and run a dehumidifier when we're at the dock.

We're an inch thick solid fiberglass hull and solid fiberglass without a headliner above. One particularly bad winter, we taped Reflectix to every surface above the waterline. The appearance was funky, a bit like having a mirrored ceiling, but it did improve the heating efficiency. It also had a nice mold layer underneath when we took it down in the spring.

Agree with the suggestions about not making pasta when you're in for 3 days of rain ... but at the same time, when its going to be cold and dreary, I crave a pot of bean soup. Must be in my genetic coding LOL!
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Old 30-11-2010, 19:33   #25
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So your vote to prevent condensation;

1, insulation?
2, ventilation?
3, heating?

also I am having my cousins cover redone, the vendor insisted for the extra $16 per cousin...that he instal on both side 1in of the same material they put on mattreses...its a humidity supresor...he claims that this in combination to regular turnover my cousins will keep dry as bones...you can see this matterial at anny matteres shop, they always have a half cut demo for costomers view.
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Old 30-11-2010, 21:44   #26
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Has to be 1 and 2. Insulation is the key, look at a double glazed window, 90% of the time, no condensation but a single glazed window will mist over very quickly. That's down to the air barrier in the double glazed window providing insulation.

My present boat is make of wood and I NEVER get condensation as wood is a good insulator. I have a de-humidifier in the master cabin but other than that its just ventilation and a bit of heating.
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Old 01-12-2010, 12:24   #27
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The right answer for us is 3 and 2...sort of. By increasing the air temp of your boat, the relative humidity drops. Wikipedia "Relative Humidity" puts the principle well:

"A useful rule of thumb is that the maximum absolute humidity doubles for every 20 F or 10 C increase in temperature. Thus, the relative humidity will drop by a factor of 2 for each 20 F or 10 C increase in temperature, assuming conservation of absolute moisture. For example, in the range of normal temperatures, air at 70 F or 20 C and 50% relative humidity will become saturated if cooled to 50F or 10 C, its dewpoint and 40 F or 5 C air at 80% relative humidity warmed to 70 F or 20 C will have a relative humidity of only 29% and feel dry. By comparison, a relative humidity between 40% and 60% is considered healthy and comfortable in comfort controlled environments (ASHRAE Standard 55 - see thermal comfort)."

Blah Blah Blah- All you need to remember is a warmer boat is a drier boat. Bonus points for keeping surfaces and not just air warm (which is largely what insulation helps with.)

The other issue - ventilation, really translates into removing the additional moisture in a closed system (our boat) that we add through breathing, cooking, bathing, etc. So the solution really isn't ventilation per se, but dehumidifying the air by bringing in drier air than what is inside your boat. Ventilation can remove lots of moisture in the air, but using a dehumidifier also works to accomplish the same thing. However, ventilation also has an advantage of circulating air into "dead spots" that may have lower temps than the main cabin, higher humidity, or both.

For example: We keep the door closed and open hatches to the bath after taking a shower. After 5-10 minutes, all the water is out of the air since we intentionally dropped the temp well below the dew point. Then we use a squeegie, shower pump it over the side, and close hatches to warm the space back up. As the air temp increases, the relative himidity drops back down...

So the key to having a warm dry boat is to keep your boat warm and dry.

(Nice and dry inside my "plastic" boat...)

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Old 01-12-2010, 13:12   #28
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I would contest that a bit, ever been in car on cold damp day/night? The surfaces that have no insulation, like windows and exposed metalwork, will have a lot of condensation on them even though the car's heater is on and you're nice and warm. By the same token, there is reasonable airflow as the car's heater is a fan pumping air in, which then exits through vents, usualy in the boot (trunk for you US of A'ers) or rear pillers.

It's all very well saying that keeping the interior warm will help, and it will, but if you don't have adiquate insulation you're asking for condensation and more importantly, wasting a lot of energy as well.

I really can't see anyone in a cruising boat wanting to have the heating on full time because the hatches are open, bleeding the heat out off the boat.
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Old 01-12-2010, 13:37   #29
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Quote:
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I would contest that a bit, ever been in car on cold damp day/night? The surfaces that have no insulation, like windows and exposed metalwork, will have a lot of condensation on them even though the car's heater is on and you're nice and warm. By the same token, there is reasonable airflow as the car's heater is a fan pumping air in, which then exits through vents, usualy in the boot (trunk for you US of A'ers) or rear pillers.

It's all very well saying that keeping the interior warm will help, and it will, but if you don't have adiquate insulation you're asking for condensation and more importantly, wasting a lot of energy as well.

I really can't see anyone in a cruising boat wanting to have the heating on full time because the hatches are open, bleeding the heat out off the boat.
That's because the surfaces aren't yet warm, the cold windows have a lower dew point than the warmer air, like Rick said above. Then again, I can't remember a time being toasty in a car with condensation on the inside of the windows unless some very heavy breathing was going on, adding more moisture...

I don't disagree with insulation's importance on helping energy usage, but if you have a closed system (your boat), and you add moisture through breathing, cooking, bathing, etc., you have to have a way to take the moisture in the air out- either through ventilation, dehudmidifers, or (like us) a combination of both.



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Old 01-12-2010, 15:33   #30
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..... unless some very heavy breathing was going on, adding more moisture...

Frank
Ah, that could be my problem!

Seriously, fair point, however, my point is that with proper insulation it takes much LESS heating to keep everything warm and dry. The car's windscreen will clear because warm air is blown on to it to warm it up and dry it, the side windows, especially in the rear where the heating is less, will take ages to clear, if at all. A car like an S class Merc' with double glazing doesn't have this problem because the windows are better insulated.

To sum up then, I just wanted to disagree with GeoPowers as he discounted insulation as a major factor. IMHO, it's just as important as the other two. It's not the be all and end all of the problem, you still need a decent amount of the other two to remain dry and comfortable.
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