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Old 06-04-2020, 07:38   #46
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Smile Re: Condensation And Smell Under Mattress

We lived aboard for many years, at times also in very cold climates. We were frozen in a few times with ice thick enough to stand on all around the boat.

Your body gives off a considerable amount of moisture when you sleep. What happens is when this moisture comes in contact with any cold surface, such as what the mattress is sitting on, this cold surface will cause the moisture to condense onto the surface. The mattress sitting on top, insulates the base it sits on enough to ensure the base stays cold enough to cause the moisture to condense.

You can see why many of the suggestions others have made might work. It depends on how cold the climate is that you are in, as to how far you have to go to solve the problem. Anything you do to create air circulation under the mattress will help to raise the temperature under the buck, which will help you avoid the condensing. It will also help to remove the most air exchanging it with the air in the cabin which will have lower humidity. In cold climates the air in the cabin should already be pretty low in humidity, unless you're heating with something like a Force 10 propane cabin heater, which is marginally vented. Propane gives off lots of moisture when you burn it.

So, ventilating, or adding some kind of air space, or putting insulation onto the surface of the bunk, like armaflex, can also help, however, if it's cold enough outside, you may find this is not enough to completely solve the problem.

What we did was to add a heating element. We used restive wire, meant to be used on 12V, that came from the agricultural industry. This is used to heat seed beds. We made loops about 12" apart running back and forth under the mattress. It drew about 2- 3 amps for our queen size bed, if I remember. We were on a dock with AC, so this was not a consideration. You may be able to do the same thing by buying a 12V heating pad. I think they sell these for the RV market. Anything that raises the temperature enough so that the base is above the condensation temperature will completely solve the problem. Doing this means you don't have to worry about the bedding, such as your comforter, blocking airflow. It won't matter, since the base is above the temperature which would cause condensation.

On another note, Amaflex can be used on hard surfaces like your hull sides to prevent condensation. Most boats have no insulation. When you live aboard in cold climates, many things like hull sides, metal hatches and more, will be cold enough even to condense moisture. It's a common problem. All of these issued can be solved, but since boats are not generally used in cold climates, builders don't see the need.

Good luck
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Old 06-04-2020, 07:48   #47
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Re: Condensation And Smell Under Mattress

If you are getting a pool of condensate under the mattress, you need to get rid of the moisture, as you are already keeping your mattress away from it with the slats. For a Boston winter live aboard, I used a couple of mini dehumidifiers (had to empty every day usually) along with the dollar store moisture eliminators (they charge about 5 or 6 times that price at the hardware and marina stores) distributed in various locations on the boat (these lasted a couple of weeks or so, before having to replace them).
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Old 06-04-2020, 07:54   #48
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Re: Condensation And Smell Under Mattress

If you cannot get airflow, then you just cannot stop the condensation; sometimes you just can't get a fan underneath. In those cases you have to accept the moisture (that you will need to clear occasionally) but somehow stop it moulding and smelling.
I eventually started using a mattress underlay on some of my bulkhead cushions as I could not get airflow behind them. I found one with a silver impregnated spacer that seems to stop the mould and smells even if you can't stop the moisture.
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Old 06-04-2020, 08:04   #49
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Re: Condensation And Smell Under Mattress

We used common wooden bed slats, spaced about two feet apart. Easy to cut them for a perfect fit, helpful with odd shaped mattresses on some boats. Cannot feel them at all. They are inexpensive and do a great job. No problems since installing them. note* we put strips of felt, evenly placed, on the bottom of each slat to prevent rubbing/squeaking.
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Old 06-04-2020, 08:05   #50
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Re: Condensation And Smell Under Mattress

Originally Posted by scarlet View Post
I've been staying on my boat for the last 10 days, and the weather has been cold.. anywhere from 30's to 60's.

2 days ago, I started smelling a really bad smell in the master cabin. Thought it was the head. Didn't really smell anything in there, but went ahead and pumped out, rinsed, and added KO.. smelled like a lovely spring garden..

The smell in the cabin didn't go away. I checked the bilge, and it was clean and dry, and I couldn't smell anything coming from there. As I moved towards the berth, I started smelling it really bad. In fact, it was so bad, I could barely sleep. So, yesterday morning, I tore apart the berth. I have 3 compartments under my berth. 1. a completely empty large drawer, 2. the compartment for the air conditioning, 3. the diesel tank. couldn't isolate any smell, but I didn't see any water, mold, mildew, etc. completely clean

There was, however, water from condensation under the mattress, on the wood base. I have slats under the mattress that lifts the mattress approx. 2"... Mattress was dry, but the wood seemed saturated, and, there was standing water of about 1/4 cup distributed about under the berth. I believe that's where the stench was coming with. I cleaned the entire area with a mold and mildew cleaner... dried it as much as I could with towels, then put my electric heater in the cabin, closed it off, and ran the heater all day to dry the wood out. it does smell a little better.

I am expecting that there will be more condensation tomorrow, and I figure I will need to take the berth apart, and heat up the cabin to dry out the wood.

So, my question is... what can I do to stop this? Do I need higher slats? Do I have no other choice but to tear it apart and dry it every day? I use the electric heater at night, so, it is pretty dry in there. Enough that I wake up with dry mouth, and dried lips. Any suggestions?

(I have a 2011 Lagoon 450, in beautiful shape, clean as a whistle)
There are products like I think itís called Folio or something close to it that raise the mattress and allow air to flow stopping the mold and mildew. Do it quickly. Once that get into the mattress youíre done.
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Old 06-04-2020, 08:08   #51
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Re: Condensation And Smell Under Mattress

I have used this device called ďGolden RodĒ which is a low power heated tube that I placed in our closet. It should work well under a mattress.

Available from Amazon.
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Old 06-04-2020, 08:21   #52
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Re: Condensation And Smell Under Mattress

Originally Posted by Zanshin View Post
I'm a huge fan of Froli mattress springs. Not only do they give necessary ventilation under the mattress, but they can transform a simple boat-type cushion into what feels like a real bed mattress.
Scarlet, I want to big for Froli. My wife and I have tried all the other solutions on two different cruising boats....looking for something to stop that condensation. It wasn't until we bit the bullet and bought a Froli kit that it all went away. I tried it on one quarter berth, and was converted in one night. I told my wife that there was no more moisture AND no back pain from crappy boat pads. She tried it, and said "I'll come back to our double berth as soon as you order more of this stuff. Until then, find somewhere you like sleeping."

Needless to say I ordered more immediately. ;-) We've moved on to another boat, but all the Froli came with us and we've been sleeping dry and comfy for 15 years.
Dan Leach
s/v Endless Song, Anacortes, WA
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Old 06-04-2020, 08:23   #53
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Re: Condensation And Smell Under Mattress

Is there ventilation in the space under the mattress ? There should be. Otherwise, just stand the mattress up when you get out of bed.
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Old 06-04-2020, 09:11   #54
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Re: Condensation And Smell Under Mattress

Hi, we had this problem with the wing bunks in our trimaran. I put Dri-Dek under all bunks and it worked for me.
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Old 06-04-2020, 09:13   #55
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Re: Condensation And Smell Under Mattress

Originally Posted by Zanshin View Post
Canarios - I disagree with your statement about a dehumidifier being a requirement to reduce humidity. I suspect that the 99% of boats that don't have a (power hungry) dehumidifier aboard would agree with me.

The way to reduce the humidity is to ventilate - that brings the humidity below the mattress down to ambient humidity.
You are wright, however Iím talking about reducing humidity as soon as and aleays when you can connect to landpower. For the moment Iím at Gran Canaria with the boat. High humidity. My home harbour is Stockholm where its cold but not sobhigh humidity. Two different places. Two different ways of handling the problems.
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Old 06-04-2020, 09:58   #56
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Re: Condensation And Smell Under Mattress

We simply put a layer of builder's syrofoam sheets directly under the mattress. No more condensation since then, as the insulation prevents the bottom of the mattress from getting cold. We used the 3/4inch, as that is what we could get, but any thickness will do the job. And the pieces fit together nicely, as they have a step built in for just that purpose.

So, instead of condensing on the bottom of the mattress, the moisture from our bodies just escapes from the top and sides of the mattress instead.

Problem solved
Noel Swanson

Life is too short to live in ugly places.
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Old 06-04-2020, 10:22   #57
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Re: Condensation And Smell Under Mattress

I have a box of Frolis that I am not using as we don't often overnight on the boat. Sufficient for a double.Froli Mattress Springs for Boats & RVs - $175 (Edgewater, MD)

model name / number: Travel kits 28322 & 28324

Froli Travel Sleep System for boats or RV mattresses. Kit is adaptable to any shape of mattress or cabin and provides ventilation as well as support. Kit contains 46 firm, 14 soft & 12 edge spring elements to cover about 22 sq ft. Also contains 12 tension clips & 72 base elements. Gets great reviews and costs over $350 at Defender and other stores.

Can ship them to you if you want to make an offer and they should solve the problem and improve the mattress support.
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Old 06-04-2020, 10:39   #58
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Re: Condensation And Smell Under Mattress

Lots of good ideas. I just put closed cell "memoryfoam" topper-pad over the mattress so no moisture could transfer from bodies to matress. Hot and sweaty some nights but very comfy and dry mattress under.
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Old 06-04-2020, 11:58   #59
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Re: Condensation And Smell Under Mattress

We had a similar problem on our trawler and resolved it by putting a layer of "dimpled" plastic beneath the mattress. It is the product used on the outside of foundations to conduct moisture away and is a plastic sheet with approx. 1/4" dimples throughout to allow for air circulation.
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Old 06-04-2020, 12:29   #60
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Re: Condensation And Smell Under Mattress

We cut a pattern of ten 6" diameter holes in the plywood below the mattress to provide ventilation. Worked fine but YMMV depending on what is under the bunk.
Ann-Marie Foster
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