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Old 22-11-2015, 14:02   #16

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No need to put a radiator under your berth. There are electric mattress warmers, sold to the RV and trucking industry mainly. Same as an electric blanket, but built specifically to go UNDER your mattress (or mattress topper) and warm it from below. Nice and toasty, just make sure you have the battery power for it.
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Old 22-11-2015, 19:25   #17
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Even in Florida you can have that issue in winter as the boat is warmer that the water. We had a major issue the first year until we read about using the drideck. I can tell you it works really well. No problems since then.

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Old 22-11-2015, 19:42   #18
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We've used Hypervent for a few years and live aboard in humid and sometimes cold environments. It works. It is crucial to maintain air access to the material, so no quilts draped over the side of the berth. Our berth has full access to one side and limited access on the other three.

Here is a link to Defender:

Hypervent Condensation Prevention Matting
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Old 22-11-2015, 20:14   #19
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An old thread but always topical.
We solved most of the mattress moisture problem by having a memory foam topper pad which has closed cells and keeps body vapour from penetrating the mattress. - Comfy too.
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Old 23-11-2015, 12:09   #20
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Re: Mattresses Moisture Argh!

This is great stuff. Have used it on two boats, but it is pricey. It is VERY stiff so keeps its loft even with a very heavy person. Not sure if it is available everywhere.

HyperVent 39-50 | Fisheries Supply
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Old 23-11-2015, 12:13   #21
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Re: Mattresses Moisture Argh!

I just moved my hot water tank in the compartment under the bunk . There's enough heat escaping that to keep the area warm .

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Old 23-11-2015, 19:51   #22
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Re: Mattresses Moisture Argh!

Originally Posted by swami maximus View Post
I was wondering if anyone has some good homemade suggestions for dealing with mattress moisture. I have searched these forums but cant seem to find anything that specifically address this issue. A lot of talk about it, but not much on what to do with it. I was thinking of either taking the mattress out and drying it thoroughly, then covering it with a plastic of sorts to prevent penetrating moisture. OR... getting a bunch of milk crates and cutting them apart to form a grid and then using thick mesh to keep my foam from filling the small squares of the grid. Bunk, grid, mesh, mattress... Sound good or does anyone have a better idea?
I've been using Hypervent [as others have mentioned] or similar products for 30+ years living aboard in latitudes 56N-62N. I always run it up the sides and ends of the mattress as well. It breathes whether covered with blankets or not...

I also have been making my own fleece bedrolls [the size of the mattress] for this long as well. Much warmer and easier to 'make the bed'...

If you want something higher tech, look into the Froli system.

If you perform a 'Google custom search' on this forum you will find lots of other discussions about this topic...

Dry the mattress soon before you have mold and mildew to deal with...


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Old 21-12-2017, 18:25   #23
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Re: Mattresses Moisture Argh!

We're liveaboards. The nights can get pretty cold, and like most boats (and RVs), we don't have much insulation. We do have shore power though, and with shore power comes an (a drum roll please)...


Oh glorious warm berth... After shivering in the salon (I exaggerate), we go into the aft cabin and slide into the pre-warmed bed and skoosh down into warm blissful sleep.

Only one problem. The blanket keeps the warm air trapped against our skin. That's its job. So where does the humidity and air actually go? Down into the mattress. And, if the mattress is resting on the cold fiberglass, it condenses into water and BANG. The cabin starts smelling like a dank mildewy basement.

We went with Den-Dry mattress underlay. It lifts our mattress about three quarters of an inch above the fiberglass, and lets the air move freely, carrying the humidity away before it can condense, and what little does condense on the fiberglass evaporates easily, because it's not soaking into the mattress. Once we put it down, no more problems. It's kind of like hypervent, but it's stronger, has channels for better venting and most important, it's cheaper.
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Old 30-12-2017, 16:25   #24
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Re: Mattresses Moisture Argh!

I got the foil covered bubble wrap and put it under my mattress and lapped it up onto the hull. This got rid of much of the moisture but not all of it. To controll the rest I flip the mattress up and allow it to air dry during the day. It's -7 F up here in Maine tonight. A wet mattress is no longer an issue.
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Old 30-12-2017, 16:43   #25
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Re: Mattresses Moisture Argh!


Here's a thread you might be interested in:

It is about a new product.

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Old 06-01-2018, 02:10   #26
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Re: Mattresses Moisture Argh!

We've been sort of struggling with this issue ourselves. We moved out to the main cabin for a while, but decided to try insulating the vberth. We laid one or one and a half inch thick rigid closed cell insulation on the hull beneath the vberth, up behind the fiberglass liner, and behind the wood 'bulkheads' concealing the anchor locker section of the bow. We were able to fit the rigid foam tightly together, and already the moisture and chill back there has diminished. We have a few more things to finish, and the last bit of rigid foam to place, but we are ready to try (ulp!) cutting down our new-to-us memory foam mattress.

Currently in the cabin, the mattress is protected from moisture and gross stuff with a zippered waterproof protector. (I sprinkled borax in there on general principles, fyi). We still get the plush feeling with a plush topper.

I am totally going to use HelloSailor's info (post #9). Previously, I had used astroturf, which works, but not in December and January--just too much moisture condensing on the uninsulated hull surface.
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Old 06-01-2018, 04:57   #27
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Re: Mattresses Moisture Argh!

Under my mattresses I had laths of hardwood sitting in grooves cut in battens--so there was a s[pace under the laths and mattress was held clear of the plywood decking.

Now all yo need do is to have a cross flow of air under the laths--and this is easily achieved by drilling the battens with small holes at intervals--and taking the air out vis ahole let iointo the last batten which has no other holes. A small solar panel and battery driving a smallexpelair type fan. They are quite cheap--computers use them--and you do not have to do anything but let it ex[pel into the cabin.

The inlet to the space under the mattress can be rigged so that the air passes through a dessicator--but that would be getting too elaborate. Mine never gave any trouble just sucking fresh air through.
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Old 06-01-2018, 07:09   #28

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Re: Mattresses Moisture Argh!

Increase ventilation in the sleeping space.

In cool weather, increase dry heating temperature after getting up each day.

In hot weather, blast the aircon.

Originally Posted by swami maximus View Post
getting a bunch of milk crates and cutting them apart to form a grid
Greenhouse benching material works well 2'x4', ensure empty space below.

Or try these first

Anything that gets air circulating under the mat helps.
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Old 06-01-2018, 08:13   #29
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Mattresses Moisture Argh!

If you can’t put the water heater under the bunk, excellent idea by the way, never thought of it myself.
Then give a Froli a good look, expensive, but it does work. This year since we moved aboard I went and spent a whole lot of money on a custom Marine innerspring mattress and sold the Froli. I’m thinking now maybe I shouldn’t have. Manufacturer told me it wasn’t needed though.
Now that the weather is in the 20’s here in Georgia we are getting condensation in the boat, leaving a hatch open all the time helps greatly, runs up the electric bill of course, but we are now getting a wet mattress where the mattress lays against the exterior hull.
Two days ago I put a Yoga mat against the exterior hull between it and the mattress. It seems to help greatly.
Only cure I see is to head South, but ventilation, dry heat and insulation all seem to help
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Old 17-01-2018, 03:42   #30
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Re: Mattresses Moisture Argh!

Well it's that time of year again. What hasn't been mentioned is a simple heating pad. They come in various sizes so depending on your electrical ability..... I have found that in colder weather my refrigerator doesn't run very often so I have that electricity to use in the heating pad. Also if the heating pad is under the mattress once it heats up it doesn't need nearly as much electricity to keep it hot as it did to warm up.PS I owned a 12 volt electric blanket but it used way too much electricity and did nothing to remove the dampness from the mattress. (I'm at anchor and get all my electricity through solar and wind)
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