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Old 14-06-2020, 01:43   #1
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Best bedding material.

Howdy, I live on anchor on my 37-foot Fiber Glass cat.
There is never any water in the bilges, ever. But I have damp bedding and cushion covers. I'm on the East Coast of Queensland Australia.
I know it is just from the high moisture content of the air and am wondering if some materials are better than others to stop this happening.
I have noticed that edges/corners of fixed cushions seem to absorb more moister than does the center of the cushion.
Thanks for any comments or advice you can give.
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Old 14-06-2020, 04:09   #2
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Re: Best bedding material.

The most comfortable material is the heavy,heavy foam.

If a 48 inch wide mattress is hard to lift it will do fine sleeping on the usual slab of plywood.

The moisture comes from somewhere , frequently the bilge is damp , or the hull will sweat. .
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Old 14-06-2020, 05:18   #3
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Re: Best bedding material.

Two routes to solving the problem have been aired (ouch) on the forum. One is inserting a breathing space below the cushions/mattresses using gratings of some sort. The other is reducing the moisture in the air in the boat. Heating helps if you are in a chilly environment, even at the level of leaving a lightbulb turned on. We went the route of a small dehumidifier that discharges into a sink, and are happy with that.
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Old 14-06-2020, 06:19   #4
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Re: Best bedding material.

I have slept on a boat virtually every night for 20 years. Most of that time in cool, damp San Francisco. I do understand this problem. Water under a mattress on a boat is a very common problem, and there is a lot of misunderstanding about the source and best cures. But it CAN be completely eliminated with a bit of a scientific understanding of what’s happening.

The water does not come from the bilge, or even from the damp air. It comes from YOU. At night you sweat, the resulting water evaporates off your hot body (that’s NOT a judgement amount your looks!) and moves as water vapor down through the mattress until it gets to a place cold enough to condense, usually the wood, or FRP shelf the mattress sits on. Just about the WORST case is if you have a manufactured mattress with a vinyl layer on the bottom. Now the water accumulates INSIDE the mattress... Yuck! You can’t stop sweating, so this process is inevitable.

Over time lots of water can accumulate here. Enough to rot wood, blister fiberglass, and make life smelly and miserable for people onboard.

The solutions come in two flavors. You can try to increase air circulation below the mattress so the water that collects can evaporate during the day and disappear. There are many ways that have been sold to do this, basically creating an air gap under the mattress. I have found them to be marginally effective, especially for a full time live aboard boat where the bed is used every night, and in cold climates. Helpful, but not a fix.

Better, is to avoid the problem in the first place. For a berth that is a full time bed, a waterproof mattress pad (NOT a “breathable” one!) will stop the migration of the water vapor down through the mattress. Lots of variations of these are available—usually sold to people with continuance issues. The water, not finding anyplace cold enough to condense, will move up through the sheets and blankets and leave into the cabin air (unless you sleep with a rubber top sheet... but that’s s special kink).

For a berth than is used as a seat and not covered with bedding all day, you can actually disassemble the foam pad from the fabric cover and wrap the foam in very thin plastic (disposable painter’s drop cloths work great!). You’ll never know it is there, and it makes a great vapor barrier.

If you can get a vapor barrier between you and the bottom of the mattress, you will fix virtually all this problem.
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Old 14-06-2020, 06:45   #5
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Re: Best bedding material.

I have found that doing exactly the opposite also solves the problem.

Get a plain yoga mat (ours are about 1 inch thick, 2 ft wide) and place it just below the bunk mattres.

It is odd you get this challenge in Queensland. We only ever get this in Sweden / RSA Cape Town / NZ, etc. - cold waters and high moisture in the air. Never in hot climates.

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