Bottom of Mattress Wet!

No I did not pee in the bed.

As livaboards we found a livaboard issue the other day. Condensation on the bottom of our mattress. It is made of high density foam. We got everything cleaned up and asking how can we prevent this?

A friend of ours is telling us that there is a kit (?) to put under the mattress that creates an air cavity between the mattress and the bed frame. True? If so where can I get one?

The water condenses at the freezing point .

A few solutions work , some sort of pad (think super sizes scotch brite pad) that will allow warm cabin air under works fine.

So does drilling the bed and allowing more cabin heater air under the bed.

What works is basically any method you can work to have the bottom of the mattress stay above freezing.

Some times simply lifting/airing the mattress daily will get rid of enough moisture that it wont ice at night.

It's called HyperVent. I've used it for years and it really does work. Sold at Fisheries Supply for $10/ft. (39Wx3/4" thick).

Yup- good stuff!

I tried hypervent but it didn't solve the problem. The center of the mattress still got wet and mildewed.

So I bought the Froli Sleep System (Froli Sleep Systems by Nickle Atlantic, LLC). The bed is more comfortable AND the bottom of the mattress stays totally dry. More expensive than hyper vent, but more effective too.

The old hypervent is in good condition and still in the back of my car, so if anyone wants it and can pick it up, let me know! Free to a good home...

We sold the Froli system for a couple of years before we went cruising. It's the best. The only place you can get it now is from Nickle Atlantic. The woman you deal with is a little cranky but you will get an awesome product.

We use HyperVent under our main berth. Solved the problem perfectly and is still doing so some 16 years later.

FF said:

The water condenses at the freezing point .

A few solutions work , some sort of pad (think super sizes scotch brite pad) that will allow warm cabin air under works fine.

So does drilling the bed and allowing more cabin heater air under the bed.

What works is basically any method you can work to have the bottom of the mattress stay above freezing.

Some times simply lifting/airing the mattress daily will get rid of enough moisture that it wont ice at night.

Click to expand...

Condensation occurs at dew point.

boatpoker said:

Condensation occurs at dew point.

Click to expand...

That's what I thought, the saturation point depends on the temp/humidity

We get a lot of dew (condensation) here in Florida way above the freezing point like the mid 60's and up. No ice scrapers needed just wipers.

Fog forms well above freezing and it is complete condensation (super saturation)

I went to the home improvement store and got several pieces of roof ridge vents. They are usually about 1" thick by 12"x 48". You can drill a few extra holes in each panel.

Something like this: Air Vent: Hip Ridge Vent

A lot cheaper than $10 per sq ft and work great.

Condensation occurs at the dew point

SCOTTEDAVIS said:

That's what I thought, the saturation point depends on the temp/humidity

We get a lot of dew (condensation) here in Florida way above the freezing point like the mid 60's and up. No ice scrapers needed just wipers.

Fog forms well above freezing and it is complete condensation (super saturation)

Click to expand...

Don't mean to be picky... just trying to straighten out some technical terms that are sometimes confusing.

Condensation forms at what is known as the DEW POINT (YES - this is also saturation point for that temp - super saturation is something else again and probably outside the scope of this conversation).
Dew point is a function of the moisture content in the air - otherwise know as ABSOLUTE HUMIDITY LEVEL...
Not to be confused w/ RELATIVE HUMIDITY which as a combination of how much water is present (ABSOLUTE HUMIDITY) and the AIR TEMP (which affects how much moisture the air can hold at that (and only that) temp.
So - relative Hum changes as the air temp changes - absolute Hum (and Dew Pt) for practical purposes does not change w/ temp.

When the air cools to the dew point you get saturation & condensation.

The above - and a whole lot more - is covered in the US Power Squadron Weather Course - which is now available online as well as live through local Sail & Power Squadrons. See USPS.ORG if interested.

Bacchus said:

Don't mean to be picky... just trying to straighten out some technical terms that are sometimes confusing.

Condensation forms at what is known as the DEW POINT (YES - this is also saturation point for that temp - super saturation is something else again and probably outside the scope of this conversation).
Dew point is a function of the moisture content in the air - otherwise know as ABSOLUTE HUMIDITY LEVEL...
Not to be confused w/ RELATIVE HUMIDITY which as a combination of how much water is present (ABSOLUTE HUMIDITY) and the AIR TEMP (which affects how much moisture the air can hold at that (and only that) temp.
So - relative Hum changes as the air temp changes - absolute Hum (and Dew Pt) for practical purposes does not change w/ temp.

When the air cools to the dew point you get saturation & condensation.

The above - and a whole lot more - is covered in the US Power Squadron Weather Course - which is now available online as well as live through local Sail & Power Squadrons. See USPS.ORG if interested.

Click to expand...

Thanks, I have a good working knowledge about the subject from my USCG, Private Pilot, and Sky Warn Weather Reporters classes.

Dew point does indeed change with temperature, when the temperature goes below the dew point water will condense out of the air and the air will have less humidity in it. Cold air can not hold as much water vapor as warm air.

The dew point is the saturation temperature for water in air.

The dew point is associated with relative humidity (RH). High RH means that the dew point is closer to the current air temperature.

When the dew point and the air temperature are the same look out for fog. Ask any pilot when flight planning about the importance of dew point air temp. spread.

The point was water does not condense at the freezing point as was stated as a fact.

The term supersaturaion should not have been used by me as this is rare outside of a lab due to nucleation particles present in the air, cloud/fog formation will occur before supersaturation is reached. Sorry

We used the DriDeck (?) tiles sold at WM. Worked for us for six years on our sailboat.


Bob

FYI, You can also get the mesh style from Columbia Marine Exchange in PDX. We have it under our mattrest and it has kept it dry & mildew free.

So the bottom of your mattresses are freezing! I knew there was a reason i lived in the south.

Our aft cabin has a water tank under the bed. the cool water combined with out body heat makes for some condensation, so I put a layer of hard insulation across the top of the tank. It really helps a lot.

We use the Froli system and it solved the problem we had with condensation.

Living aboard in NYC the dew point was easily reached and the water produced would freeze to the unvented , unheated sail locker under the bed.

An electric sheet was not enough heat to drive the dew point out if the heavy foam mattress , but lifting to vent when un occupied did the trick.

A fitted sheet under the mattress aided in lifting with out harming the frozen foam.

When folks decide they want to liveaboard , there are many interesting challenges , this is only one.

Dri-Dek tiles worked for us... a really easy fix.

As I get older or invite the grandkids, a rubber sheet helps the mattress from getting wet

On a more serious note, we have found that heavier guests sweat a lot more when sleeping and even with the air vent stuff under the mattress, after a few days moisture can appear. Jenny Craig or Slim Fast maybe??

Froli works great in getting rid of condensation issues. As an added bonus it also acts somewhat as a box-spring under the mattress, improving comfort. Especially if you have a typical boat mattress...

Look into getting air flow out of the space below the mattress. The PO put a fan and piping system in the space under the mattress. It's called a circumvent. I've got the literature on it but cannot find a reference for it on the web. It works quite well. He also put that thick "scotch brite meshy thingy" under the mattress as well.


Jim
Sent from my iPad using Trawler Forum

Especially if you have a typical boat mattress...

Any mattress (or seat cushion ) has a hard job plopped on a slab of plywood.

Hypervent or something similar is on my list of "Things to do" -- Seaweed's insulation is nonexistent.

What I did in the bilge locker was take the 1/4" foam that came on my solar panels and placed it along the hull. That was enough for the locker under my bunk and the two under the dinette seats.

I should have done the bunk first but it was summer time then and now... well, raising the mattress, with assorted winter gear (electric blanket, etc.) is difficult.

It seems like there ought to be a non-marine source for some sort of scrubby (like hypervent) for lots less money.

janice142 said:

It seems like there ought to be a non-marine source for some sort of scrubby (like hypervent) for lots less money.

Click to expand...

Tuff-N-Nuff Rock Shield by Greenstreak protects pipelines

I have no idea of cost and availability. It would be the cats meow. (cats don't like being wet)

I've just searched through on the PO's documents on how he attacked this problem. Obviously "boat moisture" is a concern for most of us at one time or another during the boating year. In the PNW, it seems worst in the October-November months, but can "flare-up" during the winter when a cold-snap is followed by a pineapple express.

The PO was on a mission against boat moisture and placed “Hypervent" under the mattress and installed a "Circumvent" which is a stainless steel air exchanger. A web search reveals nothing about the device. I have several sheets of text, and a pamphlet referencing Circumvent International (a division of Nanaimo Humidity Control, the phone number of which is not in service!), a couple of other "not in service" phone numbers and a now defunct website: dry-out.com. "Circumvent" essentially consists of a DC fan, controlled by a humidistat. The unit is installed as low as possible in the bilge. When running, air is drawn from the bilge and piped outside the boat. The negative pressure created draws air back into the boat. The unit works when colder air from the outside, is warmed and the humidity drops (humidity is a function of temperature) and that air "dries out" the interior structures of the boat, and is then pumped outside the boat. Mattresses, clothing and blankets are moisture traps and these are dried out over time.

Clearly the system works best when there is a humidity differential between the inside and outside air: Cold outside air holds less water than warm inside air as the chart below shows. Overall, I think the "thing" works, and draws 1.4 amps when the fan is running, which over 24 hours when on the hook is 34 ah, so the draw when on the hook is important to consider. However, it is probably best to turn the unit off when the winter pineapple express rolls through as the outside air contains a higher humidity and replacing the low humidity inside air with outside air of higher humidity results in condensation in the bilge area.

Jim

Lutarious said:

Our aft cabin has a water tank under the bed. the cool water combined with out body heat makes for some condensation, so I put a layer of hard insulation across the top of the tank. It really helps a lot.

Click to expand...

That is exactly my setup.

seasalt007 said:

I went to the home improvement store and got several pieces of roof ridge vents. They are usually about 1" thick by 12"x 48". You can drill a few extra holes in each panel.

Something like this: Air Vent: Hip Ridge Vent

A lot cheaper than $10 per sq ft and work great.

Click to expand...

Interesting idea....

Bacchus said:

Don't mean to be picky... just trying to straighten out some technical terms that are sometimes confusing.

Condensation forms at what is known as the DEW POINT (YES - this is also saturation point for that temp - super saturation is something else again and probably outside the scope of this conversation).
Dew point is a function of the moisture content in the air - otherwise know as ABSOLUTE HUMIDITY LEVEL...
Not to be confused w/ RELATIVE HUMIDITY which as a combination of how much water is present (ABSOLUTE HUMIDITY) and the AIR TEMP (which affects how much moisture the air can hold at that (and only that) temp.
So - relative Hum changes as the air temp changes - absolute Hum (and Dew Pt) for practical purposes does not change w/ temp.

When the air cools to the dew point you get saturation & condensation.

The above - and a whole lot more - is covered in the US Power Squadron Weather Course - which is now available online as well as live through local Sail & Power Squadrons. See USPS.ORG if interested.

Click to expand...

:thumbs:

Actually, Bacchus is correct. Dew point is a measure of absolute humidity.

And the advice is correct.

A minor points, super saturation occurs almost in ALL clouds. Otherwise aircraft would pretty much never ice.