Major mattress moisture help! (PNW)

[Lepke]

You need better ventilation or maybe a different heating system.

I'm in the PNW and in the winter my relative humidity runs about 35-40% because I run a stove. My mattresses are all dry as are my clothes and bedding without any more care than in a house.

All your shower and cooking steam, plus your breathing stays in the boat unless vented. Running a vented heater/stove exchanges the air. Because of the cold, many people totally close the boat and then have moisture problems.

[Cpt Mark]

I live on the Columbia River in Portland. We get more rain and cold then Puget Sound and in the winter, I've seen the river freeze over at the edges. I use the Froli system and have no issues anymore. Below my bunk is the water tank so it's solid ply on top. I do keep air moving in the winter.

[Don C L]

Originally Posted by Steve Bean

Has the mattress ever been wet with salt water? This would make it hard to keep dry, as salt is hygroscopic.

My first thought too.

[LargeMarge]

We full-time live-aboard since 2003.

We built our bunk using expanded metal.
This material is a criss-crossing wire of diamond holes.
Without a solid plate of plywood, plenty of air reaches the underside of the mattress.

Each morning, we open all the windows.
During cool weather with propane heat, we open windows on each wall for the heated air to evacuate humidity.

[SV__Grace]

I feel your pain. We are full time, all season cruisers who love the PNW and this will be our second winter. Some thoughts for you based upon what we've learned so far-

1. Insulate- our boat was built for the higher latitudes and already has a lot more insulation than the Catalina, but we needed to add more. Insulation will decrease the air spaces prone to condensation (above, below, and the sides, ideally), and make the rest of your solutions more effective (heat, air circulation, etc). If you have exposed fiberglass, cover it. If you have wall and ceiling panels, add insulation in the space between the cabin and the hull.

I knew that I would probably need to do this, but it's a big, intimidating job. Having condensation rain down on us last winter motivated me to over come my resistance and this was a high priority project this past summer.

2. Moisture barrier- I would guess that adding a moisture barrier underneath the berth will help a lot. The water tank is not the problem, the drive shaft area is because it's under the waterline, close to and open to under your bed. Something like this might work well, and you could go thinner.

3. Hyper Vent- we use it and it works for us, even though we make the bed instead of stripping it to dry every day. You would think the bedding would prevent air flow but somehow it works. Our bed is @2 feet above the waterline in our aft cabin over the rudder quadrant. We do air out the area once a month or so.

4. Air circulation- gotta remove all that moist air that you create while breathing for 8 hours in the area somehow. You need positive pressure forward for your intake, and negative pressure aft for your exhaust. If passive vents don't work you need fans, such as the day/night solar vents. We have 6 of them and they don't recharge well enough during the winter, so one of my projects is to add computer fans on switches for each one so they can work during the short, overcast days of winter here in PNW. I found fans small enough to fit in the opening tube and the electrical draw is very modest. We live on the hook so I'm very sensitive to use of power, but I'd rather be dry.

5. Heat- most, if not all of the problem will go away if you keep the heat high enough to decrease the humidity. We actually LIKE the cold and last winter ran our hydronic heater no more than a dozen times. Bundling up and cuddling are some of our favorite things to do! BUT, we had consistently had 75-85% humidity in our cabin, which made for way too much condensation. We plan to install a Dickinson style diesel heater so we can have it on low, drawing no power and sipping diesel, as an economical way to solve this problem.

6. Windows and hatches- we had a LOT of condensation on our windows and hatches, especially the ones with aluminum frames. A friend suggest using window film, and we did, and it was a miracle- NO condensation on the windows and hatches! I call it "shrink wrapping" and it was an easy job to tape the edges, cut the film, place it on the tape, and use a hair dryer to shrink it to fit. Did not interfere with visibility at all. Easy to remove at the end of season, and cheap to use annually as part of your winterizing routine.

That's it for now! Let us know how it goes!

[FionaJC]

We had this in our caravan, I was determined to eliminate it when we bought a boat. I have installed slats below the matteress. Just high enough to ensure a vent when the bed is empty and just low enogh not to cause discomfort. The slatting is "L" shaped so there are slats up the side covered with a thin sheet of ply. If that isnt clear then PM me and Ill post a drawing.

[Katkiln]

Thanks all- fantastic ideas so far. I got a humidity gauge and am seeing how it changes every day based on the new things I’m trying.

Yesterday I got a waterproof mattress cover and found the moisture about 1/2 what it was the day before so definitely making progress.... running the diesel heater for about 30 minutes and lifting the mattresses got rid of any remaining damp.

Have a larger dehumidifier arriving tomorrow and will see how that changes the damp- currently at 68% humidity in the cabin.

[tomlisasail]

We had an issue with one of the aft berth cushions intermittently feeling damp when we would arrive at the boat to take it out. We searched everywhere for a leak. We just recently discovered that a 22 gallon water tank was beneath the cushion. When we would fill the tank after our last trip the water would leak out of the cap on top of the tank until the level dropped. We can't get the tank top to not leak I'm afraid the cap with break. The boats a 2001 Catalina 36. We're going to try not filling that tank till the boats loaded so that with a more aft cg the water won't be gravity fed to the cap. Good luck wet mattresses are worse that a wet sleeping bag.

[Katkiln]

@tomlisasail: that’s exactly what our VBerth does when we overfill the water tank but the aft does not leak.

Good news tho.... the dampness is mostly gone and avg humidity is a consistent 55% on shore power and 65% on the hook. The things I have done are:

- Froli below mattress System (more for comfort than moisture- but it’s helping)
- waterproof mattress cover
- synthetic (polar fleece) sheets that don’t absorb and wick moisture
- 13pint dehumidifier running when on shore power 24/7 or gen 2-3 hours a day
- “butterflying” or raising the mattresses daily for air flow (sounds like a chore but raising the corner 12” with a water or wine bottle really keeps it dry.)
- always keeping the hatch slightly open on dry days

Thanks for all the great ideas!!