Tackling condensation under the bed. Froli / Air Mat

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Phil_boat

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We've slept a few times in the boat now and yesterday morning realised underneath the cushions (it's not quite a mattress being only about 80mm thick) was very damp. I think it's a combination of condensation forming on the hull sides and running down the edge of the cushion and condensing against the top of the lockers. It's obviously not a new thing as there's evidence of them being wet from before we bought it.

I'm going to get either some air venting underlay

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Or if it's worth it some of the Froli springs.

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Obviously the Froli system is a lot more expensive, is it worth it and does it work well with thin cushions? Also I have a locker lid of around 50cm square which I assume I could screw a small number of the squares on to so it can still be removed?

Cheers!
 
I have a double layer of dri-mat under our foam which has helped a lot with condensation. The two layers are held together well enough with a few tiny cable ties.
It wasn’t totally successful though, so I fitted a 80mm 12v computer fan into the lid of the locker to force airflow through the matting, and that has proved a good combination. Our case may be a bit extreme though, as we stay on the boat in the winter too.
I run the fan for 15mins in a morning, and I bought a ball bearing version instead of the cheaper roller bearings as it is installed horizontally.
Other people report good things from gluing foam sheets like kingspan to the underside of the base board and locker lids, to reduce the warm/cold interface at the mattress
 
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I have the froli system and it did massively reduce the condensation issues. I managed to buy it on fb marketplace so wasnt expensive. Another option is timber bed slats. I also sit bed cushions on their end after we get up to air
 
Yes the IKEA slats is a very easy way to address under cushion damp.

Makes it more comfortable too with some give or springyness beneath.

Standing the cushions up before you leave the boat also helps.
 
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Since the only way to remove damp is ventilation, I can't see using the foam stuff or foam backed carpet being any good. Our slats put about a cm between the base and mattress. Combined with the large access holes in the baseboard ply that vents into the bilges, plenty of air circulating around underneath the mattresses on our boat.
 
There are always a flurry of these threads in the spring. Cold water/bilge/hull + warm humid air, and more importantly, humidity (about 1/2 pint per night per person) released into the mattress while you sleep. It is the season. While venting under the mattress helps ...

  • Do not make the bed in the morning. It needs to dry.
  • Do not let the bed clothes hang sheets hang over the edges during the day. This will block your new venting system.
  • Sealing the mattress (waterproof cover) and using a mattress topper works better. The moisture never gets into the mattress. I lived aboard and cruised in a cold climate for a little while.
The moisture needs to get out of the mattress, preferably through the top, before it can condense on the colder (cold water--remember?) mattress base. The difference between this and home is that in the spring your bed support is cold. Ventilation suports alone will NOT prevent condensation.
 
I’ve gone for the ventilated mat first to see if it improves things and will take all the suggestions above on board.

I can see how foam / insulation under would help things too and it would stop condensation forming on a cold surface.

Oh it’s also a pretty small bed & space so lifting the cushions isn’t that easy as we need the space for storage when we’re not asleep.

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wonkywinch said:
Since the only way to remove damp is ventilation, I can't see using the foam stuff or foam backed carpet being any good. Our slats put about a cm between the base and mattress. Combined with the large access holes in the baseboard ply that vents into the bilges, plenty of air circulating around underneath the mattresses on our boat.
Click to expand...
No, not the only way.

Another way is to block the moisture. I used sealed mattresses (vinyl cover) with thick foam toppers for years, including living aboard with snow. Luxuriously comfortable, like home. The moisture primarily comes from your body when you sleep, about a pint each night, and it has to go somewhere. I left the overs open in the morning and never had any condensation. Not when on the boat. Not when away. Same with my current boat (sealed mattress plus topper), no problems. It is not a very dry boat and there is water in the bilge. But no condensation under the mattress, and I am in a humid area with a wide temperature range (-20 to 40C). We had ice you could walk on this winter, and it's 35C today (freak spring heat).
 
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