Condensation under main cabin bed

[zz000mm]

Hi All,

I have a Bavaria 49 and have a problem with condensation under the mattress within the main cabin. The result is that the bed is very cold and I have condensation build up under the mattress which makes the mattress damp compounding the problem.

I have installed a 'Dry-Mat' under the mattress and have purchased a topper to go over the mattress.

I have also switched off the dehumidifier and opened all the cabin hatches slightly to allow air in.

The problem still persists and I have condensation under the main mattress and now under the topper.

In the space under the bed there are three compartments. One filled by the front fresh water tank and the other two spaces simply empty.

There is constant condensation on the inside face of the hull below the waterline within this space.

The ventilation of the space is very poor. There are timber access boards over the space which have large holes, but this is simply covered by the mattress.

No problems elsewhere.

Any ideas would be gratefully appreciated.

 

[dunedin]

Go visit a caravan dealer and take a look under the bunks.

Many years ago they solved this problem by replacing bunk boards with slats of wood, joined using webbing tape to maintain spacing. I retrofitted these to an old caravan and the difference was immediate and huge.
Easy to make up, provided you have a staple gun. Only issue might be will add perhaps 1/2 inch of height compared to plywood

They also fixed the wet bedding due to condensation on the side - by adding hardboard trim set 1/2 inside the wall. But best not to attempt these as drilling the walls of a boat could be detrimental !

No idea why boats haven't adopted this (though this was perhaps the only example of sensible caravan engineering - otherwise the quality was rubbish)

 

[Neeves]

We had a similar problem. We fitted slightly cambered Ikea bed slats. Then they sold the slats as a roll, each slat fitted into a rubber pocket, the pockets were on two long rubber ribbons. We have a conventionally sized queen and used 2 singles, we did need to cut about 15mm of the bottom few slats of one unit to fit. Our bed base has a slight fiddle that stops the whole lot falling on the cabin sole (but its a cat so not much of a heel). If you need to add a fiddle, you need to have slots in it to encourage the airflow. I think now Ikea sell the cambered slats in a frame, so you might need to discard the frame, but I think they sell simple slats as a kit (but the camber seems better and you could make a flat one yourself (just buy some 40mm x 10mm boards and staple to tape, that's what simple Ikea bed boards are). As suggested caravan shops are another option - but try your local bed shop or other knock down furniture suppliers.

Anyway, the slats solved our problem.

Again cannot think why boat builders have not thought this one through, its not expensive and you are not alone!

 

[Seajet]

Some boat cushions have a vinyl underside, which makes condensation much worse.

My boat has thick foam cushions with a denim underside, directly on top of flat wooden bunk tops, and there is simply no condensation; I do always leave ventilators open at bow and mainhatch.

A lot of people prop the cushions up at one side or end to remove contact with the bunk top underneath - things like baked bean tins are a common method - when leaving the boat.

 

[RAP77]

google
froli sleep syatems

 

[Neeves]

google
froli sleep syatems

Really good, but a bit pricey, especially if you have a queen, sized bed

Jonathan

 

[Rossynant]

Many years ago they solved this problem by replacing bunk boards with slats of wood, joined using webbing tape to maintain spacing.
No idea why boats haven't adopted this

This is (was at least) known and used on boats. One thing to consider: solid wood (plywood) under a mattress gives warmth, as is an insulator. Sailbunks or pilotberths made with canvas under mattress is another way, but then a mattress was made twice the thickness to overcome the cold getting at the occupant from below. Good for tropics though.
Any slatting put under will ventilate the mattress, but unless condensation is a problem while one sleeps there I would do without. No problem to put the mattress up on something when not in use.
The clue to most problems like such on boat is ventilation - of the whole cabin. And then thermoinsulation so not much condensation occurs. Most boats have both inadequate, or lacking. Such is a fact of life.

For instance on 30 footer: 6 dorades with good cowls, 2 hatches, slatted companionway. Inside every side panel ventilated behind. Was advised to put some dehumidifier or heater in, but was leaving for long and decided to rely on this vents.
Bunks not ventilated in any way, vinyl lies on plywood. And left wet sails loosely folded on them to dry
No sign of wet under mattreses (or anywhere) standing closed but not covered for almost a year in Wales. But then this is design from the area, so made for this, I guess.
All the outside was in mould, algae and moss, jeeez...

 

[LadyInBed]

You need to put some form of insulation under the hatches under the bed and put an air gap under the mattress.
As suggested, the Ikea slats can be used under the mattress, or what I did was make a grid using the insulation tubes (as used for water pipes in the loft). I held them together with cords threaded through the centres.

 

[Neeves]

The last thing we need is insulation (or not from cold), its going to be 43 degrees today!

 

[Rossynant]

Then put the slats under, yessss. Another idea is a kind of dense grating, like for bathroom floor. Look for such that's 'open' on below, so air will circulate where it should.
It's getting down to -10 here, so I was thinking other way But then again - the coldest boat in the tropics was one made to go north-west passage, lots of insulation all over. Stayed cool inside...