under bunk condensation - what really works

Burnham Bob

Burnham Bob

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Never had a problem with condensation till now but with horrendous rainfall and the damp air even our boat's ventilation couldn't cope. No problems on the bunks with lockers beneath them and ply boards as tops but SWMBO's bunk is on a fibreglass moulding and was really wet. Absolutely not a leak.

So - there are several mats that increase circulation under the bunks but which really works? Or is there another idea? This happened whilst the boat was in the marina and not as it was being used.
 
We have a set of wooden slats under our mattress which largely eliminates any damp problems. It's also more comfortable than just the mattress. Ours were a boat specific set, bought when we still employed and had money. IIRC they were about £150 or so. You might be able to cut that cost down somewhat by buying some IKEA bed slats and mounting them on a couple of bits of 2x1 timber.
We've used one of the underlay open mesh type mats as well be weren't impressed by its performance in comparison to the slats.
 
We use the open mesh underlay between foam mattress and plywood base, but it still accumulates condensation over a few nights. We need to lift the mattresses every few days to dry everything out.
 
Another vote for the slats, I used some bought at the Southampton boat show, sprung with a curve so they kept the matress off the base. They could be cut down to fit thye shape of the forepeak and worked well. Whenever the boat was not in use I always lifted the matresses an stood them on edge, consequently never had subsequent condensation or damp problems.
 
DavidMcMullan said:
We use the open mesh underlay between foam mattress and plywood base, but it still accumulates condensation over a few nights. We need to lift the mattresses every few days to dry everything out.
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We have the same, remarkable difference BUT it aint cheap
I have some Ikes slats that i never got around to fitting- open to offers :)
 
Regularly discussed here.

We have solved our issue with Dry Mat, like many others. Good value, easy installation and will will keep air between mattress/cushion and the surface under-

sh_boatshow-8.jpg


No shares, just a happy customer
 
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In my opinion, most of the views on underbed condensation work on the principle that improving ventilation could reduce the problem. However, I have been out in Houston, Texas with the temperature in the 30 degs C and seen condensation on the OUTSIDE of windows, because the air conditioning was cooling the windows, below the dew-point of the outside air. No shortage of ventilation here, but condensation has occurred.

So I think the major way to avoid condensation is to prevent warm moist air coming in contact with a cold surface. Sailing in Scotland, the water temperature varies between 8 and 14 deg C and so the bilges are probably around this sort of temperature. (Great for storing wine and beer) Earlier this year I finally finished insulating under the fibreglass bed bases in the back cabins using 25mm PIR insulation board.

http://www.jewson.co.uk/building-ma...l-eurothane-gp-insulation-2400-x-1200-x-25mm/

I stripped the aluminium foil of one side and glued the board underneath the bed bases using Evostik Serious Stuff or Stick Like Sh*t adhesive or Unibond No More Nails.

On the various hatch covers, I cut them to size and left a suitable hole so you could still lift them.

The Result
Over a two and half week sailing holiday this summer (?), we did not have a suitable opportunity to air out the bedding in the cockpit tent, as we would normally do on a weekly basis. In the port cabin there was a small area of condensation around 20cm across, but there was not enough moisture to wet a tissue. In the starboard cabin, the only area of moisture was on the cover of the battery box, which I had not been able to insulate. On both beds we use Ventair insulation from Largs Chandlers
http://largschandlers.co.uk/products/chandlery/

(Like Hypervent) and in the areas of condensation, there was a small amount of moisture on the bottom layer of the matting, but nothing on the mattresses (We find that this is better than Dry-Mat). The mattresses and bedding, including those parts tucked in down the side of the mattresses, were all dry. Make sure the Ventair is exposed on as many edges as possible to maximise air movement

The other point is that if you are running diesel heaters, then you will be pulling a lot of moist air into the cabin when there is high humidity outside. So in marinas when it is cold, we often will run a dehumidifier when the Webasto is switched on, or alternatively use an electric fan heater.
 
Spi D said:
Regularly discussed here.

We have solved our issue with Dry Mat, like many others. Good value, easy installation and will will keep air between mattress/cushion and the surface under-

sh_boatshow-8.jpg


No shares, just a happy customer
Click to expand...

Found that to be a total waste of time even with it curled up at the sides to allow better air ventillation
 
I know it must be obvious but here goes anyway. When the bunks on our boat are not in use the pads are lifted and left on their edge. One you get in to the habit you do not even notice doing it. If the problem is occurring when the boat is in the marina unused it will cost nothing to try it. Slats and mesh need air travelling past to work and that can be difficult to maintain.

As a minor diversion; we cover the cushions in the main cabin with loose covers made from Ikea fleece blankets which are comfortable to sit on, stay in place and very rapidly washed and dried, they match the cushion colours too, (dark blue Alcantara) . This was a tip placed on here by he who is now known as Jumble Duck, for which I always meant to thank him.
 
Warming the locker under the bunk would help, filling it with something like unrotted horse manure might do the trick, though I would prefer to dehumidify the boat myself.
 
Slats work. And they are available also from Compass, not a lot for a comfortable and dry bed. Used 365 days a year without condensation although the windows steam up a bit.
 
When this subject has come up previously, someone suggested using lengths foam pipe insulation. This year I tried this and it works, a few lengths of pipe insulation, some tape, a pair of scissors and half an hours easy work and the job's done!
 
Our previous boat had cushions on fibreglass and we put down capillary matting. Cheap solution and easy to cut to size from a roll. Problem solved.

We repeated the exercise with our current boat and result was almost as good but not quite. Our berth sits above a water tank, not just an empty locker. I checked the tank surface and it was damp. Everything was fine after I put metallised bubble wrap directly on top of the water tank. So combination of capillary mat and insulation required in the end. Both of these were very cheap to buy so worth trying.
 
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Mistroma said:
Our previous boat had cushions on fibreglass and we put down capillary matting. Cheap solution and easy to cut to size from a roll. Problem solved.

We repeated the exercise with our current boat and result was almost as good but not quite. Our berth sits above a water tank, not just an empty locker. I checked the tank surface and it was damp. Everything was fine after I put metallised bubble wrap directly on top of the water tank. So combination of capillary mat and insulation required in the end. Both of these were very cheap to buy so worth trying.
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Doesn't the capillary matting end up waterlogged ?
 
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