Condensation Under Bunk Cushions

discovery2

discovery2

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I have recently noticed that after a night's sleep, there is condensation under the bunk cushions. Although it dries fairly quickly, it will also probably cause the cushions to deteriorate more rapidly.

I have seen a couple of 'solutions' including (sprung) slats but they seem rather expensive.

Can anyone confirm if the slats are effective (and worth the money), or what have folk 'invented' to alleviate the problem?

Thanks in advance for any ideas.
David
 
A common one seems to be to buy a cheap Ikea bed and use the slats from that.

I like the look of these. Click for link





**Usual disclaimers apply**
 
Over a period of 8hours, your body sweats a lot of moisture which ends up in your matress. It's like pouring a cup of water on your bed so this will build up if the matress is not aired.

The slats are the best but we have the rubber covered suff too though it is not as effective and I have found I still have to lift the matress during the day.



M
 
You don't need to buy a bed, just buy Ikea slatting.

The solution as ever is ventilation, ventilation, and more ventilation. The more air that flows, the better. If there is any way of providing air flow under the bunk - cuttting ventilation through, or even opening up under bunk storage
 
Unless you are happy to lie in an ever-increasing mouldy semi-hard swamp of your own and others sweat the only real solution on board is to put the mattresses out every morning and let the wind dry them.
 
We use ventair, the crumpled plastic between frabric. This is cheaper than the coir and certainly than 'chandlery slats' (don't know about ikea!)

In winter, living aboard, still have to air mattress regularly. No problems this time of year. We have also insulated (closed cell foam) the underside of the hatches of the lockers under the bed. And as said before - ventilate as much as possible with dorade vents, hatches ajar etc.
 
Lots of solutions for this- slats, rubberised coir, plastic mesh or for DIY, half sections of pipe insulation glued onto the base. A search on 'bunk condensation' will find extensive threads on this topic.
 
If the upholstery is the same material on topside as in bottom, make a bottom with more transpirable cloth...never synthetic, best is cotton.
Any advise about bunks, spreaders, etc. is good, but simpler to drill some holes in whatever is below the matress to allow some ventilation.
Best is to take off tho warm climates and have the portholes open while you sit aroud a gin and tonic watching the sunset.
 
Its nothing to do with sweat and everything to do with condensation.
Warm air on cold surfaces condenses.
 
I forked out on the Bedflex slats.. (no IKEA nearby..) . They work a treat and have increased the 'spring' So no condensaton and no bruised shoulder or hips.

(no connection with supplier)
 
Cobra25 is entirely correct. It is all to do with sweat and little to do with condensation.

The body in the bunk increases the humidity of the air around it. Moisture is driven through any permeable material down a temperature gradient ie from warm/hot towards cool/cold, until it meets a vapour barrier.

So, in the bunk, the moisture is driven down through the mattress to the cooler under mattress area by the warmth in the bunk until it meets the vapour barrier of the bunk top where it will collect and pool regardless of the temperature of the bunk top (except, unless the bunk top is warmer than the temperature between the bedding and the mattress occupied by the sleeper).

If one ventilates between the mattress and the bunk top, as many do, condensation can still take place on the bunk top but, of course, only if the bunk top temperature is below the dew point but, of course, the ventilation allows it to evaporate away and the damp problem is usually mostly solved regardless.

The other solution is to provide a vapour barrier on the top of the mattress so that the moisture in the bunk cannot be driven down through the mattress, and this method is absolutely 100% successful, always (pretty obvious I would have thought but the comment always attracts the non believers). It is important to have permeable over bedding then so that the moisture gets driven up through the bedding out of the top of the bunk to the colder air in the cabin.

Many forumites do not believe the above, in which case I can only suggest they clarify the matter for themselves with an architect or HVAC engineer well versed in building insulation (especially buildings with high temperature gradients through building fabrics, such as occurs in cool stores, etc)

If the bunk top is replaced by slats (replaced, not lain on top of it) or holes are cut through it into the locker space below the bunk as is often suggested, then one has to be careful to ensure that that space is well ventilated (it usually is not in modern production boats). Is kinda obvious (well it is to most) that the moisture will then be driven down into that space possibly leading to mildew, etc problems there if the boat is occupied for any length of time.

Taking all of the above into account it becomes easy to cure any bunk moisture problems in normal climates.

John
 
Thanks for that Ship's Cat John.

It's amazing how you never notice the condensation/sweat unless you spend a week living on your boat. A weekend is fine as the moisture evaporates slowly during the workdays and then it usally isn't a problem. Thing is that the moisture builds night after night until the bed is very damp.

It is worse on a foam mattress so you could change the mattress for a custom made sprung one. I simply do not like foam mattresses. The slats work well but you could use the rubber doormats too, you know the ones made of large holes held together with rubber :-)

Good cruising


M
 
Thanks folks for all your comments. Whilst I appreciate there are many factors involved in causing, and reducing, condensation (including sweat!) it is very useful to hear opinions and comments from others.

Happy boating/sailing - lets hope this Summer is a good one!
David
 
As already mentioned in another post, the body expires something in the region of one half to one pint of water overnight. Most of that moisture seems to be absorbed by the mattress and, if the mattress is in contact with a cold surface, the moisture will condense onto that cold surface.
IMO, allowing ventilation under the mattress is only part of the answer. I use a belt and braces approach by preventing that moisture getting into the mattrss in the first place and also having ventilation under. I cover the mattress with a waterproof sheet, covered in turn with a flanelette sheet. I also wear pyjamas on the boat (I sleep naked at home). It is much easier to air pyjamas and flanelette sheets than it is to air mattresses.
I use a belt and braces approach
 
The cheapest solution that provides ventilation and an increase in comfort is to go to B&Q or the like and buy lots of loft pipe insulation tubes then lay them under the mattress.
You can string them together with about three inch lengths of tube as spacers.
 
I bet you two have showers on your boats, because sleeping so near an impermeable barrier would be a bit masochistic otherwise!
 
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