Dry Mat?

Stemar

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Jazzcat has a 190 x 140 double mattress of 100mm foam in the forward cabin. This sits on the solid GRP bridgedeck, and we're getting condensation under it. Even in favourable weather, wrestling a double mattress out of there through the galley to air is something of a spectator sport, except there's no room for spectators, so I don't want to have to do it too often!

Is there anything better than Dry Mat to stop it? Height is limited, as our feet go under the foredeck and only just have enough space.
 

Boathook

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Jazzcat has a 190 x 140 double mattress of 100mm foam in the forward cabin. This sits on the solid GRP bridgedeck, and we're getting condensation under it. Even in favourable weather, wrestling a double mattress out of there through the galley to air is something of a spectator sport, except there's no room for spectators, so I don't want to have to do it too often!

Is there anything better than Dry Mat to stop it? Height is limited, as our feet go under the foredeck and only just have enough space.
I used dry mat and it did improve things. The double mattress is in 2 parts, split length ways on my 9m. I did consider slats but it would mean cutting away the grp bunk base. I don't think that is structural but just a lot of work for not much gain

I've also put on a cheap memory foam topper, one piece, cut to size to improve comfort. Reduces the height a bit but not as much as expected.
 

thinwater

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Most of the breathing products are based on cedar shingle underlayments, such as ...
Cedar Breather® Ventilated Underlayment | Benjamin Obdyke

I don't know what the UK brands are, but they may have this at the building supply store.

The other things that help are vapor barriers around the mattress and waterproof insulation on the pallet (it only condenses because the pallet is colder than the air).

Also remember that these breathing enhancements only work if the bedclothes don't hang over the edge, blocking them.

Good luck! I used wrapped mattresses with open cell mattress toppers on top. No problems, even through the winter.
 

Lucy52

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I was getting condensation under the mattress, I used drymat which has cured it, but I wish I had turned it up along the edge of the mattress, as this would prevent bed clothes coming into contact with any damp on the sides of the hull lining.
You will get condensation just from your breathing, never mind cooking, and this needs either ventilation, or use of a dehumidifier to keep the boat dry.
When cutting drymat you will get numerous little bits of plastic, which will get everywhere, keep them off your bedding and clothes, better yet, do it outside.
 

Stemar

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I was getting condensation under the mattress, I used drymat which has cured it, but I wish I had turned it up along the edge of the mattress, as this would prevent bed clothes coming into contact with any damp on the sides of the hull lining.
You will get condensation just from your breathing, never mind cooking, and this needs either ventilation, or use of a dehumidifier to keep the boat dry.
When cutting drymat you will get numerous little bits of plastic, which will get everywhere, keep them off your bedding and clothes, better yet, do it outside.
Thanks for the tip. One side is open to the air, the other and head and foot are GRP, so I'll run it up the sides. How easily does it bend? Thanks also for the point about bits of plastic. I was expecting to do it on the pontoon, but better do it where I can sweep up.
 

Dellquay13

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Thanks for the tip. One side is open to the air, the other and head and foot are GRP, so I'll run it up the sides. How easily does it bend? Thanks also for the point about bits of plastic. I was expecting to do it on the pontoon, but better do it where I can sweep up.
It bends easily. I have a double layer of drymat, the marketing blurb says it can be easily joined with the smallest size cables ties, and that’s how I keep the two layers together. I oversized mine so one layer goes up the sides of the mattress in the forepeak.
In very cold weather (Dec-Feb) when any cooking or boiling the kettle gets the rest of the boat dripping like a rainforest, I still get a bit of condensation on the bed base, but the underside of the mattress stays dry.
 

Neeves

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We used 'sprung' Ikea bed slats, 2 pieces overlapping for a double mattress. One set was under a thin mattress, 2" of foam, we never felt the slats. When we bought they did not supply a double slat, you used two singles (narrow singles). Even though they were narrow they were still, combined and installed correctly, too wide. Cuting one set down would not really work, as you would end up with no spring on one side. The idea of cutting both equally seemed a lot of hard work.

I simply overlapped the two sets, on set fell between the slats of the other set.

When we originally bought they made the curved bed slats, a bit later they stopped selling (in Australia) the curved slats and only sold flat slats. Later they re-introduced the curved slats. Don't know what they do now. Originally we only used slats on one bed. But we have 2 identical double berths and then did the second, because the first was so successful.

If you remain concerned of feeling the slats - buy two camping sleeping bag mats. They are thin and a dense foam, maybe 10mm thick (every back packer seems to carry one one their rucksack). Lay this over the slats and your foam mattress on top.

Jonathan
 

OCuea

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Would a 12 volt fan or a few of them and some hose do any good to ventilate? If you have the battery capacity?
 

Neeves

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Our double berths were ply, with a space underneath and then 'half' the underside of the bridge deck. The gap was about 50mm

I drilled the ply with a 2" hole saw to offer some ventilation between and ply (with mattress on top, and later slats with mattress on top), and the fibreglass of the bridge deck and also drilled to allow ventilation from the enclosed space, under the ply, and the rest of the cabin. I sourced little grills to make the holes look professional. I did think of wiring in computer fans - but it proved unnecessary.

I do note that none of this is valid for the OP as his mattress sits directly on the bridge deck.

However I would suggest he looks at having the slats, if that's the route he takes, arranged under the mattress with the slats running so that the gaps between the slats faces 'out' and the slats thus can 'self air'. If its an island bed - the slats could be open at both ends.

Another suggestion - when not using the berth have a device to lift the mattress at one side, like a short tent pole, and this will allow the mattress, again, to self air.

Jonathan
 

Boathook

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Jazzcat has a 190 x 140 double mattress of 100mm foam in the forward cabin. This sits on the solid GRP bridgedeck, and we're getting condensation under it. Even in favourable weather, wrestling a double mattress out of there through the galley to air is something of a spectator sport, except there's no room for spectators, so I don't want to have to do it too often!

Is there anything better than Dry Mat to stop it? Height is limited, as our feet go under the foredeck and only just have enough space.
Isn't the bunk in the forward cabin on an interior moulding ? The bridge deck is on a slope but the bunk is level ?
 
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