Practical advice on reducing overnight condensation please

[alexincornwall]

Hi all,

The family and I have been making the most of the generally decent Spring weather by spending a few nights on the boat (Dufour 32). All is well despite the chilly evenings and our lack of effective heating, though we are suffering quite badly with condensation, particularly in the f’ward cabin (which also holds the water tank). By the morning, we literally have water dripping onto us (and the bedding) from the ceiling, particularly around the hatch areas. Obviously not a particularly comfortable experience. Strangely the kids, who reside in the aft cabin, seem to be almost completely unaffected.

I see that the topic has been covered in a few posts previously, with suggestions mainly geared around insulation and dehumidifiers, however we’re off again at the weekend (anchorage so no shore power) and I wondered if anybody had any immediate tips on improving the problem?

Does leaving a hatch window open reduce the effect?
Does covering the glass hatches make any difference?
Is the f’ward cabin more prone to suffer because of the water tank below?

Any ideas, experiences or solutions very gratefully received. It’s critically important that the wife’s happiness levels are kept high at this stage of the season!

 

[thinwater]

Yes, storm windows really help. This one dripped on my bed. If these are hatches that accept removable insect screens, replace them with 1/8" acrylic sheet. External covers also help, either canvas or closed cell foam.


You can also insulated with bubble wrap (wet with a spray and it will stick).

Install heat. I added a Dickenson P9000 and love it.

Obviously ventilation helps; the there is always heavy dew in the spring, so without heat damp is always a problem. The forward cabin simply has a higher ratio of people and hull surface area to ventilation and volume, and probably more airflow (cooling) on the outside.

 

[TiggerToo]

Hi all,

The family and I have been making the most of the generally decent Spring weather by spending a few nights on the boat (Dufour 32). All is well despite the chilly evenings and our lack of effective heating, though we are suffering quite badly with condensation, particularly in the f’ward cabin (which also holds the water tank). By the morning, we literally have water dripping onto us (and the bedding) from the ceiling, particularly around the hatch areas. Obviously not a particularly comfortable experience. Strangely the kids, who reside in the aft cabin, seem to be almost completely unaffected.

I see that the topic has been covered in a few posts previously, with suggestions mainly geared around insulation and dehumidifiers, however we’re off again at the weekend (anchorage so no shore power) and I wondered if anybody had any immediate tips on improving the problem?

Does leaving a hatch window open reduce the effect?
Does covering the glass hatches make any difference?
Is the f’ward cabin more prone to suffer because of the water tank below?

Any ideas, experiences or solutions very gratefully received. It’s critically important that the wife’s happiness levels are kept high at this stage of the season!

you've said it.... a dehumidifier is the answer. A "proper one", i.e. one that needs a nice 220/240V supply... sorry...

Having said that, covering the hatch with something well insulating (e.g. we had a nice big tender upside down on the forepeak and left the hatch open) made a huge difference to the condensation in the forepeak over Easter...

Tigger is a Dufour 35, so not too unlike yours.

I don't think the water tank below the bunks makes any difference whatsoever to condensation, unless it is leaking, that is...

 

[Kelpie]

Ventilate as much as you can, even if you end up wearing three layers of thermals under your PJs! It's important to have a good airflow right through the boat. Simply opening up hatches without thinking about the airflow will not have the same effect.

The best tip I've found for windows is to cut up a cheap foam camping mattress to make covers that are an interference fit on the inside of the window. This has the double benefit of being a blackout blind.

Cooking is a major source of water vapour- always drain pans of pasta etc over the side, not at the galley.

 

[alexincornwall]

Having said that, covering the hatch with something well insulating (e.g. we had a nice big tender upside down on the forepeak and left the hatch open) made a huge difference to the condensation in the forepeak over Easter...

Tigger is a Dufour 35, so not too unlike yours.

Thanks, that's a good shout that we can try out immediately. Incidentally I think we were on the opposite side of the pontoon from you a couple of weeks ago...

 

[duncan99210]

The main reason the forecabin has more condensation than the kids aft cabin is because there's two adult breathing and sweating moisture into the cabin as opposed to much smaller volumes produced by the kids. If it's not raining (and it hasn't been in Cornwall recently!), then crack the hatch open and prop it open to allow the air in.
If you've got a two piece companionway hatch, removed the top piece to provide an exit route for the air flow. Do this even if it's raining, as the sprayhood will keep the rain out, especially if you're at anchor.
Insulation is always something of a losing game, as it will never prevent enough heat loss to totally stop condensation. Ventilation is the cheapest and simplest method of reducing the problem, and even if you have to put on an extra cover or your thermals.

 

[Alfie168]

Through ventilation...lots of it, and hot water bottles inside decent sleeping bags or under duvets.....and in my case as I've started to feel the cold a bit more in my 60s.....socks and a woolly hat!. I can get quite snug in my freezebox that way.

Tim

 

[Greenheart]

Insulation is always something of a losing game, as it will never prevent enough heat loss to totally stop condensation.

I'm reluctant to believe it, but hearing it is very disappointing. Along with the absence of blown-air ducted ventilation on yachts, the lack of insulation seems to me to be one of those cost-cutting exercises by builders, led by customers who won't fork out for better specification, all happy to let the domestic side of sailing improve at a snail's pace.

It almost makes me glad that whatever yacht I buy will need to be shabby enough to be cheap - because I'll want to gut the interior anyway, to line the hull and fit ducting.

 

[Bru]

The only really effective solution is a combination of insulation, ventilation and, above all else, effective heating

(Dehumidifiers deal with the result of condensation, not the causes)

From experience living aboard in the UK winter, the improvement that has all by itself virtually eliminated condensation in the v-berth is blown air heating (relying on the existing fixed vent and we haven't even begun to figure out what to do about insulation yet!)

The cheap option, as described, it's to wrap up as if your half way up Everest and open the hatches so that the inside is as cold as the outside! I'm getting far too old for that myself

 

[Angele]

If the exterior humidity is reasonably low (as it has been recently) then, as others have already said, simply leaving the hatches slightly ajar will solve your problem.

A couple of weeks ago, I went to bed with the hatches fully shut (because I had forgotten to do anything before I got in bed) and, come the morning, the ceiling was covered with water drops - exactly as you describe - both in my cabin and in the saloon.

The following night I left the deck hatches ajar and woke up to a boat that was totally dry.

If it is foggy/raining outside then it is difficult to eliminate condensation without a dehumidifier.

 

[JohnGC]

As Etap owners, we have a double hull and the space between is filled with foam. Apart from making us unsinkable, it also provides a lot of insulation.
There is an image of the foam half way down this page, http://www.yachtingmonthly.com/gear/trying-to-sink-an-unsinkable-boat-31338

It's noticeable, that we have less condensation than similar boats with a single skin construction. But unless we take other steps we still get more than we would like . As you would expect the condensation forms first on the aluminium extrusions around the ports and the ports themselves long before it forms on the insulated hull.

Even with all that insulation, the inner GRP skin can be cold enough to form condensation.

We have never needed a dehumidifier. But as others have said, getting the ventilation right and adding some dry heat if you can really helps.

Do you sleep with your cabin door closed? If so, try it open or partially open.

We added a Froli bed spring system, it was intended to improve the mattress comfort. But its biggest benefit was that it eliminated condensation under the mattresses. https://4reifen1klo.de/froli-bettsystem

Don't forget that burning gas generates water (1.8kg of water per 1kg of butane burnt if my Googling has turned up the right answer). So adequate ventilation after brewing your bed time Horlicks may help a little.

I suggest improving the ventilation first as it costs little or nothing. After that, heat, insulation and maybe a dehumidifier, but they all cost.

John

 

[ibbo]

A piece of tarpaulin material suspended over the forehatch makes a massive difference to the drips. I'm sure part of the problem is the dew drop in the early hours of the morning.

Mike

 

[ianj99]

The best tip I've found for windows is to cut up a cheap foam camping mattress to make covers that are an interference fit on the inside of the window. This has the double benefit of being a blackout blind.

I use stiff 6-8mm foam panels sold as garage floor mat or exercise mat works horizontally if cut slightly oversize - the springyness keeps it in place. I use it in the hatch cutouts as well as portlights so it avoids the need to keep them open and it acts as a blackout as well.

 

[lpdsn]

you've said it.... a dehumidifier is the answer. A "proper one", i.e. one that needs a nice 220/240V supply... sorry...

+1. Unfortunately.

Natural ventilation sounds good, but in early spring the air has a high relative humidity so it won't dry out much of the dampness that's already there. At least it's marginally better than winter. Zygrib will actually give you a forecast including RH so you can see what to expect.

Even if you can't regularly use a de-humidifier, do it when you can to dry each cabin so you're at least starting from a better position. Ventilation whilst sleeping will also help some moisture escape.

If there's any sun, layout the bunk cushions in the cockpit to help dry them, but watch out for the next shower.

Look on the bright side, it's worse in Ireland.

 

[KellysEye]

We used a dehumidifier next to the sink and a pipe into the sink, that way we could run it all the time and not have to keep emptying the water catchment bowl.

 

[theoldsalt]

Despite several posters recommending heating this is bad advise and will not prevent condensation; in fact it makes condensation worse as warm air holds more moisture than cool/cold air - so more moisture is in the air to condense on cold surfaces.
So wrap up warm and open the hatches to allow cold air to flow through the boat.

 

[pagoda]

The only solution with lots of bods on board is to FORBID BREATHING.

People put out silly amounts of transpired moisture, added to by cooking/ boiling kettles and washing!

Unless it's peeing outside- leave a hatch and companionway open- get a through draft?

 

[pvb]

I'm reluctant to believe it, but hearing it is very disappointing. Along with the absence of blown-air ducted ventilation on yachts, the lack of insulation seems to me to be one of those cost-cutting exercises by builders, led by customers who won't fork out for better specification, all happy to let the domestic side of sailing improve at a snail's pace.

Don't be disappointed, I don't think it's true. My Bavaria has foam-cored topsides, hull liners, and a double-skinned deck structure. It all seems to insulate very well, and the only condensation I get in the forecabin is on the metal frame of the forehatch. I always have the hatch slightly open at night - ventilation is very important.

Most Eberspacher and Webasto blown-air heaters have a cold air ventilation setting, although I wouldn't want to leave it on all night.

 

[Caer Urfa]

I stay aboard for min a week every month all year round, ventilate ventilate its as simple as that. I leave two side windows open the gap thickness of my thumb and leave my companion
way door cover open an 1", yes its cold in the night but at least I am dry!

You won't get much sleep with anything electrical running so get yourself a nice hot water bottle and ventilate

 

[Greenheart]

My Bavaria has foam-cored topsides, hull liners, and a double-skinned deck structure. It all seems to insulate very well, and the only condensation I get in the forecabin is on the metal frame of the forehatch.

That is encouraging - but I wasn't thinking that 'foam-cored' glassfibre construction counts as insulation! :biggrin-new: It isn't, is it?

I know zip about insulation, really. But considering how damp and chilly all unlined bare GRP cabins feel in the low season, I've always believed a proper job of purpose-designed, professionally-applied insulation on the inside of accommodation areas, must be as important to comfort, as fitting a heater...

...and how much more effective (and cost-effective) will a heater be, when wintry winds and chilly deeps are kept out by more than a few millimetres of cold hard glassfibre? I know no modern boats are as austere as that, but if the inner surface of the hull isn't lined, damp will still accumulate, and the inner, 'tactile' bulkheads aren't going to be materially warmer than the space behind them.

And I doubt it's beyond the wit of designers and yards to find neat-looking insulative materials that could be moulded to cover shiny metal through-hull components. And even double-glazing...not exactly space age, is it.

It isn't an answer to the OP's request for quick-fixes, and at the end of the winter, the observation may not be very well timed...

...but I think it's unfortunate if designers' and builders' understandable pursuit of economy, perpetuates the seasonality of UK sailing.