pvb
Well-Known Member
Bavarias aren't exactly high-end pricing, if they can do it...
Practical advice on reducing overnight condensation please
- Thread starter alexincornwall
- Start date
Bavarias aren't exactly high-end pricing, if they can do it...
Scomber
Well-Known Member
a very big +1 john
sadler 29 with lots of foam filling no dehumidifier no extra insulation inside lockers proper under seating/bunks ventilation matting etc - keep the air moving -last season cut more internal holes in lockers and added vent covers to move air around more - we too don't have major problems -quick wipe round windows in a morning - it's simple science really, water vapour from any source will make for the coldest spots so keep it moving / open hatches when cooking / wet gear outside if poss etc etc
left our boat 4 months over winter - all seacocks out plenty of air moving through -dry as a bone when we went back - agree.... it's people cooking and wet gear
JohnGC
Well-Known Member
While it's true that warm air is able to hold more moisture than cold. It makes it better at moisture removal not worse. Because more moisture can be held in a given volume of air and will be removed by ventilation more readily. In addition, warm air will retain more of the moisture already in it from sources such as cooking and and expiration.
Warming the cabin air (using dry heat) will not create any more moisture. It doesn't affect the moisture generated by cooking, breathing or evaporation of the sea which is (I hope) outside the cabin not in it. What it may do is cause some condensation to evaporate which can then be removed by ventilation.
For ventilation to work, the air must be warm enough to hold the moisture you want to remove.
But, I accept that in spring, in the UK, in a small cabin, it is usually ventilation that is inadequate.
Scomber
Well-Known Member
agreed - a good blast of eber with ventilation before leaving or during use will seriously help to keep our boat drier than it otherwise would -
trick from a friend we have adopted is have a bowl of fresh water in cockpit and swill off salty feet before going below - keeping salty water and things soaked in it out of the boat will also keep the moisture levels lower since salt absorbs water (it's hygroscopic!)
trick from a friend we have adopted is have a bowl of fresh water in cockpit and swill off salty feet before going below - keeping salty water and things soaked in it out of the boat will also keep the moisture levels lower since salt absorbs water (it's hygroscopic!)
AntarcticPilot
Well-Known Member
My experience recently might help.
Up until last year, I kept Capricious on the Clyde. This meant that our visits were infrequent - at best once a month, and often less. So I decided to move her south at the beginning of last year. During our passage, Capricious was used for 3 weeks without a break, and we used either an electric fan heater when shore power was available or the Eberspacher if it wasn't. Obviously ventilation was also much improved simply because we were using her and the companionway was open much of the time. We'd never had much of a problem with condensation, but at the beginning, she felt rather cold and clammy, and a lot of thing left aboard were damp. After three weeks, she was bone dry, and has stayed that was as we have been able to occupy her much more - and last year was not a good year for me, as an old back problem flared up again, and I had surgery a few weeks ago - I am pleased to say that it seems to be 100% effective.
Anyway, the lessons learnt are:
1) Using your boat will dry her out better than anything!
2) A source of heat that does not release water vapour into the cabin is essential.
3) Ventilation is essential, but need not impact on keeping the cabin cosy at night.
Incidentally, as an aside I'd note that a fan heater on shore power is actually about the cheapest and most efficient mode of heating available!
Up until last year, I kept Capricious on the Clyde. This meant that our visits were infrequent - at best once a month, and often less. So I decided to move her south at the beginning of last year. During our passage, Capricious was used for 3 weeks without a break, and we used either an electric fan heater when shore power was available or the Eberspacher if it wasn't. Obviously ventilation was also much improved simply because we were using her and the companionway was open much of the time. We'd never had much of a problem with condensation, but at the beginning, she felt rather cold and clammy, and a lot of thing left aboard were damp. After three weeks, she was bone dry, and has stayed that was as we have been able to occupy her much more - and last year was not a good year for me, as an old back problem flared up again, and I had surgery a few weeks ago - I am pleased to say that it seems to be 100% effective.
Anyway, the lessons learnt are:
1) Using your boat will dry her out better than anything!
2) A source of heat that does not release water vapour into the cabin is essential.
3) Ventilation is essential, but need not impact on keeping the cabin cosy at night.
Incidentally, as an aside I'd note that a fan heater on shore power is actually about the cheapest and most efficient mode of heating available!
JohnGC
Well-Known Member
You have reminded me that Mallorca mountain villas early in the season can be a bit damp for the first 1 or 2 days. Presumably because they have been shut up for a while with inadequate ventilation.
After the first couple of days they tend to be bone dry.
Good news on the surgery.
alexincornwall
Well-Known Member
Thank you everybody, lot's of sage advice and ideas to try out here.
We prefer anchorages where possible, purely for the solitude (and because the kids get up early so we avoid disturbing other residents), so the focus needs to be on solutions that don’t require shore power, hence ruling out the dehumidifier.
The Dufour is certainly single skinned with no insulation so in the short term we’ll wrap up warm and concentrate on the ventilation.
We prefer anchorages where possible, purely for the solitude (and because the kids get up early so we avoid disturbing other residents), so the focus needs to be on solutions that don’t require shore power, hence ruling out the dehumidifier.
The Dufour is certainly single skinned with no insulation so in the short term we’ll wrap up warm and concentrate on the ventilation.
RupertW
Well-Known Member
Dehumidifiers are a great answer and we have one running all winter draining into the sink. What we find is that it makes a huge difference starting dry even if, like you, we spend time on board at anchor.
Every bit of clothing, headlining, cushions and woodwork are dry when you come on board and open the hatches. After that then ventilation, ventilaton, ventilation after leaving the marina. Forehatch always slightly open so that warm moist air has somewhere to go.
My guess is that all the myriad moisture absorbers on the boat slowly go from dry to slightly damp with the ventilation slowing down the process. If you start with them all damp you are losing from the word go.
Every bit of clothing, headlining, cushions and woodwork are dry when you come on board and open the hatches. After that then ventilation, ventilaton, ventilation after leaving the marina. Forehatch always slightly open so that warm moist air has somewhere to go.
My guess is that all the myriad moisture absorbers on the boat slowly go from dry to slightly damp with the ventilation slowing down the process. If you start with them all damp you are losing from the word go.
ctva
Well-Known Member
Ventilation, ventilation, ventilation.
As others have mentioned, everything else is just masking the symptoms of moist air and cold surfaces.
We have a Jeanneau 34 so very similar. Over winter when on shore power, the dehumidifier does the trick, nothing else required except a bit of warmth as they will not work below about 5c unless it is an absorption one (can't remember the posh name but we have one in the house).
For the rest of the year and not on shore power there are three things that we have found that work.
First, ventilation, a solar vent. Even in Scotland with the limited sunlight this was a revelation on our first boat which we kept on a mooring. Get the one that fits a Tannoy vent with a built in battery so that it charges during the day then switch it on at night. Best thing since sliced bread and worth every penny. When we leave the boat we just switch it to on all the time mode so it vents all day during light hours. The result is that the boat stays fresh and dry for when you return with no boaty fusty smell.
Second, ventilation, we leave the companion way and forepeak hatch and door open. In winter, yes it's fresh but a good duvet works. It also encourages shared bodily warmth, nudge nudge wink wink!!
Third, ventilation under the bed. Here we use the air mesh that can be cut to shape. This allows the moisture that is transmitted through the mattress (an awful lot) to escape. However this will only partly do the job. Unser the mesh I have used the foam jigsaw squares, about 2' sq, that are readily available cut to the shape of both beds to act as insulation. This we have found leaves the mattress dry which in turn will be warmer. It is the same for the duvet as dry bedding is far warmer. People often complain about the cold, close all the windows in the mistaken thought that this will keep them warmer where the opposite is true, ventilation drys out the bedding which is then more efficient and warmer.
Solar vent.
As others have mentioned, everything else is just masking the symptoms of moist air and cold surfaces.
We have a Jeanneau 34 so very similar. Over winter when on shore power, the dehumidifier does the trick, nothing else required except a bit of warmth as they will not work below about 5c unless it is an absorption one (can't remember the posh name but we have one in the house).
For the rest of the year and not on shore power there are three things that we have found that work.
First, ventilation, a solar vent. Even in Scotland with the limited sunlight this was a revelation on our first boat which we kept on a mooring. Get the one that fits a Tannoy vent with a built in battery so that it charges during the day then switch it on at night. Best thing since sliced bread and worth every penny. When we leave the boat we just switch it to on all the time mode so it vents all day during light hours. The result is that the boat stays fresh and dry for when you return with no boaty fusty smell.
Second, ventilation, we leave the companion way and forepeak hatch and door open. In winter, yes it's fresh but a good duvet works. It also encourages shared bodily warmth, nudge nudge wink wink!!
Third, ventilation under the bed. Here we use the air mesh that can be cut to shape. This allows the moisture that is transmitted through the mattress (an awful lot) to escape. However this will only partly do the job. Unser the mesh I have used the foam jigsaw squares, about 2' sq, that are readily available cut to the shape of both beds to act as insulation. This we have found leaves the mattress dry which in turn will be warmer. It is the same for the duvet as dry bedding is far warmer. People often complain about the cold, close all the windows in the mistaken thought that this will keep them warmer where the opposite is true, ventilation drys out the bedding which is then more efficient and warmer.
Solar vent.
Greenheart
Well-Known Member
Again, no help to the OP, but the old 'Solarvent' (trade name?) seemed to me to have solved the problem of damp on unattended boats, when it appeared maybe 30 years ago...
...but I think you need two, so one can suck outside air in through the forehatch, while another sucks cabin air out, at the companionway (no closed doors between them)...
...so the tiny fans aren't fighting any pressure gradient. Granted it wouldn't suck in dry air on damp days, nor all night, but that constant change of air all of every day, is a godsend.
...but I think you need two, so one can suck outside air in through the forehatch, while another sucks cabin air out, at the companionway (no closed doors between them)...
...so the tiny fans aren't fighting any pressure gradient. Granted it wouldn't suck in dry air on damp days, nor all night, but that constant change of air all of every day, is a godsend.
Bru
Well-Known Member
Sorry, but it is not bad advice at all.
It does depend on the type of heating though. Simply heating already moisture laden air inside the boat will, as you say, increase condensation
However, a heating system that draws air from outside the boat, heats it (and consequently reduces it's moisture content) and then pumps it into the interior ... or in other words a blown air heating system ... massively reduces condensation. In fact, as I already said, based on personal experience of living on board a badly insulated (but well ventilated) yacht through the UK winter, it virtually eliminates it
Erk! Oh no it isn't! (Is it panto season yet?
)Or to be more precise it depends on how much you are paying for shore power. And (if you've got diesel heating) how much you're paying for diesel
I've posted the figures before but running a 2kw fan heater costs me (at our marina prices) more than double the cost of running a 3.9kw Webasto. I grant our shore power costs are a bit steep at 21.something p per kw/h and also that over winter I'm declaring 100% domestic use on the diesel but even with cheaper shore power and more expensive diesel the cost of running the fan heater is still higher
And the blown air is MUCH more effective. A 2kw fan heater will heat the saloon OK, just about (it'll struggle to do even that when the outside temp is below freezing) whereas the Webasto will heat both the saloon and the forward cabin to comfortable levels whatever the outside temperature (and the aft cabin too on the rare occasions it's used over winter)
Plus, as mentioned above, the fan heater heats and recirculates the air already inside the boat which, if anything, makes condensation worse whereas the blown air replaces the air in the boat with fresh dry air
I would only use electric heaters over the blown air if I was on fixed price or inclusive shore power. On a metered supply the blown air is first choice every time
pvb
Well-Known Member
As an aside, all the references to blown air heating here assume that cold outside air is drawn in to the heater, which is the correct way. However, previous threads have often suggested that many DIY installers draw cabin air into the heater, so as to minimise heat loss, and the condensation issue is just one reason why recirculating cabin air is such a bad idea.
Greenheart
Well-Known Member
Fascinating contributions. I think 'ctva' pipped me to the post on Solarvents - I'd thought it was an original, obvious solution, though not to nocturnally perspired/respired moisture.
As somebody currently yachtless, who detests being cold and damp (and refuses to acknowledge that sailing accommodation necessarily must be chilly and moist), I wonder why, in an age when such a lot of technology is carried aboard, and plenty of power-hungry systems are coveted, adopted and recommended, many yacht-owners still cling to no-tech ascetic solutions like encouraging thicker pyjamas and a through-draught on very cold nights?
Is it just the pursuit of simplicity and disinclination to invest any time and money in a solution?
I haven't more than a grain of understanding of physics, but I believe systems called 'heat-recovery dehumidifiers' manage to suck out the mild sweaty air from a cabin, passing the warm exiting flow over a very thin metal manifold, on the other side of which is the incoming cold dry air. So while one is getting rid of the damp, one can recover some of the warmth present in the damp cabin air, and use it to raise the temperature of its fresh dry replacement. Clever stuff, although beautifully simple and totally obvious, really.
Has anybody such a system on board? If not, why not? I can't believe it's down to cost, considering what owners are ready to shell out on winches, comms and espresso makers.
As somebody currently yachtless, who detests being cold and damp (and refuses to acknowledge that sailing accommodation necessarily must be chilly and moist), I wonder why, in an age when such a lot of technology is carried aboard, and plenty of power-hungry systems are coveted, adopted and recommended, many yacht-owners still cling to no-tech ascetic solutions like encouraging thicker pyjamas and a through-draught on very cold nights?
Is it just the pursuit of simplicity and disinclination to invest any time and money in a solution?
I haven't more than a grain of understanding of physics, but I believe systems called 'heat-recovery dehumidifiers' manage to suck out the mild sweaty air from a cabin, passing the warm exiting flow over a very thin metal manifold, on the other side of which is the incoming cold dry air. So while one is getting rid of the damp, one can recover some of the warmth present in the damp cabin air, and use it to raise the temperature of its fresh dry replacement. Clever stuff, although beautifully simple and totally obvious, really.
Has anybody such a system on board? If not, why not? I can't believe it's down to cost, considering what owners are ready to shell out on winches, comms and espresso makers.
ctva
Well-Known Member
That's the one that we have at home! They do draw more power, 250w I think so definitely a shore power connection needed.
TiggerToo
Well-Known Member
I don't know if this is what you are talking about (https://www.meaco.com/dehumidifier/...-dd8l-junior-dehumidifier-multi-award-winning) but we have something like this whose function seems to be exactly what you describe. It produces a lovely stream of warm air, and litres of (essentially) distilled water to be used for all sorts of interesting things.
But it is the dry, warm air which is the fantastic thing in a boat. Pity only it does require a 240v plug. Still, over Easter we used it to have a VERY DRY boat to start with (just run it when we were at the pontoon with a power socket), and then adopted the "ventilation/heating (Ebby..)" routine over at the Isles of Scilly (no shore power) and stayed more or less dry, and certainly not musty, for a week.
The dinghy over the open forehatch was a great innovation, though!
thinwater
Well-Known Member
Lots of partial understanding and misinformation.
Ventilation Alone. When the outside temperature is pleasant, ventilation is generally enough. You can't get condensation if the humidity is the same inside and out. Well, that is mostly true, something summer sailors don't understand. If the water is cold, or if there is snow on the deck, the hull can be considerably colder than the air, and thus the more you ventilate, the MORE condensation you get. I'm not saying that is what the OP is talking about, but early season sailors know that cold water really draws condensation, if the hull is uninsulated. Summer sailors will not notice this.
Dew Point. You will have condensation anytime the hull or window temperature is below the dew point. That means that adding heat, if parts are uninsulated, will not always stop insulation. As one poster pointed out correctly (and was falsely criticized), heat without insulation can make condensation worse, because the hatch temperature has not changed much, but the air is holding more water. Thus, unless you are going to keep the air very dry, there is no substitute for insulation, both hull (if not cored) and windows. Won't single-glazed windows in your house sweat and frost? Of course they will.
Dehumidifiers. Consider the tiny thermo electric units (Eva Dry etc). They can be run on solar. I've had one for 7 years. I run it on a timer. Keeps the boat very dry, about 55% RH.
Heat. Ventilation is great unless you mind freezing. Drawing combustion air from the cabin sounds good, but it's damn wasteful; perhaps that works if it is cool, but not if it is cold (-10C is common here in the winter). My heater draws from outside, and the RH stays at 50-60%. The trick is to minimize generation (there is a fan in the shower and I cook many things using retained heat).
You need to understand RH (relative humidity) and dew points. All surfaces must be above the dew point, which ventilation alone will not always accomplish, not if people are adding any moisture at all, since the RH outside will be right at 100% during the wee hours.
Ventilation Alone. When the outside temperature is pleasant, ventilation is generally enough. You can't get condensation if the humidity is the same inside and out. Well, that is mostly true, something summer sailors don't understand. If the water is cold, or if there is snow on the deck, the hull can be considerably colder than the air, and thus the more you ventilate, the MORE condensation you get. I'm not saying that is what the OP is talking about, but early season sailors know that cold water really draws condensation, if the hull is uninsulated. Summer sailors will not notice this.
Dew Point. You will have condensation anytime the hull or window temperature is below the dew point. That means that adding heat, if parts are uninsulated, will not always stop insulation. As one poster pointed out correctly (and was falsely criticized), heat without insulation can make condensation worse, because the hatch temperature has not changed much, but the air is holding more water. Thus, unless you are going to keep the air very dry, there is no substitute for insulation, both hull (if not cored) and windows. Won't single-glazed windows in your house sweat and frost? Of course they will.
Dehumidifiers. Consider the tiny thermo electric units (Eva Dry etc). They can be run on solar. I've had one for 7 years. I run it on a timer. Keeps the boat very dry, about 55% RH.
Heat. Ventilation is great unless you mind freezing. Drawing combustion air from the cabin sounds good, but it's damn wasteful; perhaps that works if it is cool, but not if it is cold (-10C is common here in the winter). My heater draws from outside, and the RH stays at 50-60%. The trick is to minimize generation (there is a fan in the shower and I cook many things using retained heat).
You need to understand RH (relative humidity) and dew points. All surfaces must be above the dew point, which ventilation alone will not always accomplish, not if people are adding any moisture at all, since the RH outside will be right at 100% during the wee hours.
Kelpie
Well-Known Member
What you need is a Mechanical Ventilation Heat Recovery unit. As fitted to new houses which are built properly (i.e. airtight).
You can get small single room versions which are basically a bathroom extractor fan, but with a heat exchanger. I know of one model which draws a couple of watts and runs off 12v.
If you go down this route, you really need to make the MVHR the only pathway for air in and out of the boat, though. Boats are obviously inherently well sealed up but don't underestimate how hard it might be to seal the companionway or cockpit lockers, or a keel stepped mast.
Still Grinning
Active Member
Hi Kelpie - I would be interested in the model you are referring to that runs off 12V? A google search only showed up 240V models....
Thanks in advance!
Thanks in advance!
Kelpie
Well-Known Member
From memory I was thinking of the Ventaxia HR25- but I just googled to check and it's 24v, and unfortunately also discontinued! My bad, sorry. There are still a few around on eBay etc and of course it's not impossible to obtain the necessary 2w at 24v on a boat.
If I ever get round to doing this on my own boat, I would really like to find a unit that can be installed vertically, as I have a big trunking in the saloon which would be perfect for it. Otherwise I would be looking at a horizontal unit installed in a cockpit locker with the vent in the cockpit.
If I ever get round to doing this on my own boat, I would really like to find a unit that can be installed vertically, as I have a big trunking in the saloon which would be perfect for it. Otherwise I would be looking at a horizontal unit installed in a cockpit locker with the vent in the cockpit.
pvb
Well-Known Member
The HR25 uses a power supply which only outputs 8v for low speed operation, so could probably be fed with 12v without drama.
Note that many 12v heat recovery devices work on 12vAC, not DC, so care is needed when buying for boat use.