Dehumidifying Without Dehumidifier

[CaptainBob]

We're entering our second winter aboard now and the question of dehumidifying has re-arisen after finding the first drops of condensation in the back of the cupboards and under the mattress.

We've developed a pretty good system of ventilating and using the Eberspacher, and lifting the mattresses periodically. We have also now acquired a Meaco dehumidifier which we run in a cabin when we're not in the same cabin. This is all working OK.

The Eberspacher sucks in outside air and pumps it through the cabin, and out of the ajar hatches - drying us out a little as it goes.

But we're looking at getting a new boat and hopefully one with a drop fed diesel heater instead of the Eber. We like the idea of the glow of the flame and the ability to run it other than at full whack without the fear of it coking up (as per the Eber).

Does a drop fed fire with a chimney suck enough air through the cabin to effectively dehumidify it?

Are there existing systems which can suck in fresh air and effectively circulate it? I'm thinking of Heath Robinson style ideas involving Eber style ducting and an electric fan heater in place of an Eber installation. We only really use the Eber on shore power anyway and this would give all the benefits and none of the drawbacks.

A bit of a confused post I know. Basically looking for thoughts ideas and experiences.

Thank you!

 

[Downsman]

I'm not able to comment on the diesel heater but I have a solid fuel stove in my boat. I've never found the need to draw air into the boat by any means other than simply opening the main and fore hatches a little. With the stove going the warm air rising makes it's own circulation system and cold air falls in through the main hatch.
Certainly the temperature at cabin sole level is lower than head height so that is what appears to happen. (Not being a boffin I'm assuming that's the process) I sleep right forward where I also have a small dehumidifier switched to come on just periodically, I suspect that helps to draw air through the boat as well. Condensation is virtually nil through out the boat with the combination of dry heat and a little help from the dehumidifier, but I live alone which may be another factor.

 

[CaptainBob]

Cheers for the reply.

When we use fan heater only we start to get damp after a couple of days so I guess your solid fuel is pushing air up chimney and sucking in replacement air as you say - which sounds like it's working for you. Cheers!

 

[duncan99210]

The advantage of the eber is that it pushes air round the place, removing the damp air. It also pushes a much greater volume of air through the boat than the combustion air you'd get using drip fed heater. That said, it depends to an extent on how big the boat is and now many people there are on board; more people = more moisture (from sweat and breathing) so more of a problem to overcome.
We found that we 2 of us in a 40 foot boat, running the eber for an hour or so evening and morning kept the damp at bay. This year, we've got electricity included in the marina costs, so we're going to use a fan heater more than the eber: we'll have to see how it all works!

 

[saxonpirate]

Condensation...don't mention it...

Bob... it's an ongoing battle mate. I've spent plenty of years living aboard and quite a few of those in horrible climates like the UK. So pretty experienced in combating the dreaded condensation.

I've lined lockers with carpet and cork, had polystyrene under bunks, anti-condensation paint behind panels, left hatches cracked, all hatches open when cooking blah..blah... Have only ever used a de-humidifier when off the boat, all hatches closed down and a 100watt tube heater running. Result: boat dry as a bone. Don't really see the point of using a dehumidifier while onboard with hatches open...drying out the local area.

My last boat in Cornwall was a Beneteau First 35, big boat with a lot of volume and just me on it. I had a Dickinson Newport Diesel Heater which was a fantastic bit of kit and gave off lovely dry heat, plus a fan heater, 100watt tube heater and a 400watt infra-red heater. I'd be lying if I said the boat was as dry as a bone...it wasn't. Lost some books to mould, photo's sticking together....clothes damp in the hanging locker. Found the odd place where it seemed someone had thrown a bucket of water in the boat, crazy but true... it just seemed the nature of the beast.

Obviously the weather plays a big part duh! (how did I work that out) a week of non-stop drizzle in Cornwall though is enough to make a man slash his wrists. Nearly...nearly...nearly..... Alloy framed windows and hatches are my biggest whinge on a boat for condensation but it's got to condense somewhere. I can highly recommend the Dickinson heater for keeping you warm and it looks cosy because of the flame window. But as for stopping condensation....maybe the use of a snorkel vented to air while sleeping and always eating out to stop cooking down below...the choice is yours. Good luck....

 

[scoty]

condensation

After the UK, living on board in the Med. now 12years on,,,,,I have for the winter months a WEBASTO, hot air piped round the boat,summer time blows cooler air around ,, the Webasto is cheap to run (gas oil) yearly costs to maintain are, two hours of my time to clean burner, 6 euros, to replace the burner wick,solar panel charger keeps battery/s topped up,
much easier/cheaper than the Eber;
Fan heater used on accasions or as alternative,
31 footer very little condensation,,mainly due to cooking /galley is along side hatch entrance, (steam etc goes straight up and out)
Alternative is to put a sheet outside over all the boat, (makes a second skin) works well in constant minus temps,(north America)

 

[CaptainBob]

Thank you for the excellent replies!

 

[DaveH]

Hi....
I was recently looking for a ventilation system for my garage and also for my house which stands empty for long periods of time. The garage is in the basement, so would smell musty sometimes after returning from a couple of months away.

After lots of searching i found a system which uses what looks like a solar panel.
A solar powered fan draws in air from outside, and circulates it through this panel, drying the air before it enters the premises.
I'm pretty sure that they advertised a small unit that is for use on boats and caravans.

I'm not sure if forum rules allow me to mention the system name here, but i think if you google "solar ventilation system" you will find it.

Oh they were designed for Scandinavian climates so should work in less extreme climates.

Cheers.

Dave

 

[Liverboard]

Condensation

We have oil filled radiators and an electric fan heater for an extra boost which is great whilst in a marina. Also have webasco heating system which is very effective.

In areas that are little used or when the boat is on the hard for any length of time I put Moisture Mate which is a plastic container which is filled with calcium chloride crystals that absorb the moisture.

Must say, that we have hatches on vent and being old fashioned I open them wide whenever possible to let the air blow through.

We have aluminium frames round the marinised glass windows, but we only get condensation sometimes when I am cooking veggies due to the steam.

 

[hovepier]

more condensation ...

I have a 20ft fibreglass sailing boat. I'd like to fix the condensation problem but I'm reluctant to use mains electricity. Would a solar panel and extractor fan be effective without any heating?

 

[KellysEye]

In my experience any heater increases condensation, the amount of condensation is greater than the heater can dry. We always use a dehumidifier if running a heater, the amount of water it takes out of the such a confined space is extraordinary.

 

[CaptainBob]

Since I first posted up this thread, and thanks to the answers, I think I've totally sussed our condensation issues. We've not had _any_ for a while now.

All I'm doing is making very sure there are two openings as far apart from each other as possible at all times. If we're in the v berth then I open the main hatch and the v berth's hatch. If the v berth door is shut then I open the main hatch and the hatch at the forward end of the saloon. As a result there's a definite feeling of a slight flow of air.

And this is all using just an electric fan heater except at cooking times when we run the Eber on max for about an hour, with the two hatches open even wider still.

Working an absolute treat. I haven't used the dehumidifier for anything except when we'd done some washing and the tumble drier hadn't finished the job.

 

[MASH]

As you can get diesel powered fridges perhaps someone needs to invent a diesel dehumidifier, sounds like there's a market for it.
All ventilation does is to chuck your expensive heated air overboard with the mositure it is carrying and letting in fresh damp cold air to be heated in its place. That is not dehumidifying. There are only 2 ways to do that, afaik, chemically vis. silica gel or similar which is not practical on a boat-sized scale, or via a refrigeration aparatus which uses more electrical power than most boats can provide without shore power or a genny.

Edit..Brainwave!

How about circulating winter-cold water through a radiator matrix to condense the moisture and drawing ambient cabin air through it with a comuter fan, a thermal pump using your heater output or perhaps the eber fan to circulate the air you'd only need a tiny water pump for the condensing flow. Not very fuel efficient (dumping some heater energy overboard, but then that's what you were doing with the ventilation method in the first place) but it would probably work as long as the water temp was down in low single figures, but not if much warmer.

 

[CaptainBob]

As you can get diesel powered fridges perhaps someone needs to invent a diesel dehumidifier, sounds like there's a market for it.
All ventilation does is to chuck your expensive heated air overboard with the mositure it is carrying and letting in fresh damp cold air to be heated in its place. That is not dehumidifying. There are only 2 ways to do that, afaik, chemically vis. silica gel or similar which is not practical on a boat-sized scale, or via a refrigeration aparatus which uses more electrical power than most boats can provide without shore power or a genny.

Edit..Brainwave!

How about circulating winter-cold water through a radiator matrix to condense the moisture and drawing ambient cabin air through it with a comuter fan, a thermal pump using your heater output or perhaps the eber fan to circulate the air you'd only need a tiny water pump for the condensing flow. Not very fuel efficient (dumping some heater energy overboard, but then that's what you were doing with the ventilation method in the first place) but it would probably work as long as the water temp was down in low single figures, but not if much warmer.

Not a bad idea! Alternatively you could convert the Meaco dessicant (chemical) dehumidifier to have its heater diesel powered. The Meaco uses about 460W on max power, but I believe the majority of that is for heating - which could be replaced by something diesel fired I guess, and the moving parts could then easily run off the 12V system. Most people living aboard where it's cold enough that you'd need to worry about condensation do have shore power though I'd imagine.