Dehumidifiers for winter storage

[tony_brighton]

How about in the heads?

Does the dehumidifier just let the water dribble out or is there any kind of pump action?

To get it lower down can you trail the outlet into the head rather than the sink?

 

[Guest]

Re: moisture

Right, the air is holding tiny bits of water vapour. To start, the air is slooshing around the cabin. But then you close all the doors and go home. Now the air is still. If you dehumidify, then there'll be dry air (which will be lighter and tend to rise) and wet air (heavier) so this will lurk at lower level. So, best to dehumidify at ground level, not at sink level.

Some boats with gas on board (if the haven't switched off the gas) and v sensitive alarm, occassionallty have to "bail out" the gas from the bilges to get the alarm to go off, as the gas is heavier than the air. Same principle.

This weeks Physics experiment is to get two of those pathetic £1 moisture eaters things, place one on a very top shelf away from potholes (which would cool it, atrract more moisture and spoil experiment) the other on cabin sole, and note how the one at lower level is sopping wet on return next weekend, other is less so. I'm afraid that I am sad enough to have already done this, proving that moisture is more of a problem at lower levels.

 

[robp]

Re: How about in the heads?

Dribbles out Tony. As Matt says, let the bilge pump do the rest.

 

[mica]

I think everyone agrees that dehumidifiers are well worth it, but all this talk about how to dispose of the water - what a waste.

Ours can produce up to 5 litres per week, that is the size of the holding tank and we decant it into old water containers, for use in topping up our car radiators and the boat's fresh water cooling system. We find this a cheap form of distilled water, thus preventing limescale in our engine's system. Not suitable for batteries though, in case it contains impurities.

P.S. This too is a B & Q £99 job, two years on and coming up for its third winter, it is still going well and we have not had any problems with it at all .

MICA

 

[Mel]

It seems to me that people who use dehumidifiers are very happy to see the water collect on the assumption that it is drying the insde of their boat. I however believe that what they are actually doing is drying the earths atmosphere. Most boats have some ventilation with the atmoshere outside and it is a matter of physics that gases (including water vapour) will move from high concentrations to low ones by a number of processes including absorption.

I leave my boat well ventilated over winter and I am very content with the results.

 

[Plum]

Mel, you are absolutely right. If you use a dehumidifier in the boat you must block up all the vents. If you have enough ventilation then you don't need a dehumidifier. A dehumidifier and open vents together is a waste of energy.

 

[Bergman]

Re: moisture

If wet air falls and dry air rises why do clouds form in the sky?

 

[johndf]

dehumidifiers, clouds, fog.

We ran our £99 B&Q dehumidifier for 3 hours pe day using a £5 B&Q timeswitch. We collected around 3 or pints per week on average, until I arranged continuous drainage intothe sink. This winter i'd better put it lower down in the boat.

As to why clouds form in the sky, it's because rising air cools as it expands and once it becomes fully saturated, water begins to condense out of it. The more it rises, the more the water condenses. Why does it rise at all? - it only rises if the air is unstable (ie much colder aloft than at ground level). layer cloud stays whwere it is because of relatively warm air above it preventing any more rising.

However, you can see moist air falling when shallow fog forms on a still Autumn night. We had some beautiful patches on Tuesday morning. You could see the fog flowing out of a field and down the road!

 

[LadyInBed]

Is a Heater better

On a Marina would a small fan heater (or two) not do a better job?

 

[boatone]

Re: moisture

I think those 'pathetic little moisture eater things' are bl**dy good!!!!!
I used two of them on a centre cockpit fibreglass Norman 32, one in each cabin, and was amazed at how much moisture they collected and how sweet they kept the cabin air during the long winter months- even got to leave the cushions etc on board. Wouldnt be without them now and no electricity needed. Buy large (5kilo) refill drums from B&Q for about £8 I think - enough crystals to last for a full season and I still keep them in action right through the summer. I did get two rather nicer containers from B&Q - round and dumpy rather than the little oblong things you see in Woollies.
'Pathetic' - not at all....humble maybe but I luv 'em.

boatone@boatsonthethames.co.uk

 

[Twister_Ken]

Worse? Fetid swamp!

Then you'd have warm humid air which would rot things quicker.

 

[jollyjacktar]

I fell off my cabin trunk laughing.

Best entertainment I have had for ages. Almost made me stop drinking. A little bit of basic science knowledge would go a long way to stop the sales of dehumidifiers and would prevent people trying to dry up all the moisture in the world. This was probably the fate of the planet Mars and the Martians succeeded at the task.

Common sense tells us that the dehumidifier is just setting up a cyclic action. You dry some air, the air becomes moistened from other moist air and you dry some more. Well perhaps in a vacuum you may succeed, but then in a vacuum where would you put the condensed moisture, which would instantly vapourize and start things over again. Great for electric power suppliers, dehumidifier servicemen, manufactureres etc and so the money go round keeps on keeping on.

Everyone knows that colder air has a lower vapour saturation level. Best leave the fridge door open and cool the boat and mosure condenses. But then the air would heat up and then we would have to start over again, but hang on, isn't that what a dehumidfier does any way. Well why bother, in winter it is cooler, ergo less moistue in the air. Well can you win anyway.

Oh yo yo ho I still can't stop laughing. However there are still a bunch of believers around who think the world is flat, the moon is green cheese, free rotating props are less drag when you are sailing and that centrifical force exists. Long live the beelivers and down with the rationalists. This is the scuttlebut forum isn't it . Yo ho ho and a bottle of rum. ))))))

 

[incognito]

I have read this thread with amusement and disbelief.

The theorists about the atmospheric behaviour inside boats have a lot to learn, and the experiments are misleading. The only way to prove things is to do them and see what happens.

First, the DH... they work by pretending to be fridges, and we know that the moisture in a fridge ices up on the element - that is how they work. However, that just produces ice, which is OK for the drinks, but will just make the boat heavier. The cheaper DH will switch off the fridge, and rely on ambient temperature to defrost the element into the draining arrangements. This is OK unless you want the thing to work below freezing. (See heater comments as to why this may be OK).
The more expensive DH will reverse the fridge cycle, and defrost the element not relying on ambient temperature.

We have an expensive DH from CruiserMart, cost about £299, I think, but that was cos I had not done my homework, I believe the B&Q version would be just as good at £99, but I have never seen it so don't know.

Now, this is our third year with a DH, and this is how it is for us (NOT a theory).

Current boat 36ft (previous was somewhat smaller). Following applies from about October to April.

When leaving boat after sailing or check-visit. All ventilators shut, as I don't want to DH the whole world! No special sealing of the normal atmospheric leakage. Engine access open with small greenhouse (non-fan) heater set to come on at low temp in close proximity to engine bay. DH set to 70% Rh (mine is settable and has a continuous setting, but never used it, puts elec.bill up). Most clothing and bedding removed from normal storage and placed on berths (probably unnecessary). All sea-cocks closed except kitchen sink. DH stood on draining-board beside sink, with a little tilt to the left (otherwise the built-in tank takes priority and turns DH off when full) and drain tube led to sink. Greenhouse Min/Max thermometer placed judiciously away from heater and DH.

Results: everything stays dry and nice-smelling. Normally, when you pick up something which is cold, then any dampness makes it FEEL cold and damp. We do not have that, all our cold stuff feels cold and dry and instantly warms up under our touch (try it yourself on your boat!). We used to get light mildew up in the hatches, where the relatively warmer air (heated by the seawater) condensed out on the hatch-glazing. We also used to get condensation all year round under berth cushions, after a good night's sleep, always had dampness under cush. We have neither of these symptoms anymore (even in season, never dampness under berths).

Max/Min never goes below zero, even though only 500W greenhouse heater (which means the DH could be a cheaper version, see above). I think this suggests that I am not exchanging my internal air much with the outside.

Finally... we reach September with some water in the bilges, below strum box pick up. By the end of October, mid November, our bilges are dry, although the bottom of the bilge is nearly 6ft below the DH.

I am not good on theories, but maybe the seawater heats the air, relatively, and causes a natural convection - maybe it is the blower in the DH? I don't know, but I have told you the way it is, not the way I think it might be.

I note what someone posted about ventilation - on our 23ft Sonata we used to rely on ventilation - standing all our berth cushions on one edge when leaving, to allow clear air flow... NEVER ENOUGH!!! The cold damp air of the Medway would come in and set up a high Rh, and each spring we had smelly everything. I think this was amplified by the fact that the moisture brought into the boat during the sailing season was soaked up by all the boat's fabric and never really dried before the winter (maybe, I don't know, just another untried theory!!).

 

[Guest]

Re: seacocks

I'm pretty sure this has been done to death elsewhere, but the AD31P has raw water to the heat exchanger, picked up via the leg, and no seacocks. The raw water pump is just above the waterline, so changing an impeller in a swell could be a gas...

 

[Footpad]

Re: Crystals

I've not looked at these things; but if the crystals are silica gel (I think), like the little sachets you sometimes get when you open the box of a nice bright shiny new electrical gadjet, then you can recycle them by drying them out at home in the oven.

 

[boatone]

Re: Crystals

Nope, completely different. These crystals almost completely disappear as they do their stuff and the container needs to be refilled every so often. The fluid trapped in the tank below the crystals has a 'caustic' smell and feel to it.

boatone@boatsonthethames.co.uk

 

[pugwash]

Re: moisture eaters

How often do you have to change them? Coudl you leave them a couple of months? Your idea sounds great but the problem for me is getting to the boat during the winter.

 

[boatone]

Re: moisture eaters

I leave them several weeks, maybe even a couple of months without any problems. The lower container eventually collects perhaps a pint or more of water which I empty from time to time. Worst that couild happen is that all crystals are used up and lower container gets full. Suppose it could possibly overflow but never left it long enough to find out. Interesting thing is it seems to carry on working even when most of the crystals have gone.
If you want to experience the product Woollies sell the same sort of device for about £4-5 fo a container and one charge of crystals. Theirs is about 10" long by 3" wide and about 3" high. Forget what they call it but if you cant find it let me know and I'll check next time I'm in a store. I seem to remember seeing them in some hardware shops and also in Caravan Accessory places.

boatone@boatsonthethames.co.uk

 

[boatone]

Re: moisture eaters

The type I use are in the Cruisermart catalogue page 194 and called condensation moisture trap

boatone@boatsonthethames.co.uk

 

[paul]

Re: I fell off my cabin trunk laughing.

What's your point? Seems like you're saying they're a waste of money. I think a few thousand people-including me- would be inclined to disagree based on experience. Sounds like your boat isn't a dry one anyway - based on your drinking habit. Cheers!