I have a small boat with a cabin sitting in a yard with no mains power available. The inside is quite damp - if I had power I'd slap a dehumidifier in there like a shot. The next best thing I can think of is to spread lots of silica gel in trays or big fabric bags inside.
Is this sensible? The inside space is probably between 10 and 20 cubic metres at a guess, and is fairly well sealed except when I'm there. I can visit as often as necessary to swap the silica and dry it in the oven at home. I don't really know how much I'd need.
Any pointers to a cheap source of bulk silica gel?
Doubt it would work for long or even be effective unless you can completely seal up the cabin then it might work but you'd probably need to get the place cold and dry first.
I think your better bet is ventilation, being more or less sealed up means that any damp in there can't get out. Would a green house heater run long enough to warm the place enough but bear in mind burning paraffin or gas produces moisture...
Why "for long"? Surely it either works or it doesn't. Unless you mean the silica becoming saturated - the yard is approximately on my way home from work, so I could change it daily if necessary.
Well, it's reasonably well sealed. Everything except the main hatch is completely watertight, due to being a boat. The main hatch closes with tongue and groove boards that fit fairly tightly into a frame. Not watertight but not blowing a massive draught through either.
Yes, that's the problem. What it desperately needs is a good mains dehumidifier running 24/7 into a drain - that would dry it out beautifully. But unless such a thing can be run off a not-stupidly-huge solar panel or windmill, it's not possible. Not to mention the cost of said panel or windmill.
The problem at the moment is that the outside world is soaking wet too. And it's hard to see how to arrange natural ventilation that keeps the rain out, and is also reasonably secure (any idiot can walk into the yard).
I wouldn't use one of those. As you say, they produce moisture, and my mum's greenhouse was always noticeably clammy after she'd run the heater.
Not really, Silica Gel will absorb about 20% of its weight of water but the problem in a boat is not usually atmospheric moisture so much as condensation. During the day the boat heats up in the sun (if any!) and moisture is absorbed by the air, at night this moisture condenses out on the cold boat surfaces and makes things damp. They don't dry out thoroughly next day and the cycle repeats.
You might find a small solar panel and some low voltage fans to give some forced ventilation is a better solution as they remove the warmer and more moisture laden air during the day and minimise condensation.
You can buy marine solar vents, eg
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make your own using some computer fans, rechargeable battery and small PV panels. If you match the battery and the panel size no complicated electronics are needed.
Maybe a temporary hatch with one of those ventilation fans (as sometimes seen on the roof of buildings / vans) mounted in it? Those seem designed to spin when there's a breeze and suck air out, yet still be rain-proof.
I think anything running from solar panels / generator / windmill would be too prone to vandalism (aside from the expense).
Also, maybe something running from a car battery / timer*? With two batteries you could have one in use and one on standby at home, charging. That's still quite a few quid's worth of batteries, though. Dunno if viable 12V dehumidifiers exist!
or run it flat out, but I'm not sure a car battery would remain charged for long enough, and running them completely flat isn't a good idea.
I would not expect it to be all that effective in such a large space. It would need some air circulation and providing that circulation would mean ventilation - then you would be trying to dry the entire planet.
Maybe a daft idea, but how about a running collected cold rain water through something like a radiator (car or house radiator) and having that act as a condenser? Then you just need to collect the condensed moisture and pipe it out side. An powerless dehumidifier, the cabin is bound to be a little warmer than the outside, so should work if you can get at least some water flowing.
Maybe two such radiators back to back, one inside, one outside with a small 12v pump to circulate the same water continuously.
Another way might be to use an opened up 12v pelter fridge to collect the moisture, plus a 12v computer fan to stir the air and take the 12v batteries home to recharge.
TBH no. When used as a dessicant in a laboratory environment I'd be using about 400g of silica gel for a five litre container.
Umm, I doubt it, my boat has several vents. Most baots do. For the engine compartment which is not well sealed from the cabin, for the heads and also for the cabin itself. There's a damned big ventilator in the washboards.
Well, based on the above, about 800Kg of silica gel to do a decent job.
Silica gel would need sackfuls of it to deal with this sort of volume.
Another approach (as done with real gin palace motor yachts) is to cocoon the thing and stop any moist air getting into it from the outside. It won't keep it dry on its own, but it will hugely improve the performance of any dessicator you have inside there.
Cheers for all the suggestions. I can get six and a half kilos of silica (second hand from a lady who dries flowers with it) for £12, but it sounds like the consensus is not to bother. After I posted I did think of fitting a van vent to a plywood board replacing one of the hatches, but my dad (co-owner of the boat) reckons the air outside is just as damp as the boat at this time of year, so there's no point pulling it through. He's inclined to just leave it till the weather's warmer, since there's nothing especially perishable on board (fibreglass boat by the way, though a certain amount of interior wood).
My main reason for trying to dry things out is that a hatch above the engine bay is cracked and leaking (and has been for some time) and all the sound-absorbing foam is completely sodden. Once I've replaced the hatch I'd really like to get all this dry.
Yes, Andy, but calcium chloride soon becomes saturated and has to be dried to become effective again. It needs heat to dehydrate it and you can't do that inside the boat.
Calcium chloride would need more.
I've never seen any yacht cocooned. I've seen them with extractor fans powered by batteries - replaced/recharged frequently by mains or wind/ solar power..
For £12 I'd give it a try. The fact it has been used makes no difference, it will still work just the same. And that's a lot less than you would pay for it retail.
If you've got access to that sort of quantity, then go for it.
Remember to re-activate it immediately before use, and store it afterwards in tape-sealed Quality Street tins (hey, it's Christmas) until it's needed. In this weather, it doesn't take long to absorb its full capacity.
I'd also suggest a cheap hygrometer or two (TLC, under aircon fittings, else Lidl)
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