Dehumidifier water into bilge? Advice please

[AuntyRinum]

I posted a question about dehumidifiers elsewhere and got the suggestion that I get a dehumidifier with a drain rather than one which you empty.
If I drain that into the bilge of my Hillyard which always has salt water in it, do you think that the fresh water from the dehumidifier will be sufficiently mixed with salt water not to be a problem?

 

[lackey]

Re: Dehumidifier water into bilge? Advice please

If there's any doubt, do what they do on the Great Lakes and tip a bag of salt into the bilge.

 

[ChrisE]

Re: Dehumidifier water into bilge? Advice please

Have you thought about leading the water out of the sink drain and thus outside of the boat? That's what most people I know do.

 

[Mirelle]

Dehumidifier water into bilge? Very bad idea, I think.

There are several things that I think are wrong with this notion.

First, the water will evaporate from the bilge and get re-cycled!

Second, you really don't want a trickle of fresh water in your bilges - causes rot and may smell foul as well.

Third, I really do not think that dehumidifers are a good idea on wooden boats. Good ventilation is a much better (and cheaper!) plan.

The dehumidifier, if it is working properly, will seek to bring the moisture content of the abmient air to a level at which the timbers in the boat are being dried out to below their natural moisture content. This you do not want, as they will warp and crack. If the moisture content is in the teens of percent you will be OK - rot needs about 21% - and the dehumidifier will be trying to get it down to zero.

If a wooden boat smells musty and fusty when you open the hatch, two things are probably wrong. First, she almost certainly has a deck leak somewhere - find it and fix it - and second she has inadequate ventilation when not under way - improve it.

We keep down pillows and duvets along withbooks andso on aboard our elderly wooden boat and they stay perfectly dry and fresh, as do books, etc., all season.

 

[Gordonmc]

Spending an inordinate amount of time and effort trying to keep fresh water out of my Hillyard I would naturally dissuade you from draining your dehumidifier into the bilges. There is always an inch or two of brine in the lowest part of the bilge of my 8 tonner, but that only amounts to a couple of strokes of the pump, maybe three or four litres maximum. A dehumidifier can such that amount from the air in one warm day which means for a weak solution.
Although I respect Mirelle's point of view I believe there is a place for a dehumidifier on a wooden boat. I had one running every time there was a frost risk last winter and it was pleasant turning up for a weekend out in January and February without the coachroof ceiling dripping with condensation. The B&Q bought dehumidifier sat on a galley unit and drained into the sink.
The reality is that on a very cold, still day condensation is inevitable when the cabin temperature is the same as the sea (or near enough) and the outside temp is 5 to 10 degrees colder.
I only ran the dehumidifier on the coldest days and agree that, generally, ventilation is a better route and in that I now rely as the boat is away from a pontoon.
One tip...5" plastic plantpots fit nicely into the open front portholes of a Hilly. The drain holes in the pots allow air in but keep beasties out.

 

[Mirelle]

a question

Gordon - was FLAP under a winter cover?

I haven't had condensation problems like that inside the cabin, but I have had condensation on the inside of the winter cover, due to the conditions you describe.

That was a heavy PVC (truck tarpaulin material) winter cover - we are getting a new woven cloth one for this winter.

 

[AuntyRinum]

Thank you to everyone who replied to this.
I spend a great deal of my time on the boat and when I'm not travelling with my work, I live aboard.
It's a Hillyard 12 Tonner and is kept heated during the winter and condensation has not been a problem. Ventilation is very good with a constant airflow through the boat.
In spite of all that, the humidity inside is always high compared with the humidity outside e.g today it's 72% inside the boat and 46% outside. At night it is sometimes up to 90%.
I want to reduce the humidity mainly for health reasons, although I'm not sure what is an unhealthy upper limit.
The sink drain idea seems to be the right approach and also not to run it all the time to avoid the boat drying out too much.

 

[tillergirl]

Re: Dehumidifier water into bilge? Advice please

I think I'm with Mirelle on this in terms of a laid up vessel. I only get condensation inside under the cover at the very beginning of the winter when the cover first goes on; then the flow of air underneath the cover - all hatches open, all lockers open etc gets rid of it. However, the extra moisture I would say that comes from living aboard and could be tackled with a dehumidifier. If you can measure it, it seems to me you can control how 'wet' it is inside. What the 'right' level should be is an interesting question? but Mirelle is certainly right that if you drain it into the bilge, you're recycling it. Sink seems to be the answer.

 

[DRW]

We have got a small dehumidifier. It has a humidity switch, similar in principle to a heater thermostat, so it just does it's own business of going on and off as it needs once set. If you are living on board, then the integral bucket would probably be large enough for a couple of days running.

90% humidity has just got to be bad for anything on board, including you and the boat. I wonder what type of heating you have for her as it sounds almost like gas without a flue, which has other health hazards apart from the humidity it creates. If it is gas heating, perhaps a move to something else would help?

Regards, David.

 

[AuntyRinum]

Heating is an Eberspacher. My mind is made up. I'll get a dehumidifier discharging into the sink with a sensor as you suggest.

 

[Gordonmc]

Re: a question

Hi,

The boat was sailed throughout last winter, so there was no overall cover for the cabin. Just a cockpit cover and one for the forward end of the coachroof and forehatch. Anything more would dissuade me from using the boat.
This winter the boat is on a mooring so I will use an over-all cover which can stay on as the sails will come off anyway. I am on the lookout for a suitable heavy tarp.

 

[tcm]

Hi. The dehum won't do very much if there is "lots of ventilation" (the dehum needs to dehumidify a fixed boatful of air - it won't be very effective if you ventilate as well)

The air is not uniformly humid in all areas of the boat. The dehum needs to be low down in the boat- so sending water down the sink means it will have to be on a galley worksurface which isn't as effective as into (say) a shower tray. The damper heavier air is low down. Look on some boats and you can see how (some) non-marinised fittings eg lower hinges on galley doors are pitted/rusty whereas (say) ceiling lights are always rust-free.

I would be surprised if the boat is naturally *very* well ventilated and the variance in your readings show that this isn't the case. One solution whilst living aboard would be a fan vent/pipe blowing air up from the bilges up outside to remove the heaviest dankest air. You could rig something temporarily to see how this would work.

 

[AuntyRinum]

"I would be surprised if the boat is naturally *very* well ventilated"

It is! Until I get new side windows fitted the wind will continue to whistle through the gaps at a steady rate.
Thanks for your advice which I have noted. I think I've got the answer now. Thanks to you and to all for your help.
An afterthought: Could it be the water evaporating from the bilge which is creating the humidity in this hot weather?

 

[tcm]

erm well yes it *might* be the water in the bilge, tho the hotter summer air can carry more water anyway and if you are in the marina or at sea there'll be a large blue wet thing outside that supplies a lot more water for humidity, i would have thought.

 

[AuntyRinum]

Thank you but, as I said, 72% inside the boat and 46% outside.
I think I'll open all the hatches now and get a humidifier for the winter and that should suffice.