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Humidity levels in your boat


Grassman

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A boater friend has a dehumidifier. She lives on board and is marina based. She reckons she used to get a lot of condensation but much less so now, and that it collects about 2 litres of water a day. Her stove is bust so she heats the boat using either the central heating or oil filled electric radiators (she is hooked into landline).

 

She thinks it's brilliant but since she bought a humidity meter she has become obsessed with the humidity reading and won't turn it off until it gets to 40% which I think could be so low it would make the air far too dry.

 

I'm trying to discourage her from being so obsessive and have told her to get rid of the meter but she won't,  so does anybody on here have a similar set up and if so what is the lower percentage level you usually aim for?

 

Gawd knows what she spends on electricity and I've told her it would be better to buy a new stove as this would do the same job and massively lower her electricity spend.

 

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At present my boat temp in front cabin is 25.4 degrees and humidity is shown as 40%. I never look at the humidity reading but did after reading your post. We are cooking at present and the solid fuel squirrell is lit. No idea about what humidity is generaly?

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All the reading I have done on the subject indicates that the optimum relative humidity in a dwelling is around 40%. I use a dehumidifier on my (winterised) boat and set it to 50% RH, but that is just to keep mould at bay.

Edited by Paladine
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I do have a dehumidifier.

I have it on the middle setting which should mean it cuts out at 50%humidity.  The instructions for the dehumidifier say 50% should be okay (see link below) .

The boat feels very dry and comfortable.

https://www.meaco.com/pdfs/Meaco DD8L Dehumidifier instruction manual_July_2015.pdf

 

.

 

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6 hours ago, Paladine said:

All the reading I have done on the subject indicates that the optimum relative humidity in a dwelling is around 40%. I use a dehumidifier on my (winterised) boat and set it to 50% RH, but that is just to keep mould at bay.

 

2 hours ago, MartynG said:

I do have a dehumidifier.

I have it on the middle setting which should mean it cuts out at 50%humidity.  The instructions for the dehumidifier say 50% should be okay (see link below) .

The boat feels very dry and comfortable.

https://www.meaco.com/pdfs/Meaco DD8L Dehumidifier instruction manual_July_2015.pdf

 

Same with me, usually only for mooring (when at home during winter) - to stop dampness in soft furnishings and condensation on windows - set at 50% or thereabouts. Anything lower is unnecessary - it just consumes more power for no real benefit.

 

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On 24/01/2019 at 18:10, Grassman said:

 

A boater friend has a dehumidifier. She lives on board and is marina based. She reckons she used to get a lot of condensation but much less so now, and that it collects about 2 litres of water a day. Her stove is bust so she heats the boat using either the central heating or oil filled electric radiators (she is hooked into landline).

 

She thinks it's brilliant but since she bought a humidity meter she has become obsessed with the humidity reading and won't turn it off until it gets to 40% which I think could be so low it would make the air far too dry.

 

I'm trying to discourage her from being so obsessive and have told her to get rid of the meter but she won't,  so does anybody on here have a similar set up and if so what is the lower percentage level you usually aim for?

 

Gawd knows what she spends on electricity and I've told her it would be better to buy a new stove as this would do the same job and massively lower her electricity spend.

 

I have a temp/humidity meter, but no dehumidifier as condensation is never a problem in my boat. Right now it's reading 36% and I've just been cooking right next to it, boiling up some veg. I think the highest I've ever seen it in the 10 or so years it's been in the boat might be about 47%?

 

I don't really know why some boats need dehumidifiers and others don't. Lack of good ventilation on the former perhaps.

IMG_20190125_191132_6.jpg

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11 minutes ago, Cheshire cat said:

I wonder if it is working properly?

Yes it is. I calibrated it against a more sophisticated model at a research centre I was working at a few years ago. It may have gone out of sync since then I suppose, but I still see the same sorts of temperatures and humidities so I don't see why it would have. I never get any condensation in my boat apart from a bit on the portholes, so why do you think it might be wrong? 

 

Edit: Could it be that the larger internal volume of a widebeam like mine is less prone to humidity and condensation than the much smaller volume inside a narrow boat? More air to absorb the water vapour created by people breathing, cooking, etc. A smaller surface area to volume ratio...

Edited by blackrose
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Wow - some of you have really low humidity readings. I thought 55% was about ok but mine can easily get up to 70 or80%+ usually if drying laundry inside. No wonder my boat is all mouldy :(

A thing I heard was that actually when the air outside is cold and damp, it's better to keep windows closed otherwise all you are doing is bringing in more and more moist air.

Certainly the stove is good at dispelling moisture, though of course by its very nature it must be drawing new air into the boat (through the vents).

I do very little boiling or frying - everything goes in the oven if possible.

Mr Smelly - 25.4!? Are you trying for a sauna?

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1 hour ago, Johny London said:

Wow - some of you have really low humidity readings. I thought 55% was about ok but mine can easily get up to 70 or80%+ usually if drying laundry inside. No wonder my boat is all mouldy :(

A thing I heard was that actually when the air outside is cold and damp, it's better to keep windows closed otherwise all you are doing is bringing in more and more moist air.

Certainly the stove is good at dispelling moisture, though of course by its very nature it must be drawing new air into the boat (through the vents).

I do very little boiling or frying - everything goes in the oven if possible.

Mr Smelly - 25.4!? Are you trying for a sauna?

Heres one from a couple of nights ago ? We dont DO cold, no way are we living in one of those freezing house things people live in. We put coats on when we visit relatives houses!!

IMG_20190123_104106.jpg

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On a technical point, the RH is affected by the air temperature and pressure.

As warm air can hold more water vapour than cold air, an increase in temperature will cause the RH to drop.

So bringing in cold air from outside and warming it up means the air becomes drier.

Things will dry out when water evaporates thus raising the RH.

Then when it cools down (eg, heat off), the RH drops, when and at the actual dewpoint (100%RH) the vapour condenses (seen as water on cold windows) but also permeates soft fabrics making them feel damp.

 

 

 

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