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Discussion Starter #1
Hi All,

After the introduction to "rain in the boat" a few weeks ago, we purchased a marine stainless steel dehumidifier, which works well. It has a "mechanical" humidistat that has a % humidity scale on the dial...

Getting the machine to actualy get the humidity to a level we want will require a semi accurate hygrometer. We have tried all the $15 cheapos, none of which convinse me they're correct.

What do you use for a hygrometer in your boat?

Dave
 

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We have one of those (inexpensive) 'weather sets' with a clock, an analog barometer and temp and humidity gauge. Works well for us, and the indicated RH is pretty close to what our dehumidifier is set to (50%)
 

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Cheap weather station like Faster, as a bonus mine has an atomic clock, good for hitting the start line at the right time.
 

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What degree of accuracy are you seeking in a hygrometer and why?

Relative humidity is constantly changing with both the absolute amount of water vapor inside your boat and the air temperature as it changes minute-by-minute during the course of a day. So you are trying to hit a moving target. IMO, what you really want to achieve is an upper relative humidity limit range, say 40-50%. If the RH exceeds 50% for a bit, there is no harm done. The built-in humidistat on your dehumidifier is probably more than sufficient. And the cheapo hygrometers (your $15 units are overpriced by about 100%) are also plenty accurate.
 

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Discussion Starter #5
Maybe just the annal side of me. The humdistat in the dehumidifier (a mechanical one) is old. The "el cheapo" hygrometers all read something different, sometimes different from each other by %15 (have 3 of them). I agree perhaps, that a ballpark is good enough. A diesel engine without a tachometer might be good enough for some also.

My experience with wood... 40-50% is a tad on the low side, 60% is my target. My entire interior is solid teak, no plwood or veneers and have some pretty nice joinery. Some thick, some thin. Just trying to be careful, as our winters here in the Pacific NW are very damp... for months on end.
 

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My experience with wood and mold:

I have a collection of very nice, "solid wood" (i.e. not plywood) guitars. I aim for about 50% RH, but I haven't had any problems down into the mid-30s. Teak may behave differently than spruce, mahogany, and rosewood.

On the high RH side, I experience mold growth at 60% RH and higher. So I dehumidify to 45%.

You can check the calibration of your hygrometers. Search the web for "hygrometer salt test."
 

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Discussion Starter #7
My experience with wood and mold:

I have a collection of very nice, "solid wood" (i.e. not plywood) guitars. I aim for about 50% RH, but I haven't had any problems down into the mid-30s. Teak may behave differently than spruce, mahogany, and rosewood.

On the high RH side, I experience mold growth at 60% RH and higher. So I dehumidify to 45%.

You can check the calibration of your hygrometers. Search the web for "hygrometer salt test."
That's cool. I build guitars... clasical and acoustic (order all my solid wood directly from cutters around the world). My wood stays in a controled environment of 45-60% RH, 60-70 degrees F, electronically controlled with a household system. All the big manufacturers don't recomend going below 45%.

Don't want to hi-jack my own thread with guitar talk. :)

I've read here on the forum lots of folks don't go below 60% with their teak.
I've read about the salt test and will try that on a hygrometer that is adjustable. Thanks.
 

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When we first started using a dehumidifier I left it on constant cycle for a week... my wooden sliding doors fell out of their tracks! :eek:

Quickly settled on a 50% RH target, it's been terrific, paper is crisp, no mold or mildew anywhere below, even during our extended wet fall/winters here in BC. I'm a believer, but I'm not sure there's a 'critical' point.. keeping the boat between 50-60% simply has to be better than sitting cool at the natural 90-95% we can get during this time of year.
 

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dave, $10 temperature and humidity LCD combo from WalMart. Offhand, the spec that is right in the instruction sheet in the box said something like +-2F and 5%RH and that's about all you're going to get unless you pay for lab grade instruments.

"Good enough for government work" and only ten bucks.
 

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Makes me think of the irony that I'm presently trying to bring the humidity in the house UP from 25% to 60% this time of year.

On the boat, our dehumidifier just runs on a timed cycle. I think it runs about 20 mins every 90 mins, whether it needs to or not. I think having a timer and finding the right balance is probably the way to go. Circulation aboard is not terribly good, so knowing the humidity at the instrument may be very different from all the nooks and crannies and may change the moment the dehumidifier goes off.
 

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Makes me think of the irony that I'm presently trying to bring the humidity in the house UP from 25% to 60% this time of year.

On the boat, our dehumidifier just runs on a timed cycle. I think it runs about 20 mins every 90 mins, whether it needs to or not. I think having a timer and finding the right balance is probably the way to go. Circulation aboard is not terribly good, so knowing the humidity at the instrument may be very different from all the nooks and crannies and may change the moment the dehumidifier goes off.

Good point.. we leave all our lockers and doors open to try to maximise the exposure and coverage of the Dehu, but indeed it's a central device with probably limited reach. We have, in the past, set up muffin fans here and there to move air around too - that helps even without a dehumidifier.
 

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If you really want to be anal about it, get a sling psychrometer. But I agree that 40-50% is a good target range, and trying to achieve anything less than a 10-15% variation in a boat cabin is an exercise in futility.
 
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