How dry is too dry? - Page 2 - SailNet Community
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post #11 of 24 Old 10-10-2008 Thread Starter
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Originally Posted by jrd22 View Post
Faster- when you get the boat to 30% RH, would you let me know? I want to move into it as I'm getting a little moldy and mildewy myself lately. Thanks, I knew you would understand.

John
Sure John... we can meet at Roche Harbor and we'll do the swap

Ron

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post #12 of 24 Old 10-10-2008
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A dry boat is a happy boat. I dont think your really in danger of harming anything when you use a dehumidifier. Are you a liveaboard?

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post #13 of 24 Old 10-10-2008 Thread Starter
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A dry boat is a happy boat. I dont think your really in danger of harming anything when you use a dehumidifier. Are you a liveaboard?

-Spencer
Not a liveaboard.. so that's why the "comfort" aspect (eg 50-60%RH) is not a concern.. We have dorade vents for ventilation, so as Cameron mentioned there's going to be a limit to how dry things will get, so I think we're OK to run it full time. It's already made a difference to the normal off season feel of the boat so we're pleased at this point.

Thanks everyone.

Ron

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post #14 of 24 Old 10-10-2008
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Too dry is when the water level gets below 5 feet and my keel drags!

Don
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post #15 of 24 Old 10-10-2008
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Our J boat gets very wet inside when racing in the rain and dousing chute, changing sails etc. Another boat I sail on - Peterson 37 has dehumidifier plugegdin when not sailing. I plan to do same next summer to dry out boat between sailing and then move to dock box when sailing. This just to dry out boat from rain ....

What are those West Marine devices earlier in this thread?

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post #16 of 24 Old 10-11-2008
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Faster,
One concern you will have at lower levels of humidity can be any wet cell batteries on board. If you keep the humidity artificially low, and 30% is pretty low-depending upon the temperature, you can slowly evaporate the water out of any wet cell batteries. This is a problem often observed when continuously storing batteries in an A/C environment as well.
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post #17 of 24 Old 10-11-2008 Thread Starter
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Faster,
One concern you will have at lower levels of humidity can be any wet cell batteries on board. If you keep the humidity artificially low, and 30% is pretty low-depending upon the temperature, you can slowly evaporate the water out of any wet cell batteries. This is a problem often observed when continuously storing batteries in an A/C environment as well.
Excellent point, Sway! Will keep a closer eye on the battery banks. Thanks much.

Ron

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post #18 of 24 Old 10-11-2008
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Moisture cycling is hard on wood, joints, and veneers, but I dunno how big a problem that might be in this case. As wood swells and shrinks due to MC, it can undergo checking or delamination; drawers and doors may stick; and glue joints can fail. Hardware can come loose as it is levered out, and contact seals may lose weathertightness. Thirty percent minimum RH isn't all that awful, but much depends on your maximum RH relative to that and, crucially, length of each cycle. Wood absorbs and loses moisture slowly, often lagging several months behind ambient conditions.

The only sure way to monitor things is by measuring the internal MC of wood and panel products directly. If you expect, later, the boat interior to spend long periods at 90% humidity, I'd advise no lower than 50% to 60% now. The rate of loss or absorption increases with gradient, as does the potential for damage. If even your wet season is down around 70% RH, you can prolly dehumidify it to 30-35%.

I always give my hardwood at least a month to shake down before milling and joining it, as it may come from states at 80% humidity and Wyoming is currently running ... 17%, according to the meter on the wall. That can represent 6 points internal moisture content in wood products, or roughly 1/4" of shrinkage across a 12" maple board (flatsawn). Yikes!

One last concern: dehumidifiers drawn tons of power, as they are just reefers turned inside out and they cycle constantly. Older ones were pretty solid, but new Box Store units burn up with depressing frequency. Me mum goes thru one every eighteen months in her basement. When the compressors do kick it, they can drawn a mighty surge of amps. Make sure your power cord is sized for 'angry motor having meltdown.'

Buccaneer18, Grainnia
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Last edited by bobmcgov; 10-12-2008 at 10:34 PM.
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post #19 of 24 Old 10-11-2008
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Faster, IIRC the USN standard aboard nuclear submarines is still the same 74F 45%RHI that they set when they first started looking into how to keep crews sealed up for 90 days at a clip. That's partly from a comfort level, i.e. so you can be in shirtsleeves and still feel awake not cold.

I'm not sure how much I'd trust an RHI meter on a boat, after all, there's gobs of sea breeze drifting in all the time--unless you're on one of those 90-day tours. 40-45% should keep everyone including the boat happy, but if you like it a little drier...I can't see that would hurt. See what kind of compromise you can strike with your heater as it gets colder.
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post #20 of 24 Old 10-11-2008
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isn't there is a huge storage facility for aircraft in the desert where the humidity stays around 10 %? also in furniture building you want your wood well below that level even so I fail to see how this would hurt a thing..Ill gander a guess that the wood used in boat construction is below 7% moisture content..IMHO

Edit; Bob sounds like your a wood worker too..any tricks on stabilizing Madrona.

Last edited by Stillraining; 10-11-2008 at 08:03 PM.
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