Proper Interior Humidity
- Thread starter Nodak7
- Start date
Humidity is not as critical as ventilation. The two are related of course but there is very little you can do to control the humidity that does not look like ventilation.
I would second the point that ventilation is key. We kept our boat in your area (Englewood) for almost 8 years and didn't have any problems. Occasionally, we wiped down the interior woodwork with Murphy's wood soap, or treated it with Old English furniture polish. The boat was used a lot, and the hatches were open on a daily basis. The only problem we had was with light mold on the interior after the boat was closed up and stored for the winter in New England.
I should add that we installed fans in the main cabin and the v-berth that greatly aided with ventilation.
I should add that we installed fans in the main cabin and the v-berth that greatly aided with ventilation.
I have a dehumidifier in the boat during the winter for the last few years and I have been keeping the humidity at 35-40% range with no mould and no splitting or wood damage however, this is only my guess from what is the comfort range at home. Would also like to know of other people's experiences.
In part I think it depends on where you keep the boat.
Here in Michigan where we have winter (and this year it's a doozy) and the boats are hauled I doubt any marina would let you keep a dehumidifier running, nor would you want to. Marinas see them and heaters as fire hazards on unattended boats. You'd have no way to empty the water and it would freeze anyway. For us getting through the fall until the temperatures drop is the critical period. Once the cold air gets here it's very dry anyway. So ventilation is the key.
Winter covers that breath, propping the cushions up and away from the hull so that air can move around them are key.
As to your question on humidity levels that's a bit trickier. Humidity is measured as relative humidity and this is temperature dependent. Most literature talks about minimum humidity levels in housing for human comfort. For that the recommendations from places like the national institute of health and ASHRAE talk about 30% to 50% relative humidity. These are cold temperature levels. On a 10 degree day if you had 50% RH you'd have water running down your windows. While on a 50 degree day it wouldn't be noticeable.
Here is a thought for you. The air conditioners that came with my boat have a couple of setting features on them. There is of course heating and air conditioning, but then there is a setting for humidity control. What it does is periodically cycle the air conditioners and run the fans to keep the cabin from getting stale and the humidity getting too high. I don't have the manuals right in front of me but I believe they are AirrrCool by Dometic. Perhaps check their web site to see what they have in the way of recommendations.
As an aside, I don't leave the dehumidification or air conditioning units running when we are not on the boat. While a cool non stuffy cabin is appealing, there are risks.
- there is a water circulating pump that runs as part of the air conditioning systems. If the intake were to clog with weeds the pump could starve and burn up. Or more significantly if a hose were to come loose, that pump moves a lot of water and it could fill the boat very quickly.
- as someone who's worked as an environmental professional my whole life, running an air conditioner on a poorly insulated unattended boat just seems wrong. Whether you believe in climate change or not, burning up electricity to keep an unattended boat comfortable wastes resources and costs the marina money which ultimately gets reflected back in the price of slip rental.
What I do have are a couple of those day / night mushroom fans mounted in the cabin top. They keep air moving day and night so that the air in the cabin stays equalized with the outside air.
Here in Michigan where we have winter (and this year it's a doozy) and the boats are hauled I doubt any marina would let you keep a dehumidifier running, nor would you want to. Marinas see them and heaters as fire hazards on unattended boats. You'd have no way to empty the water and it would freeze anyway. For us getting through the fall until the temperatures drop is the critical period. Once the cold air gets here it's very dry anyway. So ventilation is the key.
Winter covers that breath, propping the cushions up and away from the hull so that air can move around them are key.
As to your question on humidity levels that's a bit trickier. Humidity is measured as relative humidity and this is temperature dependent. Most literature talks about minimum humidity levels in housing for human comfort. For that the recommendations from places like the national institute of health and ASHRAE talk about 30% to 50% relative humidity. These are cold temperature levels. On a 10 degree day if you had 50% RH you'd have water running down your windows. While on a 50 degree day it wouldn't be noticeable.
Here is a thought for you. The air conditioners that came with my boat have a couple of setting features on them. There is of course heating and air conditioning, but then there is a setting for humidity control. What it does is periodically cycle the air conditioners and run the fans to keep the cabin from getting stale and the humidity getting too high. I don't have the manuals right in front of me but I believe they are AirrrCool by Dometic. Perhaps check their web site to see what they have in the way of recommendations.
As an aside, I don't leave the dehumidification or air conditioning units running when we are not on the boat. While a cool non stuffy cabin is appealing, there are risks.
- there is a water circulating pump that runs as part of the air conditioning systems. If the intake were to clog with weeds the pump could starve and burn up. Or more significantly if a hose were to come loose, that pump moves a lot of water and it could fill the boat very quickly.
- as someone who's worked as an environmental professional my whole life, running an air conditioner on a poorly insulated unattended boat just seems wrong. Whether you believe in climate change or not, burning up electricity to keep an unattended boat comfortable wastes resources and costs the marina money which ultimately gets reflected back in the price of slip rental.
What I do have are a couple of those day / night mushroom fans mounted in the cabin top. They keep air moving day and night so that the air in the cabin stays equalized with the outside air.
I have a dehumidifier running in my boat, with the drain going into the bilge. I usually leave it set on 55 per cent humidity. Down here, any lower than that, and the humidifier will never cut off.
Without it, I get mildew in a few weeks. A lot of guys leave their A/C's on, but I'm always afraid of a hose blowing and sinking the boat before anyone notices.
Without it, I get mildew in a few weeks. A lot of guys leave their A/C's on, but I'm always afraid of a hose blowing and sinking the boat before anyone notices.
Our H410 has built in dehumidifier. I have been tempted to leave it running for extended periods. The marina is on Hornby Island which off Vancouver Island and there is lots of rain and humidity in the winter months although it seldom freezes. There is an uncertainty about shore power in winter. I currently leave an small space heater on low which moves air and supplies minimal heat. I don't like to leave on power as this makes me nervous even though a fellow sailor regularity checks the boat. It is difficult for me to make regular checks as it is a 1400 km drive to the boat. Question, has anyone installed a sensor or timer to regulate the dehumidifier's run time? Is that even a feasible alternative ?
Quadrille 38 had good points. Let me expand on a few.
Humidity levels and condensation. This depends both on the temperature AND on the amount of insulation. With double glazed windows (I put them up in the winter) and a cored hull, the humidity can be a little higher than other wise, but 40% (warm boat) is probably the upper limit in sub-freezing weather. Consider the least insulated portion of the boat; if there is solid glass somewhere, that is where the drip will start. I have a hygrometer at the nav station. Bear in mind that relative humidity is very temperature dependent; in the winter the relative humidity may be 65% at ambient temperature, but when I turn the heat on it will drop to 35% as the boat warms. So long as the ambient temperature humidity RH is <70% you'll be fine.
Humidity and wood. You can browse conservation sites. Generally they will talk about staying below 70% and stability (up and down is bad).
Ventilation is certainly not the only way or the most effective. In the north country, when the air warms but the water is still cold (or snow on deck) the boat is going to drip no matter how much you ventilate because the hull is colder than the air. While leaving the AC on presents several risks, leaving a small thermo electric dehumidifier on, draining into the sink, is low risk. If the sink drain is below the water line, perhaps snaking a small hose out in the to cockpit will work. My boat is quite fresh since I started this.
http://sail-delmarva.blogspot.com/2012/12/dehumidifier-vs-desicant.html
Run time? My answer is to use a very small dehumidifier and to have it on a time. It runs about 6 hours each day (at night when the RH is highest and so it can defrost during the heat of the day), providing a nice long defrost cycle. Since they are more effective in damp air, that makes it, to some extent, self regulating.
Humidity levels and condensation. This depends both on the temperature AND on the amount of insulation. With double glazed windows (I put them up in the winter) and a cored hull, the humidity can be a little higher than other wise, but 40% (warm boat) is probably the upper limit in sub-freezing weather. Consider the least insulated portion of the boat; if there is solid glass somewhere, that is where the drip will start. I have a hygrometer at the nav station. Bear in mind that relative humidity is very temperature dependent; in the winter the relative humidity may be 65% at ambient temperature, but when I turn the heat on it will drop to 35% as the boat warms. So long as the ambient temperature humidity RH is <70% you'll be fine.
Humidity and wood. You can browse conservation sites. Generally they will talk about staying below 70% and stability (up and down is bad).
Ventilation is certainly not the only way or the most effective. In the north country, when the air warms but the water is still cold (or snow on deck) the boat is going to drip no matter how much you ventilate because the hull is colder than the air. While leaving the AC on presents several risks, leaving a small thermo electric dehumidifier on, draining into the sink, is low risk. If the sink drain is below the water line, perhaps snaking a small hose out in the to cockpit will work. My boat is quite fresh since I started this.
http://sail-delmarva.blogspot.com/2012/12/dehumidifier-vs-desicant.html
Run time? My answer is to use a very small dehumidifier and to have it on a time. It runs about 6 hours each day (at night when the RH is highest and so it can defrost during the heat of the day), providing a nice long defrost cycle. Since they are more effective in damp air, that makes it, to some extent, self regulating.
Keep my 27' Catalina year-round in the water in Vancouver, BC. I get very bad condensation and moisture problems if not managed. I use a small space heater set on low, and a dessicant dehumidifier from EvaDry:
http://www.eva-dry.com/products/edv-4000-rotary-desiccant-dehumidifier/
This machine is amazing. Light, quiet, efficient, pulls 7L per day, and works down to 34degF. I run the continuous drain into my sink. Since running this setup this winter, even paper left inside the boat is crisp. She is much fresher (and healthier) all around. I am comfortable doing this since rewiring shore power last summer, with good breakers and GFI outlets. I considered running it into the bilge, as there is part of me that is nervous leaving the sink seacock open, but it seemed counter productive to use all that energy to pull water out of the air, only to leave it in a standing pool in the bilge. I check the boat at least once a week, and have no problems at all so far.
http://www.eva-dry.com/products/edv-4000-rotary-desiccant-dehumidifier/
This machine is amazing. Light, quiet, efficient, pulls 7L per day, and works down to 34degF. I run the continuous drain into my sink. Since running this setup this winter, even paper left inside the boat is crisp. She is much fresher (and healthier) all around. I am comfortable doing this since rewiring shore power last summer, with good breakers and GFI outlets. I considered running it into the bilge, as there is part of me that is nervous leaving the sink seacock open, but it seemed counter productive to use all that energy to pull water out of the air, only to leave it in a standing pool in the bilge. I check the boat at least once a week, and have no problems at all so far.
Hygrometer/thermometer
I have a comfort meter, and if its good for my comfort, then its probably good for the boat. I also run a dehumidifier and have to empty it every couple of days during the rainy periods in the winter (live on the wet coast too). Since I started doing this the boat stays dry, smells better and no mould. I only apply heat when the temps get a ways below zero. Mind you when its get really cold the humidity drops way down anyway.
I have a comfort meter, and if its good for my comfort, then its probably good for the boat. I also run a dehumidifier and have to empty it every couple of days during the rainy periods in the winter (live on the wet coast too). Since I started doing this the boat stays dry, smells better and no mould. I only apply heat when the temps get a ways below zero. Mind you when its get really cold the humidity drops way down anyway.
Attachments
I also run a dehumidifier in the winter. I am on the boat every week to two weeks. I find when I first start using in the fall, there are gallons of water that come out of the wood, cushions, etc. After it has been running in the closed up boat for a couple of weeks, the amount extracted is drastically reduced to less than a gallon a week. I set it at the low setting and on the lowest lever of humidity, which is about 30%. The amount of power used is less than running a small heater so I think this is a safer way of taking care of the humidity. I tried everything from dessicants to small heaters. The last attempt was to just leave a hatch open. This worked better than using any interior heat but still had mildew issues. Since using the dehumidifier for the past four winter seasons, no mold, mildew, or any other humidity issues. The interior of the boat also heats up much faster with less moisture mass to heat in the air and the interior surfaces. If you have shore power, dehumidifier is by far the best way to go.
Reduce humidity
I have a 2000 Hunter 410 on the Great Lakes. It's on the hard in the winter. I have 12 old damp rid basket containers spread throughout the interior. I also have 3 plastic colanders in two head sinks and one in the galley sink. I purchase Calcium Chloride at the local feed store. 50 lb. / $13. It's cheap and I use lots of it. It keeps the interior dry while on the hard. It doesn't work well below freezing. It works best in the shoulder season when most mold develops. I'm also starting to use Kanberra Gel (Tea Tree Oil) too.
I have a 2000 Hunter 410 on the Great Lakes. It's on the hard in the winter. I have 12 old damp rid basket containers spread throughout the interior. I also have 3 plastic colanders in two head sinks and one in the galley sink. I purchase Calcium Chloride at the local feed store. 50 lb. / $13. It's cheap and I use lots of it. It keeps the interior dry while on the hard. It doesn't work well below freezing. It works best in the shoulder season when most mold develops. I'm also starting to use Kanberra Gel (Tea Tree Oil) too.
Pain
Those damp rid plastic containers are a pain and found that my AC humid setting works pretty good plus I have a few fans moving air around is real good and a solar venting in veeberth.
Nick
Those damp rid plastic containers are a pain and found that my AC humid setting works pretty good plus I have a few fans moving air around is real good and a solar venting in veeberth.
Nick
Thanks to the info in this forum, particularly the post by Joidevivre, I recently purchased this dehumidifier for our H37C: https://www.eva-dry.com/dehumidifiers/edv-4000-rotary-desiccant-dehumidifier/
Only been running a couple days now, but via my remote temperature/humidity sensor, RH has settled in around 50-55%. This is on the Automatic setting, which the manual says will maintain an RH in the 50s. It also has a "low" and "high" setting... haven't experimented much with those. It doesn't have an option to set a specific RH, and I'd kinda like it to be more like 35-40%. Maybe I'll try leaving it on "low" and see what it does.
I have it set up with the optional drain pipe connection, currently just running into the bilge.
Prior to setting up this dehumidifier, I was seeing RH regularly in the 70s.
Now I'm thinking of ways to automatically pump out the "nuisance water" in the bilge. Normal bilge pump gets it down to under an inch, but still that is a lot of water to potentially evaporate back into the boat. Thinking of a small diaphragm pump on a timer that would run once a day..
Tom
Only been running a couple days now, but via my remote temperature/humidity sensor, RH has settled in around 50-55%. This is on the Automatic setting, which the manual says will maintain an RH in the 50s. It also has a "low" and "high" setting... haven't experimented much with those. It doesn't have an option to set a specific RH, and I'd kinda like it to be more like 35-40%. Maybe I'll try leaving it on "low" and see what it does.
I have it set up with the optional drain pipe connection, currently just running into the bilge.
Prior to setting up this dehumidifier, I was seeing RH regularly in the 70s.
Now I'm thinking of ways to automatically pump out the "nuisance water" in the bilge. Normal bilge pump gets it down to under an inch, but still that is a lot of water to potentially evaporate back into the boat. Thinking of a small diaphragm pump on a timer that would run once a day..
Tom
I put my dehumidifier in the sink and have a hole drilled in the catch basin. Only down side is I have to keep the sink thru-hull open
Our weather in San Diego isn't as severe. I'm able to keep a couple of the small hatches cracked under the Bimini and I keep an 10" electric fan plugged in 24/7 to move the air. I leave the fan on the cabin floor up in the bow pointed aft. Works great.
Many will scoff at me, but I'm a ventilation contrarian. 
In my specific case. Might be different for other boats.
I seal the boat. Open hatches will let more moisture in. I place 3 Damprid tubs, one in the V, one in the salon, one in the quarter berth. Then I place a West Marine warmer in the middle. WM calls it a dehumidifier but it's really a condensation inhibitor. However, it also acts as an air circulator, delivering moisture to the tubs.
Also keep the icebox and bilge DRY. Drain and towel the icebox, and pump the bilge (if needed). This eliminates a moisture source.
Boat is always dry. I'm in So Cal now but had the same results in Annapolis.
Empty the tubs every 2 weeks or so, or when about an inch of water is present.
Buy the tubs, then reuse them by getting bulk bags for about $4 at Home Depot. One bulk bag will fill 9 tubs, or my 3 tubs 3 times. Cost and buy frequency are negligible, and the tubs live where they are in the cabinets, so don't have to monkey with them except to empty water and replenish the desiccant.
In my specific case. Might be different for other boats.
I seal the boat. Open hatches will let more moisture in. I place 3 Damprid tubs, one in the V, one in the salon, one in the quarter berth. Then I place a West Marine warmer in the middle. WM calls it a dehumidifier but it's really a condensation inhibitor. However, it also acts as an air circulator, delivering moisture to the tubs.
Also keep the icebox and bilge DRY. Drain and towel the icebox, and pump the bilge (if needed). This eliminates a moisture source.
Boat is always dry. I'm in So Cal now but had the same results in Annapolis.
Empty the tubs every 2 weeks or so, or when about an inch of water is present.
Buy the tubs, then reuse them by getting bulk bags for about $4 at Home Depot. One bulk bag will fill 9 tubs, or my 3 tubs 3 times. Cost and buy frequency are negligible, and the tubs live where they are in the cabinets, so don't have to monkey with them except to empty water and replenish the desiccant.
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I have shore power....so the AC stays in away/dehumid when we are away. It runs the system 6 times a day for 1 hour or 1 degree reduction. Boat stays clean. Yes, I am up north.....but we still get much humidity. Would this work inFL? not sure.