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Winter Moisture Control

22K views 104 replies 31 participants last post by  Andrew65 
#1 ·
I'm transitioning to livingaboard my boat come April, however, I'm trying to troubleshoot as many problems as I can before I move on. Since the winter is coming to the Mid-Atlantic soon, my major concern at the moment is moisture and condensation. I know all about dew point and all that fun stuff, but what I would really like to know is: What are the most effective ways you all have found to help control moisture aboard? Any and all suggestions and advice are welcome!
 
#4 ·
*"HyperVent" from Defender, or equivalent, under bunks and settee cushions.

*If you're on shore power, a home-size dehumidifier from Home Depot or Lowe's, plumbed to drain directly to the bilge.

*Reflectix (silver bubble wrap stuff) lining the worst offender lockers

*Wipe cabin top and other mold-prone surfaces with a mix of white vinegar and water. We've heard good reports of tea-tree oil, gonna try that this winter as well.

*Tempting as it is to make soup or pasta for dinner every night, be conscious of meals that put excess moisture into the cabin. Or use pressure cooker.

*Rum! (Doesn't help the humidity but helps you keep it in perspective)
 
#6 ·
Ugh, when Sandy roared through I got absolutely whacked with condensation. The worst I've experienced so far.

I already had Hypervent under my cushions, and I've been running the electric, oil-filled heater. I ran out and bought the foil-backed insulation today, and I've already cut panels for the windows, hatches and the gaping maw of an anchor chain locker that is wide-open to the V-berth.

I need to build a wooden hatch cover for the anchor chain locker, and then put the insulation panel on top of that.

I fear that the only real way I'm going to get control of this situation is a dehumidifier. I really don't want another electrical load, another appliance to trip over... sigh.

One of those dry, autumn days would sure help dry out the boat after this storm.:rolleyes:
 
#8 ·
Thanks all for the advise! I'm glad I get a chance to "test run" a winter before moving on. It gives me some chance for trial and error. Nice to hear from people in the region!
Bubblehead, I have been putting up the reflectix all over the boat... hope it really does work. I also have a large opening where my anchor chain is, bungied a piece of tarp over it for Sandy, worked ok. Need to get a new cap for it. I figure, after going through Sandy I should have a good baseline for the worst that will happen.
Wing, rum makes everything better! Let me know how the teatree oil does! Smells better than vinegar!
 
#10 ·
The good news is, after a single night of having insulation installed and running the heater at full throttle, the boat is now DRY. The window frames have stopped sweating and my clothing is all dry. I still have two long panels to cut and install on the bulkheads in the v-berth, but that's all.

I'm mightily impressed.
 
#24 ·
That sounds like seting a heater next to an AC unit and betting on the outcome (normally one either vents or dehumidifies). Please explain.
 
#17 ·
Ah, for keeping cool in the summer, I'll put Reflectix in the windows, and stretch a white or silver tarp over a portion of the cabin top. The Reflectix is much thinner and easier to work with.

I also have a CruiseAir air-conditioning unit so...
 
#18 ·
I just use a small west marine floor heater, I have to say winter is no biggie here at 48 north, I dont do anything special and even the few weeks a year when its in the teens with ice around the boat, frozen docks and high wind I'm never cold and I'm from So cal. I let my heater run on low 24 hours a day during the coldest part of winter so the boat never gets beneath about 40 and is easy enough to heat up. I haven't done anything special as I sail year round and want to be able to leave in a moments notice.
 
#21 ·
I'm surprised so many boaters like those oil filled heaters. I hate the bloody things.
My dad bought me one, and it works OK at night(I use it at 700watts and the proper electric forced air heater at 600watts to keep the boat fairly evenly heated).
However, I find that it smells a bit, and doesn't warm the boat nearly as well as the one that moves some air, in addition the humidity stays much higher with only the oil filled one.

The worst parts of the oil filled heater is its tendency to burn things, I burn myself on it at least once a day, or melt a plastic bag onto it or something.
By contrast, the Caframo(re-branded by west marine with fewer fan speeds, the original is nicer.) helps keep my boat dry, warm and isn't prone to burning things.
 
#23 ·
I would have the oil filled heater checked. I have seen several and none of them even on high would melt a plastic bag. On 700 watts you should be able to touch it. There also should be no smell from it, at least not after a short brake in time.
 
#32 ·
Defender.com Search Results: hypervent $10/foot x 40 inches at Defender, and yes, it's worth it.

We lined the entire inside of the boat with Reflectix one winter. The esthetic was funky but it was warm!
 
#36 ·
I find this thread interesting. Usually condensation is a result of the space temperature being below the dew point. Insulation doesn't stop heat loss, it only slows it down.

My concern with installing insulation or hypervent on the outboard side of the hull is has anyone removed the product after a winter of living aboard to see what's growing behind it? When we first started building tight energy effiicent homes, we discovered that the moisture within the house eventually lead to mold problems because the houses were so tight, they did not exfiltrate. This issue was solved by the installation of heat recovery ventilators which moved that mositure to the outdoors.

In my mind a boat does not breath or exfiltrate. Ventilation really is the key to removing moisture inside a boat that creates all these problems.
 
#38 · (Edited)
I've never really been tempted to live aboard over the winter in cold weather. Looking forward to it down south one day. However, there are moments where we've thought about it.

There are two problems with moisture. First, the amount of water vapor available and the dew point, which will determine whether it remains in the air.

On a boat, it is nearly impossible to keep water from being evaporated into the air. Boiling water, showers, wet bilges, breathing, etc, etc. You will add moisture to the air, there is no stopping that.

The dew point is more complicated. It is expressed as a temperature, but is really a factor of ambient temperature and how much moisture has been evaporated into the surrounding air. The more moisture in the air, the higher the dew point will be, meaning the closer to the ambient temperature it will be. Said differently, it is the temperature at which the air would no longer be able to hold onto the amount of moisture absorbed within it. The warmer the air the more moisture it can hold. 70 degree air can hold more than 50 degree air, which can hold more than 30 degree air, which can hold more than 10 degree air, etc, etc. Reduce the temperature and there is a point where it can no longer hold the moisture within it and it condensates out.

The biggest problem with a boat in the winter, is not keeping the interior air above the dew point, its keeping the hull above the dew point. While you may keep the salon table relatively warm, put your hand on the hull inside a hanging locker or galley cabinet. It will be much colder, maybe by tens of degrees and undoubtedly below the dew point. That's why you get condensation, followed by mildew, and not necessarily where you can see it. Insulation helps, but as some have pointed out, it may only transfer the problem behind the insulation if the moist air can get behind the insulation.

The only good solution, IMO, is to substantially reduce the actual humidity in the air, thereby, reducing the dew point below even the cold hull temperature. That can only be done effectively with electric powered dehumidifiers IMHO.
 
#39 ·
>The only good solution, IMO, is to substantially reduce the actual humidity in the air, >thereby, reducing the dew point below even the cold hull temperature. That can only >be done effectively with electric powered dehumidifiers IMHO.


That works if you're tied to dock w/ shore power. The reality is you want your heating system to be capable of producing suffient air changes per hour within the boat to get rid of the moisture. It's all about pressure.

A perfect example are the diesel fired heaters like espar. You can set these up so they heat 100% outside air or recirculate the return air. Recirculating the air is more energy efficient. If you're recirculating 100% of the return air, you should consider taking in a small percentage of outside air on the return side. In doing so you pressurize the inside of your boat. By keeping a hatch cracked open you get the air changes per hour necessary to remove the moisture.

In Brent's example of using a wood stove, air is needed for combustion. Although it's under negative pressure due to the process of combsution, the air changes per hour are occuring naturally, thus removing the moisture. Plus wood produces a dry heat.

Considering the couple of examples above, it all's about ventilation.
 
#40 ·
>The only good solution, IMO, is to substantially reduce the actual humidity in the air, >thereby, reducing the dew point below even the cold hull temperature. That can only >be done effectively with electric powered dehumidifiers IMHO.

That works if you're tied to dock w/ shore power. The reality is you want your heating system to be capable of producing suffient air changes per hour within the boat to get rid of the moisture. It's all about pressure.

A perfect example are the diesel fired heaters like espar. You can set these up so they heat 100% outside air or recirculate the return air. Recirculating the air is more energy efficient. If you're recirculating 100% of the return air, you should consider taking in a small percentage of outside air on the return side. In doing so you pressurize the inside of your boat. By keeping a hatch cracked open you get the air changes per hour necessary to remove the moisture.

In Brent's example of using a wood stove, air is needed for combustion. Although it's under negative pressure due to the process of combsution, the air changes per hour are occuring naturally, thus removing the moisture. Plus wood produces a dry heat.

Considering the couple of examples above, it all's about ventilation.
The ventilation is where the hypervent comes in(or similar product) allowing those air changes to pull the moisture out from under the mattress . However, I think that insulation makes a huge difference too, as in the example of hull temperature, if the insulation keeps the surface temperature 10-15 degrees warmer(and based on my floor vs before insulating the surface, it does) that can certainly help to prevent the condensation forming in the first place.
As a secondary benefit, if it means that the air in the boat stays warmer until it is exhausted from the boat it would mean it holds more moisture.

The hyperdry in lockers at least is less about insulating, it just prevents things from touching the hull and giving that dead air space for mold to form. I've used it in my lazarette and it's making a big difference in how wet things stay(the hatch leaks badly).
 
#41 ·
This is great! I'm really getting a lot from reading thoughts on all sides of this debate and I really appreciate all of your comments! What I have done so far is: Applied mildew/mold resistant primer to the hull and put reflectix over that. The thought being that if there is any mold build up behind the insulation it will be kept to a minimum. I have ordered the hypervent for the settees and v-birth since most everyone agrees that it is a good thing. This leave me with venting or dehumidifying... Since I will need heat either way, I need to choose an appropriate heater. My boat is on 25' so it isn't much space to heat, and I do have shore power. So to redirect this thread for a sec, who is using what heaters and any opinions (and I KNOW you have them :)! ) on what may work best for my small space. THANK YOU ALL!
 
#42 ·
This is great! I'm really getting a lot from reading thoughts on all sides of this debate and I really appreciate all of your comments! What I have done so far is: Applied mildew/mold resistant primer to the hull and put reflectix over that. The thought being that if there is any mold build up behind the insulation it will be kept to a minimum. I have ordered the hypervent for the settees and v-birth since most everyone agrees that it is a good thing. This leave me with venting or dehumidifying... Since I will need heat either way, I need to choose an appropriate heater. My boat is on 25' so it isn't much space to heat, and I do have shore power. So to redirect this thread for a sec, who is using what heaters and any opinions (and I KNOW you have them :)! ) on what may work best for my small space. THANK YOU ALL!
On submarines, our greatest fear was fire or flooding. I am rather paranoid when it comes to heat producing equipment, and the load placed on electrical systems.

You really, really don't want to come back to your boat after a hard days' work and find a hull burned down to the waterline. Not to mention that you have a furry friend onboard.

First, make damn sure that your boat's shore power system is safe, and do not exceed it's load limit. (amperage)

Second, I've found that the oil-filled electric radiator heaters are much safer than forced-air fan heaters with the heater element. The oil-filled heaters have a tip-over shutoff for safety. They make a nice, dry heat.

I have a forced-air heater as a booster, but I NEVER run it unattended.
I also have a Coleman "Black Cat" catalytic propane heater, that will be my emergency booster on those few 11F degree days. I've seen 9F degrees since I've been in Maryland. It ain't pretty. The Coleman heater can be plumbed to a large propane bottle that you keep out in the cockpit if you buy the adapter kit.

pelonis-1-500-watt-portable-electric-oil-filled-radiant-heater

Forced air heater

Coleman Black Cat
 
#43 ·
Thanks for the suggestions! All of the boat's shore power system is brand new, she previously only had DC power. I agree that the electric heaters scare me too. However, it looks like you still have to plug the oil heater in. Sorry if this sounds silly, but how are the two different in that department? What makes the oil heater safer if it is still part electric? (Originally from AZ, don't need many heaters there!) I do have some of the small propane heaters also.
 
#47 ·
However, it looks like you still have to plug the oil heater in. Sorry if this sounds silly, but how are the two different in that department? What makes the oil heater safer if it is still part electric? (Originally from AZ, don't need many heaters there!) I do have some of the small propane heaters also.
The oil heater s an electric heater with the heating elements inside an oil chamber. Ther is no fan on an oil heater. They get warm and air flows by convection. The other electric heaters have a fan that blows air over exposed electric elements that glow red hot.
 
#44 ·
I wouldn't use any 'unvented' propane heaters below.. danger of CO buildup.

Our electric fan heater has a 'tilt' switch and shuts off if it falls over, I think the biggest advantage of the oil heaters is that they are quieter.

Espars and the like are thirsty both for fuel and power.. so there's no 'free lunch' as they say. If you've shore power available I think a combo of a dehumidifier and a modest heater should work. (the dehu gives off some waste heat too)
 
#45 ·
I lived aboard in Wash DC and Annapolis for three winters on an Ericson 30 (headliner with just an air space for insulation), and kept the boat comfortable with two 1500 watt forced air heaters. No condensation.
I think the key is keeping the air moving with hot air, when you heat the air it reduces the humidity. Radiant heaters don't reduce the humidity. Stay warm.
Brian
 
#48 ·
.....when you heat the air it reduces the humidity.
That's not exactly correct. The higher the temperature of the air, the more moisture is can retain as humidity. Condensation occurs when the air is saturated with moisture and can't hold any more. Heat the air and it can hold more water, but its still there.

Its super cold air that can't hold much humidity.
 
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