moisture problem inside your boat and want to fix it?

[centerline]

some boats have dry interiors without the use of air conditioners/dehumidifiers and many others not so much. its not the brand of boat that is responsible for this, but its how someone has created ventilation to allow the moisture to escape.

if you have spent the money to buy a true dehumidifier or air conditioner, then you have bypassed any need for ventilation to allow the moisture to escape.
for the people that dont want to, or cant afford to spend that much money, ventilation is the absolute cheapest option to help dry the boat.

insuring there are no leaks to allow water in is the first thing that needs to be done, no matter if you use a dehumidifier/air conditioner, or just ventilation alone, the hull/caulking needs to prevent any water seepage into the interior of the boat to maintain a dry enviroment.

I was reading here and elsewhere, that some people seem to think there may be something wrong with their boat because its always damp inside, or that there is some magical formula to making it dry inside.
excess dampness inside is not an uncommon problem, but it should be because the fix is pretty easy compared to some of the other things we do to our boats.

and its not a secret... ANY boat can be dry if it has enough ventilation to allow the moisture to get out.
but even though the outside air will always be drier than the air inside the boat, in the natural environment, no amount of ventilation will ever be able to dry the space any drier than what the outside air is....

anyone who has the problem, and yet does not fully understand the problem, is going to be forever aggravated by it... and so are those that do understand the problem but do nothing about it.... talking, worrying, wondering and complaining about it wont ever dry the boat out.
basically, their are only 2 reasons for a "wet" boat....
#1 is... the owner knows of and understands the problems (or not) but doesnt care. he/she feels the time/cost to repair it is not worth the investment.
#2 is.. the owner doesnt understand the reasons that the boat is always damp inside (yet would fix it if they knew what to do about it)

and there is a third reason which shouldnt even qualify, but it is the single biggest reason most boats have a moisture problem...
the owner has undoubtedly heard over and over many times that ventilation will help eliminate their problem. but they reject it as an option because it takes some effort on their part, and it may even be hard for them to believe something as simple and cheap as ventilation could cure such a destructive problem. so they buy a small device from a salesman that claims to "dehumidify", without understanding the basics of how a true dehumidifier actually works.

EDIT... see the links to the cheap "dehumidifiers" that I am referring to... a real dehumidifier, one that actually removes the moisture from the air and space is much different than what is shown in the links.
the ones shown here are being sold way too often to solve a damp problem in a boat, because they wont do it. these are just a few of what you may find available that is being sold as dehumidifiers
if you have a proper dehumidifier then you have paid dearly for it and dont have a Dampness problem... but just because it says on the package that it is a dehumidifier, doesnt mean it actually is..

link 1

link 2

link 3

link 4


as for damp boats and spaces, here are some absolute truths that may help some to understand the issue.
then you can go forth with very little cost, time or effort, relatively speaking, and fix the problem forever.

#1... even on a wet rainy day, when the heater is going in the closed up space of the boat, the air outside will always be drier than the air inside the boat. you NEED ventilation so the air can exchange.

#2... people install a cheap $50 "dehumidifier" or heater to dry the space out, but these items only help to evaporate the moisture into the air.

#3... there is only so much moisture the air can hold at any given temperture, and if there is no ventilation so that warm wet air can not get out, it will contact the cooler surfaces of the boat and condensate into moisture... and the cycle begins again.

#4... people assume that heat is the answer to a dry boat. but it is NOT.... all you need is ventilation... and if there is air movement in the dampest areas, such as a small fan, it will multiply the effects of the ventilation....

#5... a fan, or other means of forced air movement is better for evaporating moisture from the boat surfaces than heat is. ALWAYS.

#6... warm air will hold a lot more moisture than cold air, so applying heat to the area will allow the air to carry more moisture out quicker, when there is adequate ventilation.

#7... because of fact #6, it is much easier and cheaper to have a dry boat in a cool northern environment than it is in the tropics.

#8... heat applied to a damp area without ventilation will cause mildew many times quicker than no heat at all in the same area.

#9... good ventilation in a damp area, with some air movement is very unlikely to grow mildew.... EXCEPT for the areas of the space that doesnt get the air movement, such as under a pillow or between the folds of a sail, ect.... any air movement especially without heat becomes a very harsh environment for the mold and mildew, and so it doesnt readily grow there.

#10... contrary to what the salesman of the small $50-$100 electric dehumidifiers want you to think, they DO NOT dehumidify. by definition, dehumidify would mean "removing the moisture"... all these units do is suspend the moisture in the air. its up to YOU to make sure the air gets removed from the space so drier outside air can take its place and absorb more moisture. this is called ventilation.

#11... any boat that continually has an influx of moisture from a hull crack, leaky deck fitting/rail, faulty fresh water fitting, hose or tank, ect. has a problem that will multiply the effort needed to dry it out.
the term multiply here does not mean twice as much effort, but it means many more times the effort.

#12... as inferred by #11, you must keep the bilge dry or you will need an excessive amount of ventilation while attempting to dry the boat out.

some of these points may seem a bit redundant, but so is repeating over and over and over in many threads by many people on many forums and sites, that you need some form of active ventilation (cheap)... OR a mechanical device (costly) that seperates the moisture from the air, and discards the water outside of the space.

hot climates only intensify the problem and the desire to fix it.
so if the boat happens to be located in a humid atmosphere, such as the SE coast, gulf coast, ect. where the air is hot and humid, these absolute facts still hold true, but because hot air can hold an excessive amount of moisture, even with excellent ventilation throughout the boat the air can still hold more moisture in it than we want to put up with, so a true dehumidifier will be needed to condition the air to the levels we are comfortable with.

there is no magical device that has ever been created in this world that can dry out an enclosed space unless it has a way to move the moisture to the outside of it.

ventilation is natures best way of doing this for us... but as man is always wanting more and better, along came Willis Carrier and invented/designed a mechanical device called the dehumidifier and hence the air conditioner, of which both work very well, but are much more complicated and expensive than the small cheap devices shown in the links above

 

[kappykaplan]

Well stated, centerline.

 

[thinwater]

Nice rant, and mostly correct.

1. Depends. If there is snow on the deck (common in many parts of the country) or the harbor water is significantly colder than the air (common in the NE in the spring) the inside surfaces of the boat can be significantly below the dew point. There will be condensation, though good ventilation can reduce the duration by drying the boat when conditions change.
4a. If heat is required for occupation (it is in the winter) then things are a whole lot more complex. There will be more water in the air, there will be cold surfaces, and multiple solutions will be needed. Properly installed (vapor barriers etc) insulation is generally required.
9. There are true dehumidifiers that remove water. Obviously, these will have a drain. A true dehumidifier can maintain the RH ~ 50-60%, outperforming simple ventilation.

 

[Chris Patterson]

Suspend? Some more research is needed here. MY dehumidifier captures moisture, and drains it back to a tank or drain hose. If Jesus told me all I was doing was suspending moisture, ( which is what a HEATER does), I'd call him out.

 

[Benny17441]

I appreciate the effort for the list and it might be very practical at your geographic location but allow me to say that it may not work as well for some of us here in the Gulf of Mexico. In the summer time we suffer from high ambient humidity values in the 90%+. We get mildew on our topsides. To rely solely on passive ventilation will not prevent mildew inside the cabin. After much experimentation I have found that it is best to lower the humidity inside the cabin and keep the boat locked up to keep the more humid air outside. Obviously I'm talking about when the boat is unattended as it is impractical to pursue when the boat is being used. We use a compressor driven electric dehumidifier powered by shore power. It has a thermostat that allows us to set the desired degree of humidity. The unit removes water out of the air by condensing it into canister and it gets routed by a hose into the bilge where it is expelled outside. The cabin air is also used to cool the compressor and the resulting effect when you open up the boat is dry heat. Anyone familiar with the weather in Arizona in the summer months will be familiar with the concept of dry heat. The air is hot but there is not enough humidity in the air for comfort. We actually have to limit the desirable humidity inside the cabin to no lessthan 55% as to protect the rubber in the cushions. I understand that you fellows in colder and dryer areas, forget about the rest of us that have to deal with some differing conditions, when providing advise.

 

[Chris Patterson]

That is absolutely correct, Sir.

 

[woodster]

i went to a football game in Phoenix AZ in Sept one time to watch the falcons and cardinals play ...it was 107 that day and it felt like i was standing next to a pizza oven ...i drank 4 liters of water at the game and not one drop of sweat was on me the hole time...i learned that if you go out west you better drink lots of water .....not here in hot-Atlanta in the summer time i can read the word water and will be soaking wet with sweat and if you use a dehumidifier here you better have a good one or it will work its self to death trying to keep up....

 

[Head Sail]

#2... people install a dehumidifier or heater to dry the space out, but these items only help to evaporate the moisture into the air.


#9... contrary to what the salesman of the small electric dehumidifiers want you to think, they DO NOT dehumidify. by definition, dehumidify would mean "removing the moisture"... all these units do is suspend the moisture in the air. its up to YOU to make sure the air gets removed from the space so drier outside air can take its place and absorb more moisture. this is called ventilation.

I'll have to respectfully disagree with these statements.
Humidifiers don't evaporate moisture into the air:naughty:, they condense moisture into liquid form (water) which is collected in a pan or drained overboard through the galley sink, thus reducing the amount of moisture in the air.

 

[centerline]

Suspend? Some more research is needed here. MY dehumidifier captures moisture, and drains it back to a tank or drain hose. If Jesus told me all I was doing was suspending moisture, ( which is what a HEATER does), I'd call him out.

As stated, a cheap "dehumidifier" will not dry the boat out unless there is a way to REMOVE the moisture to the outside of the boat... if yours has this capability, then it isnt the cheap $50-100 units that is so commomly sold to boatowners to dehumidify their boat.

I was in the local boating store saturday and seen the salesman promising a customer that "we sell lots of these to people to dehumidify their boats".... but it was not a dehumidifier... more like a small engine room heater..

 

[centerline]

I'll have to respectfully disagree with these statements.
Humidifiers don't evaporate moisture into the air:naughty:, they condense moisture into liquid form (water) which is collected in a pan or drained overboard through the galley sink, thus reducing the amount of moisture in the air.

You are right that a true dehumidifer does work and i am wrong for not being more clear on this... i cant edit from my phone here, but i can later.

And yes, it is kind of a rant, but with lots of truth. There are a few devices sold as dehumidifiers to the poor folks looking for a way to dry their boat out, and it doesnt work for them.... obviously for those that spend a few more dollars on the right equipment, it will take the moisture from the inside to the outside..

Ventilation will also do this for those that either cant afford the more expensive unit, or for those that cant afford the power consumption, such as when away from the dock.

 

[Head Sail]

You are right that a true dehumidifer does work and i am wrong for not being more clear on this... i cant edit from my phone here, but i can later.

And yes, it is kind of a rant, but with lots of truth. There are a few devices sold as dehumidifiers to the poor folks looking for a way to dry their boat out, and it doesnt work for them.... obviously for those that spend a few more dollars on the right equipment, it will take the moisture from the inside to the outside..

Ventilation will also do this for those that either cant afford the more expensive unit, or for those that cant afford the power consumption, such as when away from the dock.

I don't know why the call those little round heaters dehumidifiers.:Liar: That's like calling a light bulb a dehumidifier. I suppose they warm the air slightly thus lowering the relative humidity level but your correct in that they don't remove moisture.

 

[Maine Sail]

#10... a boat that continually has an influx of liquid from a hull crack, leaky deck fitting/rail, faulty fresh water fitting, hose or tank, ect. has a problem that will multiply the effort needed to dry it out.
the term multiply here does not mean twice as much effort, but it means many more times the effort.

This is the primo, numero uno reason why boats are damp. DRY YOUR BILGE....

Wet bilge, your boat will never be as dry as you want... Pour just a little water into a glass bottle, now close it up. How long the the moisture in the bottle remain at high levels? Until you drain all the water out... Drain the water put the stopper back in and the bottle will be dry.. Your boat is a bottle. Ventilation is great, we have tons on our boat, but it can only do so much if you are doing your damnedest to create an internal eco-system by having a pond in your house.....

I work on hundreds of boats, many with a lot more ventilation than ours has. Our boat is the driest boat I know or set foot on. Why? We have a dusty dry bilge. Ever been to a house with an indoor pool......

BTW true dehumidifiers do work, if you drain it to the exterior of the boat...

 

[thinwater]

Yes, it is a shame that unscrupulous marine vendors call a small heater a "dehumidifier." This is conflict with standard English definition and usage and thus is simply commercial fraud.

Read that, Davis et. al.

 

[woodster]

Yes, it is a shame that unscrupulous marine vendors call a small heater a "dehumidifier." This is conflict with standard English definition and usage and thus is simply commercial fraud.

Read that, Davis et. al.

a box of saltine crackers would make a better dehumidifier than that crap they call a dehumidifier

 

[jamarohn]

drier outside air can take its place and absorb more moisture. this is called ventilation.

I wish our outside air was drier. Currently it's at 85% humidity. And that is normal in my area (PNW) for this time of the year. Ventilation means drawing in this wet moist air into my cabin. I do not want moss growth in my cabin (natures way of capitalizing on our rain forest ecosystem).

 

[centerline]

This is the primo, numero uno reason why boats are damp. DRY YOUR BILGE....
Wet bilge, your boat will never be as dry as you want...

BTW true dehumidifiers do work, if you drain it to the exterior of the boat...

I know this to be true.... we bought our boat during the winter months and it had a minor water influx problem.
I repaired the drip but didnt dry the bilge any more than the pump would suck it out.... so for a few months we had dampness in some of the compartments.... when I cleaned the bilge and mopped up the debris and water, the boat became dry, without changing the amount of ventilation.

but, before drying the bilge, I could leave the hatch and a portlight open, and the compartments would dry out.... so ventilation is good, but a dry bilge is better.

and yes, a PROPER dehumidifier does work.... I edited my original post.

 

[Hello Below]

#4... people assume that heat is the answer to a dry boat. but it is NOT.... all you need is ventilation

Maybe.

Pacific North West. My boat, as most do here, stays in the water year round. I do some winter sailing thus I do not winterize the engine nor the fresh water system nor the head as I need them to well . . . winter sail. When not sailing I sometimes work on the boat and thus need some warmth in the boat to keep the blood moving in hands and brain. The temperature outside at this minute (8 PM) has drop to 36F and the humidity is 87%. In order to keep the systems from freezing, if the temp drops like it is right now, I use heaters. I keep the boat between 50 - 60F. This may cause condensation so I circulate internally and dehumidify, but no (or little) interior/exterior air exchange. My bilge is bone dry.

In my case I cannot just VENTILATE nor can I just DEHUMIDIFY as I would be hard press to find a dehumidifier that effectively operates at below 60F or 50F or 40F.

I think each of us must consider our own situation including what area that we live in and what conditions we want inside the boat at any given time. In the PNW, if you put the boat to bed in Nov and open it back up in Apr, then winterizing and ventilation is all that is needed. If you sail at all or work onboard doing projects then you need heat, dehumidifying and circulation.

There is no one rule that applies across this huge continent.

Len

 

[centerline]

There is no one rule that applies across this huge continent.

Len

you are right, there is no one rule that applies across this huge continent, thats why I listed several of them.... there are plenty more also.

in the context of my original post, which a LOT of people are straying from and off on their own tangent, was meant to explain that "any boat that is outside and floating in the water and has the cabin closed with little to no ventilation for any length of time, in ANY temperture/climate, will have a damper interior, than will the boat setting next to it in the same conditions that DOES have good ventilation".

adding heat to both boats to keep things equal, the results will be the same, but the enclosed boat will be warmer and quite possibly even damper than the boat with good ventilation, due to the air actually being able to suspend more moisture, allowing more surface area free for additional moisture to condensate on.
the heat in the ventilated boat will suspend the moisture, and the ventilation will allow it to escape letting in drier, cooler air.

so in a 3+ month period it will be no different except that the boat without ventilation will likely be growing mildew, where the boat with good ventilation will have a very low probability of having any...

warmer climates only intensify the problem, and people living or otherwise occupying the interior space of the boat can also intensify the problem, but at the same time may allow better ventilation... but the amount of ventilation may not always offset the amount of moisture being created by our bodies, cooking, washing, ect.... but with enough ventilation the interior can be as dry as the exterior without mechanical means of removing the moisture.

here are a couple more rules that apply across the continent, concerning moisture that causes condensation in our boats....

northern climates have less moisture in the air than a southern climate does.... but the outside air will still be drier than the inside air...

air with cold snow falling thru it in the dark of winter is drier than the air of a warm sunny spring day...

a hot summer day on the bay, ocean or at the marina is more humid than the same area when its cold and raining....


I would respectfully like to say that I know what you meant in your post, but like all things we write, no matter if it is you, or if it is me, or if it is someone else, anything can be taken out of context and argued..... it happens on this site (and others as well) all the time, but at least here its not in any kind of malicious way, which is good....

heat alone will not cure or help with the DE-humidification process, but ventilation will always help and can actually cure it.... and when you pair the two of them together, its a winning combination as you already know.

if water creeps in thru a fitting or hull crack faster than it can be evaporated and removed with the heater and the ventilation, then it will never dry out. but then buying an expensive dehumidifier wont cure the problem either....

the context of my original post is explaining to people who have a wet boat and cant understand why, that THEY MAY NOT NEED TO SPEND THOUSANDS ON A DEHUMIDIFIER OR AIR CONDITIONER TO FIX THE PROBLEM... the solution could be right at their fingertips.

and anyone who argues that ventilation wont help cure the problem, if not entirely fix the problem, has their head in a vary tight dark hole... somewhat like an ostrich with his head in the sand, only different

and I have edited my original post to be a bit more wordy and to clarify some of the content so it is a bit harder to be taken out of context.... but im sure it will still happen

 

[Ken Cross]

Centerline
I have to say thanks for bringing this up I agree with your posts. We've been looking at used boats and I've been amazed at how wet some of them have been. One boat we looked at had the floor boards floating. I didn't look at that one for long. Usually my nose tells me when a boat isn't dry.

Interestingly enough, I am in the process of buying one that isn't dry. The problem is we really liked the boat. I now will need to rebed the outside hardware. I'm pretty sure I know where the problems are however. After that, I'll work on ventilation.
Ken

 

[fox islander]

...I'm also in the PNW. I run a small west marine heater on lowest setting...600w I believe from November until end of march and have two fans pushing air around inside the boat. No mechanical ventilation. I also chase down leaks tenaciously. The boat is dry.