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I have A San Juan 23 that is on a trailer and it doesn't leak from rain much but it can be dry all week and ill go to my boat on the weekend and it will have water in the floor and water on the roof and everything will be somewhat damp and water drops on the cabin top.Any guesses?Thoughts?Solutions?:confused:
 

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Simple answer; absolutely. It can be a big problem when in colder climates. Sail to the tropics and you won't have to worry about the boat sweating.
 

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TROUBLE
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They share do and when it's humid accompanied by a large temperature change they sweat enough to put water in the bilge.
John
We live aboard, and sometimes a nice, cold drop of condensation will fall on my face from the hatch in the V-birth. That will wake you right up.

Like capta said, that never happened in the Bahamas. Not sure what I was thinking coming back to Texas for the winter.

Maybe buy yourself a de-humidifier for the boat?

Ralph
 

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it's the hull above the waterline that sweats. the air gets cold outside and the hull cools. with warm moist air inside and you get condensation
 

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For whatever reason when I had a boat on a trailer it got water inside that it never got when it was in the slip. My only explanation is that sitting on a trailer maybe the hull flexed differently than when in the water and allowed spaces for water to seep through.
 
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No, boats do not sweat. Yes, water vapor condenses on surfaces that are cooler than the dewpoint temperature. Sorry to be pedantic, but it will help you understand. I keep my boat on a trailer at Guntersville Lake and the exact same thing used to happen to me. Here's more explanation:

At night in N.Al, the air cools and the relative humidity goes up very high, especially near the lake. That means that the air temperature is close to the dewpoint temperature. Anything cooler than the air will get wet. It is possible for the deck of your boat to get cooler than the air. This is due to radiation from the boat to the black night sky. If you have ever seen dew or frost on a car left outside, but not on a car parked in a carport or under a tree just a few feet away, you've witnessed the effect of radiative cooling.

You can eliminate or at least reduce the amount of condensate in your boat by covering it with a tarp (reduces radiative cooling) and by keeping the boat open under the tarp. Keep your companionway open and crack another hatch enough to allow air flow, but not enough to allow rain in. The airflow will help keep the hull close to the air temperature and will allow daytime air, with it's lower humidity, to soak up any condensate that formed overnight.
 

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Yeah, so you've gotten a number of answers to your question. I just wanted to add that I used to own a San Juan 23. Really liked it. Excellent boat for what it is, and sails very nicely.
 

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No, boats do not sweat. Yes, water vapor condenses on surfaces that are cooler than the dewpoint temperature. Sorry to be pedantic, but it will help you understand. I keep my boat on a trailer at Guntersville Lake and the exact same thing used to happen to me. Here's more explanation:

At night in N.Al, the air cools and the relative humidity goes up very high, especially near the lake. That means that the air temperature is close to the dewpoint temperature. Anything cooler than the air will get wet. It is possible for the deck of your boat to get cooler than the air. This is due to radiation from the boat to the black night sky. If you have ever seen dew or frost on a car left outside, but not on a car parked in a carport or under a tree just a few feet away, you've witnessed the effect of radiative cooling.

You can eliminate or at least reduce the amount of condensate in your boat by covering it with a tarp (reduces radiative cooling) and by keeping the boat open under the tarp. Keep your companionway open and crack another hatch enough to allow air flow, but not enough to allow rain in. The airflow will help keep the hull close to the air temperature and will allow daytime air, with it's lower humidity, to soak up any condensate that formed overnight.
Being pendant often causes one to overlook the richness of language and the ability to convey information concisely in a meaningful manner. One definition of "sweat" is "to collect and condense water in droplets on its surface" which is exactly the process you describe.
So, I stand by my answer that boats do sweat, sometimes profusely.
John
 

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For whatever reason when I had a boat on a trailer it got water inside that it never got when it was in the slip. My only explanation is that sitting on a trailer maybe the hull flexed differently than when in the water and allowed spaces for water to seep through.
I had the same exact issue. When my boat is on a trailer, I find water in the bilge after a good rain. When it is on the water, its completely dry. I though it might be the angle in which it sits on the trailer but I think Donn'a explanation is more likely.

The weather we've had lately definitely leads to condensation. I've found that a small fan keeping the air moving helps a lot.

-Chris
 

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Ever walked across a grass lawn right after sunrise? And found it soaked with condensation and dew so your feet are now soaking wet?

Well, that's what happens on fibergrass boats, too. Moving to Arizona can cure that.
 

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I'll add that boats don't always sit at the same angle on their trailer as they do in the water... this can easily create places for water to pool, or enter, beyond condensation, that would otherwise ALSO happen.

My Capri 25 was dry as a bone in the water... and took on water on the trailer in the rain. Turns out the nose was up just enough so water didn't run directly off the coach roof, but instead ran along the hatch tracks, and dripped down below. I'd routinely have water on the floor below, ABOVE the bilge... Bilge would stay dry. Prior owner rarely had the boat in the water, told me it had a leak and he couldn't figure it out. I bought it from him and put it right in the water, and never noticed it, until I hauled for the winter. Then I went on a mission to figure out where it was coming from. A couple minutes down below, while on the trailer during a rain storm, and viola!
 

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Being pendant often causes one to overlook the richness of language and the ability to convey information concisely in a meaningful manner. One definition of "sweat" is "to collect and condense water in droplets on its surface" which is exactly the process you describe.
So, I stand by my answer that boats do sweat, sometimes profusely.
John
OK, but saying "boats sweat" often causes one to overlook that condensation is happening on all surfaces that are cooler than dewpoint, even if they do not "sweat." Have you ever seen a cotton shirt sweat? No. But you probably have seen cotton fabric full of mildew. That's because condensate forms on cotton just like it forms on boat hulls. The cotton, however, absorbs the moisture before in coalesces into droplets.

Now, by understanding that boats don't sweat but water vapor condenses, we've explained how trailered boats get wet without rain, and how things in boats gets mildewy. The solution to both problems is to prevent the surfaces from getting cooler than the dewpoint. One can raise the surface temperatures or lower the dewpoint of the air. A dehumidifier does both, but expensively. Leaving the cabin open to air convection solves the problem cheaply.
 

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What you're seeing is pretty common. The same thing happened with our Catalina 22 when she was on her trailer.

You might try adding a solar fan to keep the air moving.

Defender, Solar Fans
 

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Being pendant often causes one to overlook the richness of language and the ability to convey information concisely in a meaningful manner.
He was being a hanging ornament? Hmm. I didn't notice that at all. :D

I believe the word you meant to use was "pedant." I always find it amusing when someone gets snippy with others for their language errors, and in the process makes language errors themselves.
 

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Sorry, I sometimes miss ipad autocorrections, which may have happened in that post. I had the ditionary in front of me in an attempt to be accurate. Alas, we all make errors.
Thanks for your autocorrection.
John
 
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