suggestions condensation problem?

[steelguy]

Having just finished covering my berth hull walls with white oak paneling, I have become acutely aware of a condensation problem in my fiberglass Sisu. The condensation literally drips off the 1/4" thick 10" high vertical transition from the thicker 1-1/4" bow deck and adjoining gunwales. My boat is up in Alaska and when the interior space is warmer than the exterior, the oak, yet to be sealed and finished, gets pretty wet. My plan at the moment is to cover the interior ceiling surfaces, including the thinner 1/4" step sections, with synthetic carpet tiles. I'm hoping that the carpet will create a thermal break and stop the condensation. That being said, I am altogether open to any suggestions.

 

[ksanders]

I am in Alaska and have seen and experienced what you are talking about.

Ventilate your boat and the problem will go away.

 

[steelguy]

why didn't I think of that?! Do you think a passive vent will work, or something with a fan? If you're able to suggest a specific vent, I'll look into it. Thanks!

 

[tpbrady]

I agree with Kevin to a point. When the fiberglass is both an interior and exterior wall and you are sleeping in the area, its difficult to get enough ventilation to prevent all moisture. In our forward V-berth and aft master stateroom, we get condensation on the area where the interior walls are uninsulated and attached directly to the outside fiberglass no matter how many windows are open. I have solved the issue in the main cabin for the most part using insulation on top of the paneling. I am still debating what to do long term. In the v-berth, I intend to coat the interior fiberglass with a product called Mascoat. I used it in a C-Dory and it cut condensation inside by better than 90% after 3 nights in the rain with the windows cracked and the cabin door open. The same situation without the Mascoat saw everything inside damp with visible water on all the fiberglass services. To dry the inside, I ran the heater almost constantly. As an insulating layer it did exactly what the manufacturer said it would.

Tom

 

[ksanders]

why didn't I think of that?! Do you think a passive vent will work, or something with a fan? If you're able to suggest a specific vent, I'll look into it. Thanks!

We used the Vetus power vents with great success. They draw almost no power and work much better than the solar units with battery backup here in Alaska.

 

[ksanders]

I agree with Kevin to a point. When the fiberglass is both an interior and exterior wall and you are sleeping in the area, its difficult to get enough ventilation to prevent all moisture. In our forward V-berth and aft master stateroom, we get condensation on the area where the interior walls are uninsulated and attached directly to the outside fiberglass no matter how many windows are open. I have solved the issue in the main cabin for the most part using insulation on top of the paneling. I am still debating what to do long term. In the v-berth, I intend to coat the interior fiberglass with a product called Mascoat. I used it in a C-Dory and it cut condensation inside by better than 90% after 3 nights in the rain with the windows cracked and the cabin door open. The same situation without the Mascoat saw everything inside damp with visible water on all the fiberglass services. To dry the inside, I ran the heater almost constantly. As an insulating layer it did exactly what the manufacturer said it would.

Tom

Hi Tom, I'm trying to remember if we've met in person? (getting old, sorry).

I will add that even with ventilating I sometimes got "wet bunk" where the bunk laying on a cold surface seemed to collect moisture.

I solved that issue with pink hard foam insulation from Home Depot. I put that under the mattresses and never a wet bunk again.

I will also agree with you that the transition times, where it is too warm to run the heater, yet cold and rainy outside are the hardest to deal with.

We have four large dogs, plus people, and sometimes I've ran the heat on low with the door open just to keep things from getting moist inside.

 

[obthomas]

The problem is basic. Wet air meets with cold surface. To prevent condensation you have basically two choices.

1. prevent or control wet air from entering the boat
2. eliminate the cold surface.

Drying the air entering the boat is the most difficult.
Insulating the cold surface is the easiest.

What I have done to solve the problem is a combination.

I run a dehumidifier constantly and have glued foam insulation to much of the hull inside my boat.

Good luck guys.

 

[Boydski]

I will also agree with you that the transition times, where it is too warm to run the heater, yet cold and rainy outside are the hardest to deal with.

Hi Kevin,

Have you ever tried running a dehumidifier inside the boat (when you have shore power)? I run a larger, low-temperature unit on a timer during our wet months (we have a LOT of wet months) and it keeps the humidity down to 50% on the boat. Most of the low temp versions will work down to 40° or so before they freeze up.

An hour+ each morning seems to dry up the boat, even after showers and sleeping.

 

[bayview]

People breathing and sweating and cooking add a lot of water to the air. I wonder if some method of exhausting hot humid air while adding dry heat might help.

I always suspected that insulation just hid the problem unless something stopped the damp air from touching the cold surface.

I use a dehumidifier in FL to reduce humidity without running the HVAC all the time. It does seem to work but the range of operating temps seems limited. But I guess if you are living aboard the temps are OK.

 

[obthomas]

I always suspected that insulation just hid the problem unless something stopped the damp air from touching the cold surface.

You are right...It is very important that the insulation be next to the hull otherwise condensation develops behind the insulation. This is why I glue the insulation in place.

 

[Moonstruck]

Ventilation
insulation
dehumidification

 

[bayview]

Quote:
Originally Posted by bayview

I always suspected that insulation just hid the problem unless something stopped the damp air from touching the cold surface.

You are right...It is very important that the insulation be next to the hull otherwise condensation develops behind the insulation. This is why I glue the insulation in place.


Then I guess the insulation has to be water vapor proof like Styrofoam, not carpet or that pink batten stuff used in homes.

 

[Moonstruck]

Quote:
Originally Posted by bayview

I always suspected that insulation just hid the problem unless something stopped the damp air from touching the cold surface.

You are right...It is very important that the insulation be next to the hull otherwise condensation develops behind the insulation. This is why I glue the insulation in place.


Then I guess the insulation has to be water vapor proof like Styrofoam, not carpet or that pink batten stuff used in homes.

If you are putting something like spun fiberglass insulation against the hull with no ventilation between, You should seal the inside with something less than one perm. Like 4 mil. poly. The condensation migrates to the outside.

 

[FF]

With or with out insulation the water will condense when it gets cold enough.

If the center of your insulation is the spot , thats where the water will form.

Big hassle in a wooden boat , only a minor hassle in a plastic boat.

Use ceiling to keep the water away from view and set up simple gravity drains to lead the water down to where it can be pumped.
Just try to drain it into the bilge NOT over the AC or noisemaker.

 

[ksanders]

Hi Kevin,

Have you ever tried running a dehumidifier inside the boat (when you have shore power)? I run a larger, low-temperature unit on a timer during our wet months (we have a LOT of wet months) and it keeps the humidity down to 50% on the boat. Most of the low temp versions will work down to 40° or so before they freeze up.

An hour+ each morning seems to dry up the boat, even after showers and sleeping.

I've thought about it, but using the furnace both with and without heat on works pretty good.

I might get a small one for the lower cabin areas. No real problems but for example a towel never seems to dry.

 

[Boydski]

I might get a small one for the lower cabin areas. No real problems but for example a towel never seems to dry.

I have my dehumidifier positioned so it blows dry air across the towel hooks, so they dry really fast!

The air intake for one of my heaters also picks up dehumidified air and blows it into the Master Head to dry it out. Keeps the mirrors from getting steamed up.

 

[psneeld]

I've thought about it, but using the furnace both with and without heat on works pretty good.

I might get a small one for the lower cabin areas. No real problems but for example a towel never seems to dry.

Yep...towels can be a pain...in the winter we had one of those oil filled radiator heaters next to the bed in the master stateroom.

After the first spring the SO made me bring it back all year as she loves it on low as a towel dryer/warmer. I gave up thinking it was ever leaving so I just hard wired it into an outlet.

 

[gwkiwi]

We run a full size dehumidifier in the engine room when condition are humid, it's amazing that overnight we can fill the 2 gallon container up.

Luckily we don't get dripping like many others do but again the dehumidifier is awesome...

 

[Rustybarge]

Having just finished covering my berth hull walls with white oak paneling, I have become acutely aware of a condensation problem in my fiberglass Sisu. The condensation literally drips off the 1/4" thick 10" high vertical transition from the thicker 1-1/4" bow deck and adjoining gunwales. My boat is up in Alaska and when the interior space is warmer than the exterior, the oak, yet to be sealed and finished, gets pretty wet. My plan at the moment is to cover the interior ceiling surfaces, including the thinner 1/4" step sections, with synthetic carpet tiles. I'm hoping that the carpet will create a thermal break and stop the condensation. That being said, I am altogether open to any suggestions.

I've got tin foil covered bubble wrap as insulation on my steel boat; very disappointing result. There's still lots of condensation forming behind the bubble wrap as it's very hard to get it to stick properly to the steel surface; even the tiniest air pocket will allow condensation to form.

The old trick of the trade was best: foam backed carpet stuck onto the surface.
I've been in a steel ocean cruising sail boat with this arrangement: not a drop of condensation, and the pile of the carpet keeps the humid air away from the cold surface...

Plus : it's cheaper than chips to buy.

 

[steelguy]

agree on carpet

thanks for all of the responses and suggestions, seems this condensation problem is not limited to thin wall fiberglass walls. The bow deck and the gunwales are thicker with fiberglass sandwich balsa core, which I'm guessing is the reason they do not sweat. With the commercial synthetic carpet tiles, which are mildew resistant that I have been looking into, the 24"x24" squares come with a 1/4" thick black foam backing. I'm guessing that backing, along with the carpet pile will provide the thermal break needed to do the trick. This passive approach, versus dehumidifying and heating, seems worth trying. Plus, it has the advantage of offering a visually acceptable finished surface.

 

[Rustybarge]

thanks for all of the responses and suggestions, seems this condensation problem is not limited to thin wall fiberglass walls. The bow deck and the gunwales are thicker with fiberglass sandwich balsa core, which I'm guessing is the reason they do not sweat. With the commercial synthetic carpet tiles, which are mildew resistant that I have been looking into, the 24"x24" squares come with a 1/4" thick black foam backing. I'm guessing that backing, along with the carpet pile will provide the thermal break needed to do the trick. This passive approach, versus dehumidifying and heating, seems worth trying. Plus, it has the advantage of offering a visually acceptable finished surface.

Forgot to mention that I have an alloy roof on my Cat which is open at the sides, and yet condensation still forms on the inside surface of the roof in the winter...

...ventilation will not stop a difference in temperature between the morning mist on top of the water, and the inside of the metal roof.

 

[kelbylinn]

We use two of these small air driers from west marine. Works for us here on the gulf coast.