Fighting condensation on cold surfaces

[Mr Fox]

Hi all

The underside of the toe rails, which run above the shelves along the sides of the cabin, get condensation on cold nights (as obviously they are cold from the outside air, causing water vapor inside the cabin to condense on them). The ceiling itself does not seem to have this issue. I'm not sure if it is a thicker fiberglass or if it just gets better circulation from the cabin fans. The entire underside of the cabin top is unfinished fiberglass with paint on it (so its a little rough in texture).

I was thinking of attaching something to the undersides to insulate them better, but I don't want to stick a foam backed vinyl on them (I hesitate to use spray adhesive to attach the foam in case it needs to come off again). I was wondering if I could use 1.5mm oakum plywood with something thin behind it, or if there are any other options you all know of that would be in keeping with a traditional looking interior. Also if there is another way to mount a liner (perhaps with screws into thin wood strips adhered to the fiberglass).

Any ideas?

Thanks

 

[Will Gilmore]

Have you considered a high-build epoxy paint? The thicker coating may be all you need to get that extra insulation. I know some basement wall treatments work from just adding that little extra layer to slow down the temperature-energy transfer.

Just a thought.

-Will (Dragonfly)

 

[Mr Fox]

Thanks I will give that a look, will it dry smooth? I might like to paint some other spots if so for a nicer appearance in the cabin.

 

[SG]

On you Marshall 22, are you getting condensation on the bolts that penetrate the deck? If you take a picture it would help.
You have accessible conditions and inaccessible conditions, don't you? If the issue is the underside of the deck, then you'd have different solutions to consider.

I'm skeptical of the use of a paint alone. Epoxy paint isn't much of an insulator, in my experience.

Unless you keep the moist air away from the cold surfaces where condensation occures, "hiding it" will only develop mold and mildew where you can't get to it. That's why there are vapor barriers on the warm side of the insulation; and the "cavities" in exterior walls and roofs are ventilated.

Take a few pictures of the various conditions. Then I think we could look at what the issues are. HOW LONG are you going to be trying to sail up there in Falmouth?

 

[shemandr]

My idea prolly doesn't fit the traditional look spoken about but pieces of styrofoam screwed onto the studs might work. Maybe they could be shaped into creative shapes. They can be replaced as soon as they become befouled with mold. Very cheap if you keep an eye on delivery packing.

 

[Mr Fox]

It’s not around any bolts (there are none through the toe rail, only the cabin top). Its a completely flat horizontal surface about 16” wide and 6 feet long, where the cabin top meets the hull, basically the underside of where you walk when going to the bow on deck. Its completely accessible, when lying in a bunk you are staring up at the area in question (does that help visualize it?).

The entire flat surface gets moist like a cold aluminum can on a summer day, it doesn’t get enough moisture to drip.l but it bugs me. Its probably concentrated there because someone is sleeping under it (breathing and being a moist human).

Maybe best to just keep a cabin fan blowing at the bunk all night? I was thinking a thin wood panel might transfer less cold from the outside- but maybe it would just condense on the surface of the wood?

Edit- not my boat but they are all the same basically inside- you see the curved cabin ceiling meets the vertical surface where the potholes are, under that is a horizontal surface that extends from under the “wall” with the portholes to the top edge of the hull (there’s no seam there all Marshall’s cabin tops are bonded to the hull). That’s the spot.

 

[DArcy]

How much thickness can you accommodate? A thin veneer of plywood (maybe 1/8") over a 1/2" or 3/4" blue Styrofoam would probably go a long way. You could even box it in so you don't see the edge of the foam.

 

[Mr Fox]

I think that could work- I saw some okume marine grade ply at 1.5 mm, so that over a 1/2” of foam would be pretty thin. Think bonding some 1/2” battens to the fiberglass which the ply could attach to (with the foam in the space between battens) would be the way to go? Would look nicer than the unfinished glass anyhow...

Gotta head to the boat and measure.

 

[Will Gilmore]

I like the wood idea. You probably don't need much more insulation. Maybe use a foaming glue like Gorilla glue. Encase the wood in epoxy first. It will look nice. If it doesn't work, peel it off and you're basically back where you started. The foam in between would certainly work. Go with even less thickness. 1/4" styrofoam and case it in with the 1/8" plywood.

will it dry smooth? I

The high-build epoxy paint will smooth it out. Use multiple coats. I can't really say how much insulation an epoxy-based barrier coat will give, but I know there are products on the market that are designed to provide an anti-condensation barrier
Thermilate InsOpaint Anti-Condensation Paint

Good luck

-Will (Dragonfly)

 

[jssailem]

I have sides of my hull in the V-Berth exposed to the interior. It is cold on the outside and warmer on the inside. I placed Reflectix Insulation (aluminum foil bubble wrap) on the exposed hull. Along with ducting in outside air and a diesel forced air heater, I was able to eliminate the condensation in the V-Berth. No mold growing behind the insulation. It is not perfect yet it is enough in my case to stop the internal moist air (my hot breath) from forming on the cold wall surface. It would be worth a try to see if it will work for you.

The heating distributor told me the trick was to get the “drier” outside air into the boat to deal with the condensation issue.

If that does not resolve the issue, perhaps you could get some computer fans (small, low volume, quiet) to move the Air in the area of your concern. This would not have air “blowing” on the bed. It could be just enough air movement to address the problem.

 

[All U Get]

You can get plywood with the grain all running in one direction so it can be bent in a tight radius. On my headliners the thin plywood has two strips of velcro glued to the back with similar strips glued on the cabin top. I need only to press it in place then affix the molding pieces around the edge. The face of the plywood has a cabin liner glued to it, similar to a car liner, which provides a nice finish.

 

[Mr Fox]

The high-build epoxy paint will smooth it out. Use multiple coats. I can't really say how much insulation an epoxy-based barrier coat will give, but I know there are products on the market that are designed to provide an anti-condensation barrier
Thermilate InsOpaint Anti-Condensation Paint

That stuff looks interesting- thanks for the info.

 

[Project_Mayhem]

I've heard of many sailors and RV's using foil backed bubble wrap with success. I haven't tried it myself so I can't comment beyond that

 

[TomY]

It’s not around any bolts (there are none through the toe rail, only the cabin top). Its a completely flat horizontal surface about 16” wide and 6 feet long, where the cabin top meets the hull, basically the underside of where you walk when going to the bow on deck. Its completely accessible, when lying in a bunk you are staring up at the area in question (does that help visualize it?).

The entire flat surface gets moist like a cold aluminum can on a summer day, it doesn’t get enough moisture to drip.l but it bugs me. Its probably concentrated there because someone is sleeping under it (breathing and being a moist human).

Maybe best to just keep a cabin fan blowing at the bunk all night? I was thinking a thin wood panel might transfer less cold from the outside- but maybe it would just condense on the surface of the wood?

Edit- not my boat but they are all the same basically inside- you see the curved cabin ceiling meets the vertical surface where the potholes are, under that is a horizontal surface that extends from under the “wall” with the portholes to the top edge of the hull (there’s no seam there all Marshall’s cabin tops are bonded to the hull). That’s the spot.

Sounds like the underside of your decks are what's sweating and you have it in warm weather as well. I think the answer is better ventilation. Changing the air inside the cabin more often will help carry moist air out. You're right, the moisture is probably human caused.

Marshall 22 is a nice boat. I think there is one in my harbor but I can't recall if it has any cowl vents or other means of ventilation. If you're spending time overnight on the boat, I'd look into adding a cowl vent or two with dorade boxes. Next best would be a Nicro powered ventilator of some kind.

 

[Mr Fox]

i do have a nicor day night vent, and the cockpit doors are louvered, Maine gets a big drop in temp at night it’s a challenge! Maybe an additional dorade could help.