Condensed for your inconvenience

Phil Herring

Alien
Mar 25, 1997
4,918
- - Bainbridge Island
I don't know a boat owner who doesn't fight the good fight against condensation, the mother of mold, mildew, and soggy cushions.

Have you found any tricks to keep your cabin dry year-round?

moist.jpg
 
May 12, 2004
1,502
Hunter Cherubini 30 New Port Richey
Big problem here in Fl during the summer. No AC on board. I keep the head port open for fresh air circulation, a fan running and hatches open when I'm onboard, and a good water and bleach wipe down every so often. Oh, and a couple of well placed plastic containers to catch any drips from rain. Beyond that, I'm at the mercy of the humidity gods.
 

jwing

.
Jun 5, 2014
503
ODay Mariner Guntersville
The first step is to have a working knowledge of the science: Condensation is caused when a surface is colder than the dewpoint temperature of the air. So, there are only two choices: 1) increase the surface temperatures so that they are warmer than the dewpoint; 2) lower the dewpoint (that is: reduce the relative humidity by removing water from the air, aka dehumidifying).

I don't care how many people come after me and say that air movement eliminates condensation, it doesn't - unless the moving air is either warming surfaces or reducing the relative humidity. I'll tell you this: if air is trapped inside your boat, it will get hot during the day and water vapor will migrate from outside to inside. At night, as things cool down, the relative humidity inside the boat will be higher than the R.H. outside the boat. The water vapor will try to migrate back out, but if the surfaces are below the dewpoint, condensate will form on the inside. One way to mitigate this is to not trap air inside the boat. That's how ventilation works. It's not the velocity, it's pulling moisture-laden air out of the boat and replacing it with drier air.

Another approach is to reduce the heat gain inside the boat and reduce the heat loss outside the boat. The most obvious passive approach is to cover your boat to reduce solar gain and prevent radiation to the black night sky.
 
Sep 14, 2014
1,251
Catalina 22 Pensacola, Florida
Eleven really fat sponges stuck in bottom of compartments.
 
Jun 2, 2004
3,390
Hunter 23.5 Fort Walton Yacht Club, Florida
I found the solar powered fan and two 100 watt light bulbs take care of the issue for me.

I bought several cases of bulbs when this was still America and they let you have such a thing.
 
Nov 26, 2012
1,653
Hunter 34 Berkeley
Yes. A heater. The first thing I did was to get a working knowledge of the science. Then I bought a heater. I live in a cold damp place so the heater is what I need. If you live in a hot damp place you need A/C. The name of the game is to reduce the relative humidity. Anyway, I got a small electric heater that I keep on in the boat when I am not using it. Works great. Of course the boat has to be plugged in to shore power. I also have the solar vent going all the time.
 
Jan 25, 2011
2,391
S2 11.0A Anacortes, WA
What can I say...I don’t have the problem. Two dorades up front. One pointing fwd and one pointing aft.
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
I run an air conditioner on its own "dehumidifier" program when I am not there.
 
Sep 20, 2014
1,320
Rob Legg RL24 Chain O'Lakes
I don't care how many people come after me and say that air movement eliminates condensation, it doesn't - unless the moving air is either warming surfaces or reducing the relative humidity. I'll tell you this: if air is trapped inside your boat, it will get hot during the day and water vapor will migrate from outside to inside. At night, as things cool down, the relative humidity inside the boat will be higher than the R.H. outside the boat. The water vapor will try to migrate back out, but if the surfaces are below the dewpoint, condensate will form on the inside. One way to mitigate this is to not trap air inside the boat. That's how ventilation works. It's not the velocity, it's pulling moisture-laden air out of the boat and replacing it with drier air...
The purpose of a fan is to cause the boat surfaces to track the air temperature. If air is circulating, it will prevent significant temperature differential between the surfaces and the air.
 

TomY

Alden Forum Moderator
Jun 22, 2004
2,758
Alden 38' Challenger yawl Rockport Harbor
What can I say...I don’t have the problem. Two dorades up front. One pointing fwd and one pointing aft.
Same here. We have 4, 4 inch, and one, 3 inch cowl vent, most on dorade boxes, facing into the wind (boat is on a mooring all season).

Tons of air enters the anchor locker and midships. Lockers are left open in the galley area so the air moves through the cabin, engine area, under cockpit and through lockers, and exits 2 aft facing cowls.

With the hatches and companionway closed up (boat left on mooring), ventilation is through the cowls only. You can test to see that air is moving through the boat by holding your face in front of the aft facing cowls.


Our climate on the coast of Maine is pretty dry for starters, but some boats suffer from mold and mildew, especially in spring and fall. I think that is due to lack of ventilation.

The moving air is still wet, but the constant ventilation keeps the temperature of the surfaces even below, so condensation doesn't form(usually), in our climate. If mold or mildew does form because of conditions, if ventilation is thorough, it will dry up quickly.

At any rate, a well ventilated boat smells fresh when you open the hatch boards and go below. A poorly ventilated boat, just like a house, can smell 'off' when you enter.
 

jwing

.
Jun 5, 2014
503
ODay Mariner Guntersville
The purpose of a fan is to cause the boat surfaces to track the air temperature. If air is circulating, it will prevent significant temperature differential between the surfaces and the air.
Not really, but anyway, temperature difference is irrelevant to condensation formation. Condensation will form in air if the air drops below dewpoint temperature (ever seen a cloud?) Simply running a circulation fan in a closed space will not prevent mildew.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Geographical location of the boat makes some difference in how much condensate one has to deal with.

here in the NW, we had a problem and then we fixed it.
if one takes the time to really understand what causes the condensate, and has the means and ambition to remedy it PROPERLY, the first time, the problem will be gone.
too often people make a half a**ed attempt to stop the condensate problem, with poor results.... if they would understand the whys and hows of it, and then use that knowledge to put their heart and pocketbook into it, their problem will be gone forever... everything is a trade off, so you dont get something for nothing.

short of using a dehumidifier, the answer lies in fresh air movement in to the boat, which will displace the moisture heavy air and push it out of the boat... positive ventilation is much better than passive ventilation, and the use of a fan causes positive ventilation and a speed up of the process.... or when used inside the boat, it can move the stagnant air out of the corners and crevices within the boat, so that it can be displaced with fresh dryer air... dorade vents in the breeze is also a form of positive ventilation. without an outside air movement, dorades and open ports become passive ventilators.

if one is living on the boat (either for the weekend or long term), the ventilation into and out of the boat is even more important, but this can cause another problem, which is the loss of heat within the boat.... so then a DRY heat source is needed for comfort.

my fix was to install a Wallas heater overhead in the quarter berth, and ducted it to the v-berth.... the heater drew air in from outside, heated it and delivered it to the very front of the boat, which in turn pushed the moist air out and thru the small gaps in the sliding hatch... this stopped the condensation, AND made the boat smell fresher.
 
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Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
I don't know a boat owner who doesn't fight the good fight against condensation, the mother of mold, mildew, and soggy cushions.

Have you found any tricks to keep your cabin dry year-round?

View attachment 149139
In the Pacific NW the best solution for when you are on the boat is a forced air heater that pulls air from outside, heats it and pushes the cool moist interior air out of the boat. We often take a Thanksgiving cruise and have spent up to a week with rain every day and still had a dry boat. In the summer we run the heater for an hour every morning to dry out from the previous night. Solar vents keep up with the moisture when not aboard.
 
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Gene S

.
Nov 29, 2015
181
Delphia 37 Tacoma
I use an electric dehumidifier. The drain drips into the head sink. I keep the heat on and set to 52 to 55 degrees. Yes its cold and wet in Everett WA

Ken
What he said. My boat sits for a long time during the winter. I have one of those WM heaters set to 52-50° and there is no condensation anywhere. In the summer it's pretty dry. Now if I can get rid of the sea smell that builds up, I'll be happy.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Now if I can get rid of the sea smell that builds up, I'll be happy.
you can use a dehumidifier to remove the moisture from the air (when you have a power source) but without positive ventilation, smells will still build up AND any mold/mildew spores that may get a start, will stay trapped in the boat to multiply at will wherever they land in a crack or crevice where the moisture may be high enough for the spores to live...

a boat without adequate ventilation will always have a smell, and this smell will eventually permeate the upholstery, clothing, woodwork, books and any other porous surface or item. positive ventilation will keep the air changed out and much fresher, and in time the undesirable boat smell from all the porous surfaces will begin to lessen also.
 
Mar 26, 2011
3,401
Corsair F-24 MK I Deale, MD
Dehumidifier.

The solution is climate- and boat-specific. If the weather includes very cold water and warm humid warm air, more air just mean more condensation. If the boat is not cored or has metal hatches, that increases condensation. Most of the time ventilation helps, but I know from direct observation that some places are like a glass of ice water in summer; the drops form faster than you can wipe them away. If ventilation or a fan would prevent condensation, a dehumidifier would not work and an air conditioner would not draw condensate. So what works one place and one one boat may not work for the OP. It depends on the temperatures and the materials.

And no, you don't need an open window to prevent the build up of smells, and more than you do at home. Boats aren't that air tight. It also depends on whether the boat has leaks, how clean the bilge is, and if the head is well maintained. I've sealed up several boats and used dehumidifiers; if anything, the smell and freshness was better than with ventilation. So this cannot be an axiom either way.

It just depends on the thermodynamics of the boat and situation. There is no point in being adamant, only in trying alternatives until you find the best fit.
 
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