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Old 12-12-2019, 00:44   #31
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Re: How to keep mold out and the hull smelling good

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Please explain to me where the frost comes from on my windshield if cold air has no moisture?
Where do you experience 100% humidity with no moisture ?
I m in Alabama and I have to disagree with you.
You need to understand the difference between the amount of moisture in the air and relative humidity.

You cannot have 100% humidity with no moisture in the air, but cold air can only retain very small amounts of moisture, so therefore its relative humidity is high when only a small amount of water is present.

Frost is formed because the cold air cannot retain very much moisture. Once the saturation point is reached water will condense on any slightly colder surface.

The physics is quite simple, but counterintuitive. Once understood is explains exactly why water condenses and allows simple calculations that will show if a surface will become wet or not. Because it is counterintuitive many people do the wrong thing such as shutting out cold air because they wrongly believe it contains a lot of moisture.
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Old 12-12-2019, 01:21   #32
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Re: How to keep mold out and the hull smelling good

Dehumidifiers all the way. Got two going at the moment overwintering in WET WET WET corfu. Boat humidity when it started raining got to 85%, and you can't ventilate well because of the precip etc. The two units are pulling 16 liters of water out of the air EACH DAILY. But keeping the interior at a beautiful 40%. Worth every penny in terms of cash and storage space if you are wintering onboard with shore power.

Without shore power I'd be blasting the diesel heater. That'll dry you out well also.
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Old 12-12-2019, 01:58   #33
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Re: How to keep mold out and the hull smelling good

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Dehumidifiers all the way. Got two going at the moment overwintering in WET WET WET corfu. Boat humidity when it started raining got to 85%, and you can't ventilate well because of the precip etc
A system to provide adjustable ventilation that works even in heavy rain is worthwhile installing. This is one of the keys to avoiding condensation.

I have never used a dehumidifier but they receive good reviews (especially the desiccant types) from boats with mould/condensation problems. However, they do use a reasonable amount of power, so for many boats they are only a solution when shore power is available, although some boats use a short run time to reduce moisture with specific problems such as wet clothes hung inside, or prolonged propane cooking. One caution is they seem a common source of boat fires.
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Old 12-12-2019, 07:58   #34
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Re: How to keep mold out and the hull smelling good

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Originally Posted by noelex 77 View Post
You need to understand the difference between the amount of moisture in the air and relative humidity.

You cannot have 100% humidity with no moisture in the air, but cold air can only retain very small amounts of moisture, so therefore its relative humidity is high when only a small amount of water is present.

Frost is formed because the cold air cannot retain very much moisture. Once the saturation point is reached water will condense on any slightly colder surface.

The physics is quite simple, but counterintuitive. Once understood is explains exactly why water condenses and allows simple calculations that will show if a surface will become wet or not. Because it is counterintuitive many people do the wrong thing such as shutting out cold air because they wrongly believe it contains a lot of moisture.
Tell me where you studied this and point out the science.
Some cold air has moisture and some doesnít. Being counterintuitive means squat in your explanation. Its like arguing about climate change without facts not fiction or a political narrative.
Frost is from moisture in the air . If the frost is not there , theres no moisture. Frost forms 32f andbelow, condensate at temps above. Thatís physics.
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Old 12-12-2019, 08:23   #35
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Re: How to keep mold out and the hull smelling good

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Some cold air has moisture and some doesn’t.
True, but the maximum amount of moisture cold air can hold even when 100% saturated is relatively low.
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Old 12-12-2019, 08:32   #36
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Re: How to keep mold out and the hull smelling good

This graph from:
https://www.wikiwand.com/en/Relative_humidity

Shows how the amount of water that air can retain decreases dramatically as the temperature drops. Cold air cannot hold much moisture.

The red line is for 100% relative humidity. The air cannot hold more water than this.

There are numerous identical graphs, as the science is well understood.
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Old 12-12-2019, 13:31   #37
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Re: How to keep mold out and the hull smelling good

Warm air CAN hold more moisture than cold - reference above graph.

Relative humidity is how "full" the air is. Air, at a given temperature can hold X amount of gaseous water. %RH is % of X that is actually in the air. 40 degree C air can hold 50 grams of water per kilogram. If it is 75% relative humidity, there is actually 37.5 grams of water per kg. When relative humidity "exceeds" 100%, the excess forms clouds, rain, or snow (can't be more than 100%).

Condensate forms on your cold beer because it is cold - nearby air gets cooled (and unfortunately warms your beer), and the relative humidity "exceeds" 100% and the water becomes liquid - surface tension puts the water on the can.

Relative humidity determines how fast water evaporates. Air is like a sponge, once it is "full" of water it won't hold anymore. A dry sponge will do a better job of mopping up spilled beer than a wet one. You can't hang your laundry out to dry on a 100% humid day! (Note, 100% humidity is relatively unusual, think fog.)

Specific humidity is the amount of moisture in the air - grams per kg in the above graph. When air goes from cold to hot, the specific humidity does not change (no water is added or removed) - but because warm air can hold more water, the relative humidity reduces. That is why warming air helps it dry things; heating in a laundry dryer, for example. Hot hair driers. Ovens. Etc.

The water in air is always gaseous, independent of temperature. The phase only changes from gas to liquid or solid when it condenses. If it is cold out, there may be frost on your (even colder) windshield. Ice, in turn, "evaporates" into water vapor at cold temperatures, just like water (sublimation). The rate of sublimation is a function of the relative humidity.

Don't spill your beer, drink it before it gets warm.

Wishing all smooth odor-free sailing!
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Old 12-12-2019, 13:36   #38
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Re: How to keep mold out and the hull smelling good

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Originally Posted by noelex 77 View Post
True, but the maximum amount of moisture cold air can hold even when 100% saturated is relatively low.
I have a few unheated but closed up houses nearby, outside temps fluctuating a lot between above and below freezing.

When the inside temperature is colder than that outside, the walls and especially the windows are streaming with water running down from condensation.

As in many liters' worth.

Ventilation is one solution when heating is not possible.
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Old 13-12-2019, 08:06   #39
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Re: How to keep mold out and the hull smelling good

Quote:
Originally Posted by noelex 77 View Post
This graph from:
https://www.wikiwand.com/en/Relative_humidity

Shows how the amount of water that air can retain decreases dramatically as the temperature drops. Cold air cannot hold much moisture.

The red line is for 100% relative humidity. The air cannot hold more water than this.

There are numerous identical graphs, as the science is well understood.
I understand relative humidity quite well.
I think for you to understand the point that is given in this discussion , is that cold can be 50 or -50 .
Someone blowing air at a different temp experiences different results. No wiki chart required.
The common sense portion of all the scientific hubub is remove the moisture. The means justifies end and vice versa.
Thats applied science.
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Old 16-12-2019, 07:42   #40
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Re: How to keep mold out and the hull smelling good

Dehumidifier
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Old 16-12-2019, 08:14   #41
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Re: How to keep mold out and the hull smelling good

following...at least the practical side of the discussion.
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Old 16-12-2019, 08:59   #42
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Re: How to keep mold out and the hull smelling good

Moisture in a metal or plastic boat can be found in any wood used for mounting , backing pads or internal structure that has been very wet.

Even rot that does not smell can add moisture on an almost constant basis.

Find any rotten wood and change it. Old boat stink ,,,gone..
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Old 16-12-2019, 09:15   #43
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Re: How to keep mold out and the hull smelling good

You have gotten some input that may or may not help.

Right after we bought our boat I added to the 2 deck hatches, 1 over the V-berth and the other in our aft SR, solar vents.

They are 3 1/2" (4 1/2" are available but wouldn't fit on our hatches) and are powered by the sun charging the battery to run the fan.

I have 1 unit drawing air in and the other pulling air out (2 separate blades to the fan come with the unit).

Even when laid up for the winter and the charge in the batteries run down, the opening allows the flow of air (ventilation) to circulate thru the boat.

We've owned the boat since '10 and have never run a dehumidifier or any other electrical piece of equipment when the boat was put up for the winter. We also were on the Chesapeake from '10 to '16, before we started the Loop and before we retired so the boat would be closed up during the cruising season (May to Nov) during the week while we were working. Never had mold or mildew.

I've attached a picture of our boat, overhead shot, to see the hatches (the aft is in the sundeck below the roof on the stbd side).

Good luck with your issue. This has worked for us.
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Old 16-12-2019, 09:29   #44
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Re: How to keep mold out and the hull smelling good

An old sailing friend, the designer builder and author Thomas Firth Jones who made numerous trans Atlantic voyages in small craft, once shared his observations about mold in boats: Tom told me sea water is loaded with proteins and when inside your boat provides the nutrients for mold growth. Likewise most detergents are biodegradable and provide nutrient. Keep the interior clean and dry!

In terms of eradication he suggested ethylene glycol prevents mold growth. Borax and of course white and red lead compounds are excellent inhibitors.

In my experience boats and other structures with inaccessable areas can be made fresh using ozone generators. The ozone penetrates all air spaces to oxidize and kill molds and spores. Ozone does not prevent reinfection. Only toxics or removing nutrients and/or moisture will keep things fresh. Dehumidifiers or AC are excellent for storage prevention


weather gear">Foul weather gear is a related topic.


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Old 16-12-2019, 10:37   #45
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Re: How to keep mold out and the hull smelling good

Generally speaking, does our breath cause the production of more moisture accumulation within the cabin of a sailboat? Iíve noticed that after sleeping on board, in the early morning, there seems to be a moderately significant amount of condensation on the cabin ceiling. We use a dehumidifier that is constantly running when docked and we have a solar powered ventilation fan that obviously doesnít function for long when the sun goes down. The outside temperature varies, at night between 45 degrees F and 55 degrees F year round. In addition, we have adequate hatches and appropriate vent on the companionway hatch when in place at night. We are not live aboard folks as we use our boat for two to three days at a time every three to four weeks during all seasons of the year along the central California coast. Any suggestions are welcomed.
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