Condensation on boats.

[Binman]

Why do I read about condensation on boats a lot on this forum, what boats does it mainly effect, if it's not on the headlining it's under mattresses, fortunately my boat suffers none of this. Surly the answer is more ventilation, or am I missing something?

 

[Wandering Star]

2016 will be the year for no boat condensation problems

Happy New Year Mr Binman.

 

[Binman]

Happy new year to you as well Wandering star.

 

[[70521]]

I put it down to modern boats being hermetically sealed. I have every hatch open for as long as I can and never have a problem.

 

[Halo]

There were a lot of threads about de humidifiers. These eliminate condensation and stop mould forming
All the best for 2016
Martin

 

[Binman]

But why do we need them? Happy new year.

 

[pmagowan]

But why do we need them? Happy new year.

Basically condensation occurs when warm wet air hits a cold surface. The air cools and can hold less water. In a boat there is a small space full of humans and all the moisture they create. They like warmth so you end up with warm wet air. The boat sits in a cold liquid and often a cold environment so the surfaces get cold and thus condensation occurs.

To prevent it you can either:
1) dry the air with a dehumidifier
2) insulate the surfaces so they don't get cold
3) ventilate to replace the warm wet air with some cold dry air.

There are issues with all of these:
1) requires electric and emptying of the dehumidifier. It is only effective if you can lower the relative humidity of the air sufficiently so ideally you don't want much ventilation or standing water.
2) is sometimes difficult to retrofit and requires close attention to detail. Insulation needs to be water vapour impervious or have a vapour barrier otherwise water will pass through it and condense on the cold side. Any uninsulated areas will be effected worse than before.
3) is relatively simple but outside air can be warm and wet and still condense on the hull where there is a lower temperature such as below the waterline. Also, ventilation makes the inside environment cold and extra heating is required to make it comfortable therefore it is inefficient.

I am planing a solution which involves mechanical ventilation with heat recovery. This would be in a well insulated and airtight boat. Dry fresh air would be brought in via the blown air heating system. Wet stale air would be extracted by a similar system of ducts from the heads, wet locker, cabins and galley. The heat in the extracted air would be recovered and passed to the incoming air acting in much the same way as a dehumidifier. A low power fan would be all that is needed to run it.

 

[Binman]

Is this a bigger problem on boats over say 30ft, where I assume it's harder to control the warming up and cooling down time. Mattress material and coverings must come into it, all my cushions and mattresses are covered in material that is breathable,I surpluses on a small 7m craft like mine, the change in air temperature is less dramatic, then say 30/50 ft craft. When sailing in cold windy conditions, just coming into the cabin feels warm, if dressed properly, with out any heating.i do light a oil lamp I have, and using the hob,is enough to be comfortable, the number of people also has a benefit, also I have no hot steamy water to dissipate, Drying wet clothing would be another source of condensation, what would you use?
The sort of damp atmosphere that many struggle with also brings or can bring health problems, for those liveaboards. At this present time, what is regarded as the most suitable method to banish condensation and be comfortable at the same time.

 

[thinwater]

Binman: I don't think you have really read the threads, reading between the lines. Most of these people either live on the boat or cruise significantly. They run heat. They contribute moisture with respiration and sweat (3 pints/person-day), they cook, and they bathe. All included, the probably add at least 2 quarts/person-day. If they wore more clothes and day sailed only they would not be having this discussion. Pmagomen basically covered it; you must keep the dew point below the temperature of coldest surface surface by either (a) dehumidifying, (b) heat and ventilate which is wasteful, or (c) insulate to keep the surfaces warmer. (c) is most energy efficient, but all 3 work. Generally, a combination is required, so there are multiple right answers.

Yes, it is a little complicated, like anchoring.

 

[Binman]

Thanks for that,thin water, I was being guided and coming to the same conclusion.your two points taken in the first sentence, next time the question arises I will ask those two question, and find out if it bares its self out.