curing condensation

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drawkins

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How can I mitigate the problems of condensation in an unlined hull?International used to market a paint,was it any good?
should I plan to line the hull in the winter.
It is bad behind the backrests on the quarter berths.
I have put in a deck ventilator and another in the hatch washboard
any suggestions welcome
 
need to know more details of the boat construction, steel, grp, etc, and the areas where you operate, N Scotland, Med.

Generally, it's a matter of ventilation; bringing in lots of warm, dry air to replace cold, damp air and to warm hull and fittings above the point where the humidity in the air can condense on them. Dehumidifiers are often used in uninhabited boats to reduce the levels of RH.

The key to handling condensation is understanding that wide variations in temperature with high rel humid (RH%) will cause water to appear on surfaces. Preventing a very cold steel hull from contacting warm wet air by insulation is another strategy.
 
I think you're referring to 'Corkon' - oddly enough, paint with cork granules in it. 'Twas better than nothing. But still dripped.

Years later I had an X-Yacht. Foam sandwich deck - except at the junctions between the horizontal and vertical surfaces, which were solid - guess where the drips started?

It's fairly simple Thermodynamics. You need the through flow of air to exceed the rate at which the deck structure can remove heat from the internal surface - more insulation, less through flow, and vice versa.

I'd be going for the cheap option - 2 to 3mm expanded foam, or a carpet type covering, stuck up with Thixofix.
 
As others have said, ventilation is a key factor but in damp environments like the UK a dehumidifier is magic. Once you've had one you'll never want to be without -- everything warm and bone-dry. Makes you happy to leave the bedding and towels on board and go sailing in the winter.
 
Fine if you are in a marina, with access to shore power, but thousands of sailors aren't. /forums/images/graemlins/smile.gif
 
Cure ? There is no cure no matter what anyone claims. What there is - is control of it to minimise effects.

Ventilation - doesn't have to be huge volumes of air passing through - but a reasonable steady flow of natural air. If surfaces and air are in relative harmonised temp (ambient) condensation is reduced. Alter that balance and bingo water appears.
Surface structure affects how the water condensing out affects around it .. hard surfaces will have water runs and drips, carpet tiles / matt surfaces will generally 'lose' the water in the uneven surface.
Contact of items with surfaces will cause wet patches (remember camping ? and being told DON'T TOUCH INSIDE OF TENT !). So keep items like mattresses, lifejackets, cushions etc. from contacting underdeck / hull / surfaces ...

I used to leave my boat with all gear on year after year afloat - use being only a few weeks a year on return to UK. I never had problem with condensation if I remembered the above. No de-humidifiers or heaters used.
Now with boat out here in Baltic, I only use small anti-frost heaters for real cold winters to try and reduce frozen conditions inside.

Boats 'sweat' especially later with extensive mouldings - the expanse of gloossy surfaces are prime condensation creators - so air movement even slow is needed. Older boats where bare GRP / wood also suffer, older with partial internal mouldings seem to fair better.

So IMHO - first of all careful thought of how to ventilate the boat, don't forget wet-hanging space and WC compartment, lockers that water can collect in and increase internal humidity - open them up, move items away from touching surfaces .... if that doesn't have desired effect - then start to look at additional electric measures. It is worth looking at carpet tiles to line a hull at sides .. my boat has them and it's very successful.

I've heard theories of applying contact glue for tiles ... in vertical lines only - NOT spread around ... supposed to allow moisture to migrate along the unglued areas to clear ... maybe works, maybe not ? But I know that my tiles are dry to touch ...
 
Unlike most of International's stuff, the 'Anti-condensation' paint was rubbish. It may well have had 'added cork', but is still always got covered in condensation which, as usual, resulted in mildew. /forums/images/graemlins/frown.gif

The problem was then worse, because trying to the clean mildrew from a textured surface, was almost impossible. /forums/images/graemlins/mad.gif

Others are suggesting alternatives, and I suspect that whatever you choose, it would be better. Anyway, I'm not even sure they still make it.
 
Thanks everyone for replies.
boat in Ireland,type GRP.sailing in fresh water mainly.
difficult to bring in lots of warm dry air with the humidty readings we have been having.
was thinking along the lines of double glazing units thats why I asked about linings.
never remember a big problem on my Landamore's Hustler
guess I will have to move the bunk cushions etc out and just go sailing...now
 
[ QUOTE ]
Cure ? There is no cure no matter what anyone claims. What there is - is control of it to minimise effects.



[/ QUOTE ]

Technically you are correct but boat wise the nearest you will get is with a sandwich hull or a build like a Sadler. No perceptable condensation in our Starlight even in the coldest weather
 
I don't think you have managed to create enough air flow through your boat. You might consider increasing the flow of air by adding one or two solar powered extractor ventilators fitted at the other end to your air intake. You could also fit another solar powered ventilator, this one though in the "air flowing-in" mode.

Roger
 
try and arange that one ventilator is higher than the other, if this is not possible, assuming you have two , then temporarily fit a plastic pipe to one ( sealed to the inlet with duck tape or whatever you choose) getting the end as low as possible, this will I think you will find,work ok.
 
It’s good to have an understanding of how condensation forms, then we can workout remedies and some responses above have certainly done this. I expect they all know the following, I will try not to go too technical, so those that know the difference between percentage saturation and relative humidity hold fire, I am trying to explain the process somewhat simply for those that still don’t quite understand it, here is my attempt:

We generally consider two temperature properties of air, dry-bulb temp and wet-bulb temp. The difference between them tells us the percentage saturation or humidity level in the air.

In the old days (my day) the temperatures were taken by a whirling hygrometer, which comprises two dry-bulb thermometers, both rotated in the air, but one had a wet wick covering its bulb (hence wet-bulb temp), water evaporated from the wick only if the air that it rotated in was not 100% saturated (100% humidity). This then cooled the wick and therefore the wet-bulb temp was usually lower than the dry-bulb temp, but the two temps were the same at 100% humidity, because no water could evaporate and cool the wick.

Air at a given temp and humidity (atmospheric pressure) can only hold a certain amount of water. This temp is known as its dew-point temp, at 21C 100% RH any surface below 21C would force the air to cool and hence it must release its moisture in the form of condensation to form on the colder surface.

So, there are several ways to reduce condensation:

1) A dehumidifier is very effective, it forces the air over a very cold surface, moisture is removed in the form of condensation and the air that leaves the humidifier holds less water, when it meets the warmer air in the room, it quickly heats-up, it can now hold lots more moisture, which is absorbed from the air in the room and the room RH therefore drops. This then reduces its dew-point temp, so surfaces that may have caused condensation don’t because the surface is now warmer than the dew-point temp of the air!

2) Insulation and barriers, can be effective, they simply increase the inner surface temp above the dew-point temp of the air. But remember this dew-point temp can increase as the humidity in the air increases, so sometimes unless you get the insulation level right (unlikely with any cork paint) you may still get some condensation.

3) Ventilation, what this does is to dilute the moist air in the room (higher due to moisture laden processes such as humans, kettle, etc). With a room at say 70%RH, in summer external air generally is around 50%RH, if we can bring enough of this air through the space, the air in the room would drop in RH to approach 50%, hence the dew-point temp drops and its then unlikely any surfaces will be cold enough to form condensation.

So there you have it, hope the above helps.

I would probably opt for better ventilation first, then perhaps try some insulation, but if you have a real problem electrical dehumidifiers (although I am told some dessicant pots can sometimes be effective).

Not trying to be clever, just trying to help to explain! But probably failed dismally....... /forums/images/graemlins/cool.gif
 
We have had success with a additive to paint, working in a similar way to the cork in the paint.

Hollow glass beads canbe used to thicken epoxy.

The hollow beads added to the paint do work for us in the humid N.W.

Three coats on bare metal uninsulated metal close to the hatches has stopped winter condensation.

The rest of the boat has 3 cms of fire retardant polyurethane foam covered with the same paint including the glass beads as fire protection.
 
I like the idea, but this then approximates an air gap with added vapour barrier, have you run a condensation calc? I would normally use Hevacomp MAT for non-marine applications. I would be interested to see your graph showing dry and wet bulb temps through the structure. Most interesting. /forums/images/graemlins/cool.gif
 
I am trying to draw conclusions from the very helpful advice.
First.I should improve the ventilation.It is quite difficult to get a ventilator into the stern of the boat unless it is vertical in the cockpit.I am looking at solar powered fans
second.it would seem that I really have a floating dehumidifer as the main condensation is taking place where the hull experiences a sharp drop in temperature where the water line is.
so perhaps I should insulate at the ,and below the water line with a vapour barrier
thirdly keep cushions etc off uninsulated surfaces.
fourthly buy waterproof pyjamas
 
I covered the vertical surfaces of the forecabin with 12mm PU foam slab and a single layer of CSM finished with a flow coat. This was about 5 yhears ago and it worked well. I am refitting at present and as part of it I intend to do the quarter berth and main cabin. This is only above the water line. The only condensation comes from the metal of the hatch and windows. The foam was put on using thickened polyester.
 
Getting back to the anti-condensation paint produced by International, I agree with the people who have tried it and not found it very effective. In my opinion the problem was the particles in it were too small. Years ago when I was in the Royal Navy we used an anti-condensation paint which was very effective and contained large particles of cork. I have not been able to find a supplier of it, but I know it used to work very well.
 
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