Double glazing

[US Marines]

So does this imply that if you sealed up all the vents to prevent any moist air entering an empty, unattended boat, then the temperature-cycles which cause condensation to form on the glass and run away through the drip channels, would effectively turn the whole boat into a giant self-dehumidifier - become drier and drier inside until there was no further condensation?

Ok - let's go back to first principles....

 

Absolute Humidity (AH) = amount of water vapour in the air

Relative Humidity (RH) = how close the air is to saturation

Dew Point Temperature (DPT) = the temperature at which condensation occurs (this is normally also just below the temperature at which the air becomes saturated)

 

Warm air can contain more water vapour than cold air.

 

For all intents and purposes, air always has some water vapour in it.

 

Our experience of 'humid' conditions is related to high RH, not AH.

 

If you cool a given parcel of air without adding any more water vapour, its RH goes up - so the air becomes more humid - but its AH (i.e. the actual amount of water vapour in the air, remains the same).

 

If you cool a parcel of air down far enough its RH will reach 100% (saturation), it will reach its DPT and condensation will occur.

 

If you warm up a parcel of air without adding any more water vapour, its RH goes down - so the air becomes less humid - but its AH remains the same.

 

If you add water vapour to air, you increase its AH. Therefore, its DPT will also increase and you won't need to cool it so far as before, in order for condensation to occur.

 

Therefore, if you warm up air but also add water vapour, its RH might remain constant or even reduce during the period when it is warm, but its DPT will be higher than before so, when it cools down again later, it won't need to get so cold as it would have needed to get previously, before condensation starts to take place.

 

If you take water vapour out of air, you reduce its AH. Therefore, its DPT will be lowered and you will need to cool it further than you did previously before condensation occurs.

 

If you sealed your boat up and water condensed out on the windows one morning it would normally evaporate back into the air when temperatures increased during the day and the RH reduced. So, assuming that the daily weather pattern and diurnal max and min temps remained constant, you would just get a cycle of condensation and evaporation.

 

If however, you removed the liquid water that condensed out so that it did not evaporate back into the air - the AH of the air would go down and the following morning would need to be a little bit colder before condensation occurred. If it did keep getting cold enough each morning for condensation to occur, eventually almost all of the water vapour would be removed from the air. However, temps would need to get very cold indeed (far below zero degrees Celsius) before this occurred.

 

Does any of this help or is it all gobbledygook ?

[Keeping Up]

Not gobbledegook, that's exactly the reasoning I went through mentally before posting my question

[Nickhlx]

Not gobbledegook, that's exactly the reasoning I went through mentally before posting my question

 

Yes - I say you are right - if no moisture is entering the boat ( obviously a little damp air may well do but this is small in comparison with what is being taken out of the system by the "de-humidifier effect" of the windows)

If the windows discharging their condensate to the outside, moisture is effectively being taken out of the boat.

 

I would think though, that without a little heat input, the system will settle down to a mean humidity, which might be still a little too high and allow mildew to form in the colder pockets around the boat.

 

Definitely ventilation rather than a static / sealed situation is to be preferred as wood and furnishings will give up their natural moisture slowly to the surrounding atmosphere.

 

Nick

[Pretty Funked Up]

Thanks Roger, all very helpful stuff

 

The stops on my window are rivetted onto frame but i am lucky as the dont stick out past the frame.

Can i just confirm... you stick the film to the wooden frame (after plugging holes and removing all moisture.??

 

thanks again this should be really helpful for me.

[Roger Gunkel]

Thanks Roger, all very helpful stuff

 

The stops on my window are rivetted onto frame but i am lucky as the dont stick out past the frame.

Can i just confirm... you stick the film to the wooden frame (after plugging holes and removing all moisture.??

 

thanks again this should be really helpful for me.

 

Yes as simple as that

 

Mine have been done a couple of days now and although I know the weather has been slightly milder, still no condensation and we have noticed we are using less fuel and keeping the fire shut right down. The whole boat also feels more comfortable.

 

Roger

[Pretty Funked Up]

I went to wickes and got a pack. £6.50 - I found i could only do 4 out of the 5 windows, in the living area, no matter how much i rearranged the plastic in relation to the windows.

 

Even though i only did 4 windows the boat felt instanly warmer, i am pretty sure this is from the hairdryer going flat out for 40mins

 

However i look forward to testing this stuff out through the night

[Pretty Funked Up]

Well, ive learnt 3 things with this window film stuff....

 

1. It does a very good job of stopping draughts

2. My window frames are definitely not sealed to the hull very well

3. The tape supplied it really useless, although it does stick to itself pretty well

 

[Andy Woods]

Same here....

 

Managed to do four of my windows, made a hell of a difference to the draughts and the film went smooth and clear when heated.

Following day half the film had come away from the windows as the double sided tape supplied is rubbish!

 

Have now ordered some 'industrial strength' double sided tape from fleabay and will redo the windows when it arrrives.

 

Hopefully this will cure the problem as the film worked well when in place.

[Roger Gunkel]

The stuff I bought last year, had really poor tape which I had to replace with better quality. The pack I bought this year which included the tape, has been really good and has stayed stuck firmly on all the windows. Nearly 3 weeks now and still giving good results. Persevere with the better tape, its well worth it for minimum cost. Its also worth noting that the tape will stick to the frame better if the frame is not cold when you apply it.

 

Edited to say that I have found a company that can supply 3mm thick acrylic sheet to cover my 42" x 22" frames for about £16 each. Because the results with the film have been so good, I have decided to start using the rigid sheet on a simple rubber surround, with turn buttons to hold it in place. The acrylic will also give better thermal insulation than the film, so should be even better still, plus easy to remove and re-use.

 

Roger

Edited December 14, 2008 by Roger Gunkel

[Sverre Magnus]

The stuff I bought last year, had really poor tape which I had to replace with better quality. The pack I bought this year which included the tape, has been really good and has stayed stuck firmly on all the windows. Nearly 3 weeks now and still giving good results. Persevere with the better tape, its well worth it for minimum cost. Its also worth noting that the tape will stick to the frame better if the frame is not cold when you apply it.

 

Edited to say that I have found a company that can supply 3mm thick acrylic sheet to cover my 42" x 22" frames for about £16 each. Because the results with the film have been so good, I have decided to start using the rigid sheet on a simple rubber surround, with turn buttons to hold it in place. The acrylic will also give better thermal insulation than the film, so should be even better still, plus easy to remove and re-use.

 

Roger

 

Just had to register at this forum because of the discussions on double glazing. I have been through all this - both with my previous boat, an LM-27 and now with my current project - restoring an old Fjord MS33. This is a boat intended for all year use - in fact my wife and me spent this Christmas Hollidays in the Oslo Fjord with -9 degs C and solid ice around the boat. Apart from 10mm to 20mm foam insulation all over the boat - the double windows made the boat extremely dry and comfortable.

 

For the MS33 i have attached 5mm acrylic sheets to the metal frames by using 3M double sided tape - 10mm wide and clear. This gives approx 6mm spacing. As we all know there will allways be some moisture in the air. If I could find a source for nitrogene gas I would have tried to replace the air between the window sides with gas - as they do with binoculars and some electronic equipment. But no luck there - instead I put some drinking straws filled with silica gel between the sides. But still there is a tendency to condensation building up at the inside - looks like small leaks in the outside metal frame.

 

Due to mechanical reasons the windows in front of the dog house had to be done differently. Instead of attaching the acrylic sheets straight onto the metal frame I made a 10mm wide frame of the acrylic and glued this to the window instead of the metal frame, and then put the 5mm acrylic sheet onto this frame (with the silica filled drinking straws between). Corners of the frame sealed with hot glue. These windows are still condensation free - and these are the important ones for navigation and lookout.

 

Another thing that is important is to get the windows 110% clean and dry (heated by a heat gun - careful!) - condensation starts at areas that is not perfectly clean.

 

If you can find a 5mm acrylic sheet instead of 3mm (I have used both) you wil see a surface temp difference!

 

Condensation or not - I would never go back to single glaze windows!

 

-Sverre

[Brinsail]

Last time I did it, I heated it up with a hairdryer and it came off quite easily. Took the residue off with meths. I'll find out again next Spring, as I just finished the rest of my windows about an hour ago.Took 90 minutes for the last 5 windows.

 

Roger

 

I've used the Wilko's brand plastic seal on very drafty patio doors in the house. It worked a treat to keep heat in. And the sticky tape even came off the gloss paint (with a little persuasion & kitchen cleaner) without damaging the paint.

 

I've got louvred windows on the boat which are really drafty. So much so that I made acrylic inserts with discrete low-profile handles, and latched into the stainless steel frames on plastic clips. (All items you could buy from Wickes, B&Q or Homebase).

If you fancy doing this I found through trial & much error that easiest way to 'cut' acrylic without shattering it is an angle-grinder with a very thin blade - go slowly in straight lines and it melts it. However Safety first:- essential you still use goggles and ear plugs.

 

I went to this trouble as the plastic film added a kind of fuzziness to the view, but I have to say the plastic film is by far the best draft-excluder.