condensation in sealed "water tight" hulls

Discussion in 'Boat Design' started by jedkins, Dec 29, 2006.

  1. jedkins
    Joined: Jul 2006
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: phuket

    jedkins Junior Member

    Is it possible for condensation to form in sealed air and water tight hulls? I am thinking specifically of beach cat hulls and trimaram amas.

    I am building a 20' trimaran and would like to completely seal the ama hulls whereby sea or rain water cannot enter. However, I am concerned that from experience with beach cats such as Hobies that there always seems to be some water within the hulls. I 've had similar experience with ama hulls. The hulls seem to be sealed but there it is - a little bit of water - is there any possibility its condensation or must it always be from a leak? Thanks for any advice
     
  2. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    If you fill the interior with foam it might stay dry , although the foam has weight .

    FF
     
  3. jedkins
    Joined: Jul 2006
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: phuket

    jedkins Junior Member

    Unfortunately I dont want the extra weight but I wonder what causes the water to form in the first place...?
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 481, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Temperature and humidly changes causes moisture in the air to condense and evaporate repeatedly each day. You could try an inert gas like argon, but keeping it truly vapor tight would prove troublesome.
     
  5. longliner45
    Joined: Dec 2005
    Posts: 1,629
    Likes: 73, Points: 0, Legacy Rep: 505
    Location: Ohio

    longliner45 Senior Member

    polyuethane foam will absorb moister after time,,and need periodic replacement
     
  6. Frosty

    Frosty Previous Member

    If its sealed then how do you know there is water in there? I guess you must have an access hatch!!!!!! Probably that leaks a bit, especially as the day cools and the air inside contracts.

    A little bit of water is not normaly a problem is it? unless you are building in steel.
     
  7. jedkins
    Joined: Jul 2006
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: phuket

    jedkins Junior Member

    Yes, That's why I dont a hatch - they always seem to leak. !!(actually a beckton plate) . Water left in the bilges of a wood boat will cause a problem eventually as it obviously causes rot over time. And in Amas, because of the compartmentized bulkhead arrangement water is often difficult to spot unless many plates are installed in deck. Which is a catch 22 as they tend to leak.!

    Getting back to my question - Does condensation occur in seal hulls like Amas ? I wonder if anyone can give me a answer to that specific question?

     
  8. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    If you fill the hull with cold dry air and manage to make it not only water tight, but diffusin tight, then no water will condensate as long as the temperature is allways higher than it was when you sealed it...

    But this is theory, I think it's impossible to make it "diffusion tight".
     
  9. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    This is pretty much true. An enclosed volume in a humid environment that has repeaded daily temperature cycles will "pump" moisture vapor through the walls unless the walls are 100% impermeable. It may take many years but will happen.

    That is the theory. I have had no problem with air tanks built of plywood and well coated with epoxy over decades of use.
     
    1 person likes this.
  10. jfblouin
    Joined: Sep 2004
    Posts: 163
    Likes: 1, Points: 0, Legacy Rep: 24
    Location: Chandler(Gaspesie) Quebec

    jfblouin Senior Member

    I'm building a boat with 24 air and water tight compartments (I assume). The biggest one is .25 m3 (9 CuFT). They are sealed with Epoxy. Somes sections have fiberglass also. But I live in Canada and temperature vary for -35C to +35C (-30F to +95F). With this calculator http://www.cactus2000.de/uk/unit/masshum.shtml I calculate that if I seal the compartment with 50% humidity at 15C (60F) I capture 6.4 gr (less than .25 oz) of water. If temperature drop to -35C (-30F) 6.2gr of water (or 6.2 ml) will condensate in compartment. If I can seal at 0 C (32F) I capture only 2.4 gr of water so only 2.2 gr can condensate at -35C.

    It is not a lot of water.

    The compartment need to be really water and air sealled because if new humid air can enter in the compartment at each temperature variation (by variation of air volume) or each variation in air pressure, a lot of water can be accumulate in compartment.
     
  11. Man Overboard
    Joined: Oct 2006
    Posts: 246
    Likes: 13, Points: 0, Legacy Rep: 129
    Location: Wisconsin

    Man Overboard Tom Fugate

    If you manage to get a perfectly tight container, you can still get water in the container by way of vapor pressure. To give an example of how powerful vapor pressure is; we have all seen cars that have rust that has formed underneath the paint, causing the paint to bubble. This is not necessarily due to rain, but vapor pressure within the air itself which forces minute molecules of water through the paint where it collects in high concentrations in the pores of the mettle substrate. (As a vapor) With changes in temperature the vapor will condensate into water. You may be able to get around the problem by slightly pressurizing the compartment. A gauge and a location on the compartment for filling with air would do. If you are building with a composite material, than epoxy is the best at reducing to a minimum the effects of vapor pressure.
     
  12. jedkins
    Joined: Jul 2006
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: phuket

    jedkins Junior Member

    Thanks for your comments. I live in the tropics where the day and night temperature rarely deviates between 27-34c. I am not sure abt our sea temperatures but the water is never very "cold" . However, Humidity is always very high. My amas are ply and are complety sealed with epoxy/glass. I guess I have a sealed area of abt 40 cubic feet. I will try the calcultor you mentioned to see if I can work out how much water I might capture.

     
  13. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    Drive up in the mointains, fill the hulls with cool dry air (add a little preassure), seal it and drive home :)
     
  14. jedkins
    Joined: Jul 2006
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 9
    Location: phuket

    jedkins Junior Member

    No mountains or cool dry air here in Phuket Thailand.......
     

  15. Man Overboard
    Joined: Oct 2006
    Posts: 246
    Likes: 13, Points: 0, Legacy Rep: 129
    Location: Wisconsin

    Man Overboard Tom Fugate

    You can make a home-made condensation trap by coiling up an airline hose and stuffing it into a bucket of ice water; after the line passes through the ice water, run it into a small pressure tank. Preferably one with a drain cock. If you can find an old junk truck in your area (one with air brakes) there will be a small tank just like what I describe on the truck somewhere. This setup will also give you dry air for any kind of spray applications you might be using during construction.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.