1956 20' Holiday - Dehumidifier????

Discussion in 'Wooden Boat Building and Restoration' started by 1956Holiday, Jun 4, 2011.

  1. 1956Holiday
    Joined: Jan 2011
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    Location: Prospect, KY

    1956Holiday Newbie

    Hello,

    Newbie is about ready to put his boat in the water..............

    I live in Louisville, KY. Boat will be on the Ohio. It is extremely hot and humid in the summer.

    Bought a slip, but it is not covered. The slip has electric and I was thinking about a standard mooring cover and plugging in a dehumidifier. I am concerned about humidity promoting rot, mold and blistering the finish.

    Conflicted here because I assume you want the humidity to keep the boat swollen. Also, if it makes sense should I let the water drain to the bilge or over the side. Draining to the bilge seems like a never ending circle - water turns into humidity, dehumidified, dropped back to the bilge, etc.

    Thanks for any help.

    PS: I am going to leave her on the trailer until I am sure the pumps will keep up/stop before I take her to the slip.
     
    Last edited: Jun 5, 2011
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A dehumidifier can prevent mold in the upholstery, but I doubt it can harm the wood.

    I use a powerful dehumidifier in a holiday apartment. It does prevent mold by keeping the air dry, but it cannot extract moisture from within the walls.
     
  3. Stumble
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    Location: New Orleans

    Stumble Senior Member

    I would recommend a AC instead of a dehumidifier. It will also do a good job of keeping the humidity down, plus when you show up to work on the boat during the summer it is bearable downstairs.

    There are really three types of AC's that can be considered. The first is a marine AC unit, but these are very expensive, and require new through hulls in the boat. The other option is a cheap window unit from Lowes. These typically will slide into the hatch, and work great but have to be removed every time you head out.

    Finally for a bit more you can get a room AC with a vent hose. The good ones discharge the condensation out of a vent hose, and can be semi-permanently installed. Just remove the hose from the hatch when you leave the dock. This is my preference for when an installed AC is not realistic.

    Note that the way most dehumidifiers work is to either 1) heat the air thus reducing relative humidity. Or 2) a condenser coil uses refrigerant to cool plates, which then causes condensation. This water then is collected and ejected from the environment.

    Note that option 2 is almost exacally what a AC does, except that is reintroduces the hot air from running the compressor back.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I don't think you need a dehumidifier, just a good, well fitted cover that keeps sweet water out of the boat and proper ventilation under it, say with a couple of Nicro's. Place one vent forward and the other aft, in the cover, with one blowing in, while the other is blowing out. This will set up a pass through draft and the boat will not get mold or mildew. Get the solar/nicad vents so they can run 24/7.

    If you have the choice, never let sweet water collect in the bilge or elsewhere on the boat. This is what rots wood. With proper ventilation and keeping the confined spaces in the boat (lockers, cabinets, bilge boards, etc.) open, air circulation will keep it safe and sound.

    Also hanging a few incandescent bulbs in key locations will thwart off condensation and the occasional drip. It'll also keep bilge water from freezing in the winter too.
     
  5. Mark Cat
    Joined: Jun 2011
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    Location: Michigan

    Mark Cat Senior Member

    I think PAR is correct.

    The reliable solution for what you describe is forced ventilation. I like powering the minimum ventilation blowers using a solar panel(s) system. This will keep the boat dry and the interior should track outside ambient. When you get on board then you can start up the Air Conditioning.

    The trend is to provide small forced ventilation continually, and control using a daylight sensor or timer, and then when on-board have the option to move to a higher speed setting. Just moving a lot of fresh air through a cabin has a cooling effect but at much lower energy than AC.

    HVAC is really dependent on how well the space is insulated. If well insulated, HVAC equipment can be very small and energy efficient.

    One application for dehumidifiers is to address high latitude vessel interior condensation in cold weather.

    Mark
     
  6. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    Around this part of the world, ambient humidity is frequently around 100%. Even now on what passes for a hot sunny day (65 F) the humidity is 54% and this will increase substantially when the sun goes down.
     
  7. Mark Cat
    Joined: Jun 2011
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    Location: Michigan

    Mark Cat Senior Member

    cthippo,

    Is the problem condensation, where? or are you just uncomfortable?

    If this is an uninsulated aluminum boat I can see where moving air across a cold hull could substantially increase condensate. But, most of the boats I have been working on for the past 2 years are insulated using Mascoat, with the panels having additional insulation. So dry in the sense of no condensate. Not dry with a reduction in relative humidity for attaining a comfort level.

    So my guess is you will deal with the humidity using a cabin heater after the sun goes down tonight? and if no heater then a dehumidifier?

    How do you dry out your boat?

    Thanks,

    Mark
     
  8. 1956Holiday
    Joined: Jan 2011
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    Location: Prospect, KY

    1956Holiday Newbie

    Thanks for the replies

    Appreciate all the replies. I should have been more specific - other than saying it is a 20' Holiday. This is a runabout. No cabin, AC, etc.

    [​IMG]

    [​IMG]

    I am worried about rot with the heat and humidity.

    Appreciate it.
     
  9. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member

    In an open boat like this there just isn't much you can do do lower the humidity of the hull itself. Though a solar blower into the bilge can help keep humidity from condensing. I would suggest a boat cover however. At least herein New Orleans it can be so humid that rain won't evaporate, so a cover that keeps the rain off is great. When doing this though it is critical to have lots of ventilation under the cover.
     

  10. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Here in Florida we well know of humidity and heat. If the boat is the water, you're kidding yourself about controlling humidity. If the boat is on it's trailer you have some options. In both situations a cover and forced ventilation is the cure, simply put. It's well understood and well tested. Again, on your boat, a couple of Nicro's mounted in the cover, with everything possible opened up on the boat (lockers, stood up cushions etc.) will keep moisture vapor from lingering on any surface long enough to cause trouble. This the key, moisture vapor has to have time to condense and collect, before it can cause issues. If the air is moving, it can't; hence the problem eliminated or substantially mitigated, depending on how long she's forced to live under cover.
     
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