Discussion in 'Multihulls' started by rturbett, Oct 13, 2021.

  1. rturbett
    Joined: Aug 2005
    Posts: 173
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    Location: FINGER LAKES, NY

    rturbett Senior Member

    I have wooden decked fiberglass hulls. On the rebuild, I did not put any portholes in.
    The only expected ventilation occurs when I take off the 1 inch drain plug on each hull.

    Any thoughts or concerns? all the wood on the inside has at least a light coat of epoxy on it.

  2. Blueknarr
    Joined: Aug 2017
    Posts: 1,219
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    Location: Colorado

    Blueknarr Senior Member

    Add ventilation.
    Increase interior epoxy thickness.
    Water vapor is insidious it will penetrate a light cost of epoxy and start the rotting of your wood deck.
    fallguy likes this.
  3. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Desiccant materials are available to soak up moisture, how you get that in and retrieve it through 1 inch holes sounds like the problem
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Is this query in relation to the American Shark Cat in the photos on your profile?

    Did you start a thread on here about your re-build?

    I would agree with Blueknarr and Mr E above re the effects of moisture , which could cause problems further down the road for you.
  5. Steve Clark
    Joined: Jul 2004
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    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    The two gods of wood catamaran building Skip Banks and Terry Richards ( Patient Ladies IV & V) didn't put hatches in because they figured if the boats never leaked, there would be no water in the hulls. If there was no water in the hulls, there would be no water vapor.
    The boats didn't leak.
    All they had were little vent holes in the upper transom to equalize the pressure inside and outside the hull.
    One spring day, PLIV's bow blew open. Wasps had made a nest in the vent hole, as the boat got hot the internal air got bigger and had no where to go. The pressure identified the stem as the weakest link.
    I buy the argument that if the b0oat doesn't leak it doesn't need ventilation. But if it leaks it certainly does need hatches. I launch new boats hoping for no leaks, but often have to put hatches in.
  6. Russell Brown
    Joined: Jul 2012
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    Location: washington state

    Russell Brown Senior Member

    I'd agree with all of that, Steve. The thing to remember is that it's water vapor, not water that can penetrate epoxy. That's why decks go first. The condensation collects on the undersides of the decks. I think keeping the insides dry, but being able to drop desiccant packs through small waterproof ports can work. My old motorboat is based on very old plywood Tornado hulls. I've kept them going by keeping the insides bone dry.

  7. Bob Oram
    Joined: Jun 2009
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    Location: oz

    Bob Oram Junior Member

    Decks are probably the hardest working area of a boat if thought about.
    As Russell says, water vapour (from condensation) is a fact of life in any enclosed space.
    As decks work, (sailing stress's, foot traffic), the underside veneer of plywood suffers from creep fracture, ie the veneer seperates longitudinally.
    Over time, moisture can penetrate the veneer and if spoor exists then rot can be the outcome.
    I have been glassing the inside of plywood boats for over 20yrs, especially the undersides of decks.
    This serves two purposes.
    1. It seriously strengthens the deck which reduces flex and reduces the chance of creep fracture enormously.
    2. It also contributes to the stiffness of the whole boat.
    I have opened up sealed compartments years later to find them dry, fresh and sweet smelling.
    Obviously only use epoxy.
    Hope this is of use.
    Regards Bob
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