Plywood design and timber moisture problem

Discussion in 'Wooden Boat Building and Restoration' started by longfellow, Apr 14, 2010.

  1. longfellow
    Joined: Apr 2009
    Posts: 39
    Likes: 1, Points: 0, Legacy Rep: 17
    Location: upstate NY

    longfellow Junior Member

    The issue is too complex to adequately describe in the title so I apologize to those who clicked and found this is out of their realm.

    I am getting out the frame timbers for the Glenn L 14 and the oak is checking badly. Normally this is not an issue because my boats are typically solid timber construction, so I would simply apply my own recipe of oils which do a wonderful job of retarding moisture release and preventing checking. I can do this without worry of glue adhearing because there is no glue; timbers went together with bronze fasteners. Now however, I am building a plywood boat for the first time and materials such as linseed oil, turpentine, tar, wax and such have no place where you intend to eventually epoxy the timbers together as well as epoxying the floor and deck beams, clamps, keel, etc to those same timbers.
    So my question is how to get checking under control on semi-green timbers (this is all that I have available out here in the sticks and at a buck a bf all that I can afford even if there were a kiln somewhere nearby, so I am limited to making this project work with high moisture content timber.) if I can't apply any of the time-proven oils that we all use to partially stabilize solid timber. Can I coat the wood with the same epoxy that will eventually be used for the assembly work, to stabilize it? Will this be ok on partially dried oak? Another option is to completely switch over to bronze fasteners everywhere that I would have applied oil, which gets me back to a construction method that I am familiar with but one that was not intended for this design. I have no idea if the designed overall hull strength can only be achieved by strictly adhearing to the designed construction method (guing frame and backbone members). I couldn't even glue the plywood hull panels on because the keel rabbet would be one of the surfaces that I'd need to soak with linseed oil.
    Unfortunately, using kiln dried, stable timber, which would solve this whole mess, is not an option. My question comes down to how to get checking under control, keep wood surfaces clean so that epoxy will stick, when one must use semi-dried timber throughout.
    Thanks in advance all for your suggestions. If it weren't for the huge ($$$) order of marine plywood that I am headed out to pick up, I honestly feel like abandoning this whole project and going back to the Atkin, Alden, Schock, and Mower designs that have worked splendidly for so many years. Why did I ever have to leave my element??? Oh, do I miss the smell of steamed oak right now.
    P.S. This is not intended to be a bashing of Glenn-L designs. In fact the plans are absolutely th best and most complete that I have ever seen and very accurate, and I am including those from the above-mentioned gods of naval architecture. If I can, with your help, figure this out I honestly hope to build more Glenn-L designs. I am just venting out of frustration.
    Last edited: Apr 14, 2010
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
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    Location: maine

    alan white Senior Member

    Well, to begin with, you must know that you could have had dry wood if only you were patient and you'd waited a few months.
    Checking is what oak does, though any wood brought into the shop heat in early spring is going to dry first (dramatically) on the outside, hence the checking.
    My suggestion is to treat the oak as you used to with your formula and skin the frame with plywood, but back-coat the plywood prior to assembly with three coats of epoxy (then do the same to the exterior after assembly).
    You'll be screwing the plywood on, which you should have done in any case.
    Then of course tape seams and whatever other glass application you'd planned on.
    It would also make sense to adhere the plywood to the frame with a good polyurethane or polysulphide sealant. This will allow fasteners to move a bit as the frame expands/contracts without allowing water to get into the plywood core via the screw holes.
    This is likely a dry-sailed boat anyway?
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