extreme shrink-swell stabilization

Discussion in 'Wooden Boat Building and Restoration' started by braddimock, Jul 21, 2007.

  1. braddimock
    Joined: Jul 2007
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    Location: Northern Arizona

    braddimock New Member

    Hi-
    In 2002 I built a replica of a 1937 lapstrake whitewater boat. It is 15' long with a 7/8" thick plank floor (tight butt-jointed together, screwed to the ribs.) I ran this boat on a variety of rivers, logging about 3000 miles with marvelous ressults
    (see http://www.fretwater.com/dimock.html and http://www.fretwater.com/dimock2.html for pictures of the construction and operation of the Julius).

    The problem, which becam increasingly severe with each trip, is the extreme swelling of the bottom planks each soaking (about 1.5" on a 50" bottom), followed by extreme shrinking as I hauled it across the desert to the next trip. The cracks are now so wide it will no longer swell shut. I need to do something.

    My thought is to pull the planks of and soak them in something that will permanantly swell them to "wet" width and harden like that. Then re-affix them to the boat.

    Is there such a product? I have heard of PEG that wood-turners use for lathe projects. Also a combination of acetone and varnish.

    Any great ideas? It is such a pretty boat and I do want to get it back in a stable usable condition.

    Thanks!

    Brad Dimock
     
  2. Otterisland
    Joined: Jul 2007
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    Location: Italy

    Otterisland Otterisland

    It looks like you had an enviable time with your small boat. No advise, only envy from Otterisland. My best,
     
  3. KnottyBuoyz
    Joined: Jul 2006
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    Location: Iroquois, Ontario

    KnottyBuoyz Provocateur & Raconteur

    I don't think PEG will work with your boat Brad. Just looked it up on Wikipedia because I've seen my brother use it in furniture restoration and it appears it's water soluable. :-( My brother has used it to tighten pintles and spindles that have shrunk on old rocking chairs etc. and it worked to stabilize the wood. He first treated the ends with glycerine though which swells the ends. Not sure exactly what part the PEG plays in the whole process.

    I don't know how to fix your planking problem but will keep an eye out for any hints tips or tricks.

    Good luck.
     
  4. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    It wasn't the drying that did it, it was the swelling. Wood almost always comes back, but when swelled hard, it is sometimes crushed from caulking when too dry too tight---- some woods such as cedar are not so prone to this problem.
    One tried and true way to fix the planking is to skil-saw out a clean kerf (gotta wait til it's dry to do this) and then glue in narrow strips. The strips are epoxied to one side only. The other side should be protected from adhering (wax paper and a thin spacer that you can tug on (aluminum flashing) on the no-glue side of the wax paper.
    PAR may have something to say about this too, when he catches the thread. Right up his alley.

    Alan
     
  5. braddimock
    Joined: Jul 2007
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    Location: Northern Arizona

    braddimock New Member

    I think the idea of sawing out the kerf and filling it with new wood would work if I didn't plan on more desert boating. But as long as I live in a zero-humidity area and wish to use that boat, I fear I have to find a way to minimumize the amount of shrink-swell, or it will just tear itself to bits again.
    I am all ears. Thanks for the ideas so far-

    Brad
     
  6. alan white
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    Location: maine

    alan white Senior Member

    There may be nothing you can do, however. Nothing I've ever heard of is going to control the wood except limiting the degree it can dry out. Short of an artificial humidified storage environment, that is.

    Alan
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The carvel planking on the bottom (my assumption) was pounded tight with one or a combination of things going on, which are: the moisture content of the lumber was relatively high when caulked, the seams were caulked too tight, the species used was particularly dense or you used a flat sawn lumber.

    Any one of these things or a combination (likely) will cause your woos. Without more details it would be a guess as to a procedure to continue.

    Options include refastening, recaulking, planking replacement on the bottom and 'glassing the bottom up to the lower strake. Removing the bottom and refastening (probably with a "stealer" or filler strip to make up the difference) would be reasonably easy. Recaulking could be easier, but the seams widths need to be reasonable. 'Glassing the bottom could be a solution, but can also open up a whole new can of worms for you to chew on. If you used flat sawn lumber or particularly dense material, the moisture gain/lose is so great that you'll have difficulty keeping the seams closed. The only solution to this is replacement of the flat grain planking.
     
  8. braddimock
    Joined: Jul 2007
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    Location: Northern Arizona

    braddimock New Member

    Thanks PAR,

    I think you are right. Although when we built the boat, the wood was quite dry and butt-jointed tight without caulk, I fear it is flat-grain and not vertical grain. That being the case, perhaps there is no recourse except to replace the bottom. I as much as it is a repilca of an historic craft I really don't want to do any fiberglassing on it--I'd love to do what I can within the parameters of the original building method.
     

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

    PAR Yacht Designer/Builder

    Flat sawn lumber will move a lot through wet/dry cycles. Typically, planking stock on traditionally constructed craft is the finest wood on the boat, for obvious reasons. Vertical grain lumber usually needs to be custom ordered. The only thing vertical in the lumber department of the local home remodeling center are the prices.
     
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