Stringer material

Discussion in 'Boat Design' started by Ok J, Apr 23, 2005.

  1. Ok J
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    Ok J Ok J

    G'day
    I am currently overhauling a 18 ft 79' Fiberform. I am rebuilding the transom and stringers, my question is, can you use any other material for the stringers other than Douglas fir? I have come across Hem-Fir, and the Douglas fir I have found ( 2 and better ) is junk, and the clear Doug fir is hugely expensive ($11.00 per board ft Canadian). Are there alternative woods that will accept the polyester resin?

    Any help is appreciated.
    -Jeff
     
  2. gonzo
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    gonzo Senior Member

    Plywood and spruce will work.
     
  3. nero
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    nero Senior Member

    polyester resin with wood? Kinda thought this was not acceptable. Some pro could explain the problems with this combination.

    regards.
     
  4. Ok J
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    Ok J Ok J

    I believe I will go with epoxy after snoopin' around, especially after removing my old stringers from the hull today...in one piece. Slipped right out. Yikes!
    Epoxy it is.
     
  5. cyclops
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    cyclops Senior Member

    You can build the transom and the stringer out of only Marine AA or AC. Where the stringer meets the transom put a 6" x 6" piece of triangular stock on each side of the stringer. Epoxy up scraps of FRESH planed 2X6 pieces, cut to fit all 4 of the corners.
     
  6. gonzo
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    gonzo Senior Member

    Polyester over wood works fine. The problem is when water gets under the laminate. Any screw or hole has to be either caulked or sealed. Most boats are polyester over wood and get a reasonable life.
     
  7. chandler
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    chandler Senior Member

    Hemlock should be left to grow old and tall. Then used to build exposed porch roofs and posts as quickly as possible before it dries...
     
  8. Cary
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    Cary Junior Member

    Klegicel (spelled someway) a closed-cell high-strength rigid foam with a good epoxy resin and fiberglas cloth is pretty good
     
  9. Ok J
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    Ok J Ok J

    Transom meets stringer

    As I am laminating the transom today, and I have thought about how to properly tie in the stringers to the transom, what about notching the transom to recieve the stringers? (thru 1 ply at least?)

    Thanks for all the help...Ok J
     
  10. marshmat
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    marshmat Senior Member

    Notching one ply of the transom could be done; not quite sure how big an advantage it would be though.
    About the resin-wood thing: My own boat is built using polyester resins and plywood core, and is plenty strong. Where you get trouble is laminating over regular lumber. THe oils in the wood will prevent the bond form setting properly and the bond will delaminate. THis is not a problem with plywood as the manufacturing process takes these oils out.
    When attaching your stringers, keep in mind the possible ways they could fail. There are 4 main types of loading that will cause failure: compression, tension, sheer and peel. Adhesives and laminating resins will fail under peel long before the other factors come into play. When laying up your stringer grid, try to visualize the forces that it will take and try to avoid peel loading on the laminates.
    Is your stringer grid completely encapsulated? If so, the wood will act as a core, providing stiffness, while the surrounding glass will provide the strength. The quality of the bond between the two is critical! Any gap or weak spot in the bond between the stringer and the surrounding glass will subject the glass to peel loading and the failure will spread. Yes, epoxies are FAR better for this than cheap resins.
     
  11. chandler
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    chandler Senior Member

    Sounds like alot of work to notch the transom around the stringers
     
  12. Chris Krumm
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    Chris Krumm Junior Member

    The out-of-print Gougeon Brothers on Wooden Boat Construction was the "bible of wood epoxy boat construction technique. STiill a very good construction guide. They mention attaching stringers to transoms( or eck carlins to sheer clamps) by mitering the ends of the stringer and fitting those into angled notches . A final layer or two of veneer (or a thin sheet of ply) can cover it up and make it all beautiful. It works well. Structural fillets around the stringer/transom joint disperse the loads and prevent stress risers.

    Use epoxy systems comprised for wood construction. You'll find resin systems that are less toxic than polyester, bond better to wood with better mechanical properties, can be mixed with various fillers to create structural and fairing putties. It cost more than polyester, but that cost is trivial compared to labor.
     
  13. chandler
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    chandler Senior Member

    Why not loft the transom from the drawings ,take the bevels,fit it, and attatch the plank ends to it. What do the stringers have to do with the mix??
     
  14. cyclops
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    cyclops Senior Member

    Is the meeting place of the transom and the 2 stringers out of sight when the boat is complete? If yes, Just put the gusset blocks in the 4 corners. Maximum support for that joint. You will have a epoxy joint of huge strength without layers of cloth. I would put 1 or 2 small cloths over the triangles if you intend to jump waves normally.
     

  15. gonzo
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    gonzo Senior Member

    Overbuilding may cause serious problems. The adding of gussetts and other reinforcements creates hard spots. There was nothing wrong with the original design. The Polyester and mat over ply lasted for 26 years. It failed from rot not structurally.
     
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