A Hull Sheathing Alternative?

Discussion in 'Wooden Boat Building and Restoration' started by Wayne Grabow, Nov 14, 2010.

  1. PAR
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    PAR Yacht Designer/Builder

    I have to admit it's splitting hairs a bit, diagonal planking, cold molding, though I have issue with calling anything as thin as 6 mm a plank, unless it's on a skiff.

    I'm not sure where the distinction delineates, but diagonal planking has been around for a few hundred years folks. I'm a big fan of double diagonal planking and of Ashcroft, which is also diagonally molded planking.

    I would guess the distinction would permit one of the planking techniques to tolerate some edge set. Naturally, you'd want to avoid this in a molded hull, as the veneer will cup or otherwise not lay flat against the mold, but in real planking you can get away with some edge set, particularly as you twist it into position.
     
  2. goodwilltoall
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    goodwilltoall Senior Member

    Greetings,

    What would be the maximum thickness allowed for strips of say 3" wide pine before the internal stresses would become to great? Would you be able to go upto 1" thick? Whats the limit? Reason for asking: if you needed a 2" thick hull would the first longitudinal layer be able to be 3/4" T&G rather than ply, then the sucessive 2 or 3 smaller layers added on top.
     
  3. PAR
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    PAR Yacht Designer/Builder

    A lot would depend on the hull shape. Ideally, you want really thin laminations, much like plywood. If you need a 2" thick hull then it's probable the design isn't considering all the possible planking options or you're working on a very large design, at which point wood becomes a core for the most part. 3/4" tongue and groove hasn't any place in a reliable laminate for the most part. I've seen it done, but you're stretching what can be done with epoxy glue lines and it serves no benefit to have 4 - 1/8" veneers then a 3/4" plank glued over it. In other words if you're molding a hull, then you have to accept the need for thin lamination layers, if for no other reason then to orient the wood fibers where you need them.
     
  4. Wayne Grabow
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    Wayne Grabow Senior Member

    Thank you for the many and varied replies. It is nice to be able to compare viewpoints. I have been considering 4-6 mm. layers which apparently set off a minor controversy as to whether these are veneers or planks; I wasn't sure which name to use myself.

    The boat size I am considering would be 18.5' by 6', a fairly small size. On the last hull I put on a layer of plywood and a layer of planking/veneer. Yes, the plywood went quicker but neither was too difficult, and I had better control with the planking. Waste-wise, plywood comes in 4' widths and once you cut out a 2' or 3' wide, curved sheathing panel, the remaining 1-2' is pretty much scrap. With 3" wide planks laid side by side, you only lose a little waste at the ends (plus re-sawing). The hull uses 14 frames (incl. transom) so the sheathing is well supported. I want the bottom to be thicker than the sides. Being able to re-saw planks to desired thicknesses and use multiple layers provides added flexibility.

    At least it has been established by your knowledgeable replies that multiple layers of 4-6 mm. is a valid option and can be considered in my future decisions.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Waste also includes what goes with the saw kerf as you mill it down to 4 mm. This is likely 40% of a 4 mm plank and not an unsubstantial figure. Unless you're finishing bright, in which case the thinnest veneer is all that is necessary, thinly milled solid stock doesn't offer much to a developed surface.
     
  6. michael pierzga
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    michael pierzga Senior Member

    Gee wayne...many solutions and many different ways to build a boat !!.. sounds like you have a pretty good understanding of what you propose. .sometimes its best to supply a sketch of a proposed project. Some techniques are more suitable to different shapes and uses. Oh, and good luck with your project !!
     
  7. Landlubber
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    Landlubber Senior Member

    hey Wayne, have a gander at strip planking too, in an 18 footer it is a good way to get shape if that is the design you like. Epoxy glued and coved, the strips become one great bond together, they are easy to fair and very pretty if done bright.....just another idea.
     
  8. gonzo
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    gonzo Senior Member

    Michael; you are posting nonsense. Plywood is timber. It will add several layers to the final laminate.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Plywood is a wood product, not timber, though it is made from timber. Plywood is the "Cheese Wizz" of the lumber industry.
     
  10. goodwilltoall
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    goodwilltoall Senior Member

    Wondering whats the difference between coldmolding and diagonal planking?

    Could the 3/4" (plank) serve as the first layer and the succesive smaller layers go ontop?

    Also heard of appling epoxy and fabric to both sides. Why is the interior necessary?
     
  11. apex1

    apex1 Guest

    If you would ever read a thread before you ask or drivel, you would find the answers easily.:mad:
     
  12. Wayne Grabow
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    Wayne Grabow Senior Member

    "Plywood is the "Cheese Wizz" of the lumber industry."

    Which is another reason to look for other alternatives for sheathing a hull. How would you like it if some one said, 'Oh, I see that your hull is covered with cheese wizz." Probably not as bad as frozen snot, but certainly the mark of the uninitiated and disrespected.
     
  13. PAR
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    PAR Yacht Designer/Builder

    The term I used above was to suggest it's a manufactured product, not a naturally occurring one, much like Cheese Wizz. This isn't to say it's not a good sheathing material, as the last 60 years of building have proven this quite well, not just in the boat building communities, but many industries have been hugely affected bu the advent of plywood and wooden sheet goods. In other words the term was used lovingly.
     
  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    One or two posts in this thread are being a bit unfair on plywood. It's an engineered wood product, made under controlled conditions to strict standards.The good stuff that is, not the crap that goes under house floors. In a cold-molded hull, are you going to get guaranteed 100% glue adhesion in a multi-layer skin assembled strip-by-strip over a humongeous and complicated 3-dimensionally curved mold in uncontrolled temperature and without bonding pressure and heat? I doubt it!

    Solid wood has 90% of its strength in one direction and diddly squat in the other. Ply has whatever strength distribution it is designed to have, usually but not necessarily close to equal. When you lay up wood veneers you may get something approximating plywood if you are lucky, but probably not as good.

    So go ahead and use strips of plywood in your cold-molded hull, Brynzeel if you can still find the real thing and can afford it, Lloyds if not, or BS1088 from a supplier with a rep at least. It will behave better and be easier to use than solid wood, uniform thickness, no checking etc.
     
    Last edited: Nov 19, 2010

  15. Wayne Grabow
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    Wayne Grabow Senior Member

    "In other words the term was used lovingly."

    And, in my case, the term "cheese wizz" was used humorously. I fully respect the properties of plywood but merely want to consider other alternatives as well for specific applications.

    Again, thank you for your advice.
     
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