Tortured composite panels?

Discussion in 'Fiberglass and Composite Boat Building' started by Robert Biegler, May 7, 2021.

  1. Robert Biegler
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    Robert Biegler Junior Member

    I am not planning to build a boat, I am just curious about the following: would it make sense to make composite panels with foam and a layer of laminate only on one side, then use the tortured ply method, laminating the insides only once the hull is in the jig and bent into its final shape? Would that be faster than sandwich composite with either a mould or foam tacked onto stations?

    I have never heard of anyone using that method, so does it have flaws that I have missed? Apart from being restricted in the shapes you can build.
     
  2. TANSL
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    TANSL Senior Member

    I don't know if I have understood you correctly. If not, I beg your pardon. The method has been used but not as you propose it.
    There is no point in putting a core resistant to traction or compression, such as plywood, in the center of the laminate where the values of tension or compression are very low. The properties of the sandwich are not greatly improved but its weight is greatly increased.
    Plywood is used and, to seal it, one or two layers of fiber are placed. What is done now is, since the fiber is going to be laid, take into account that it will absorb part of the load and that, therefore, we will be able to reduce the thickness of the plywood.
     
  3. Robert Biegler
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    Robert Biegler Junior Member

    I was not thinking of using any plywood at all, only of applying the tortured ply method. I didn't know whether anyone would know what I meant if I called it only a tortured panel. The idea is to make panels out of foam and laminate only on the outside, so that it is still easy to bend. Then bend the panels into shape in the jig, just like a tortured ply hull, and only then laminate the inside. You'd get a foam composite hull. The only mould needed would be a flat laminating table. The hull should be as fair as the table, without further sanding and fairing. How would that compare to other methods of building a foam composite hull?
     
  4. TANSL
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    TANSL Senior Member

    Sorry I thought the tortured ply method you were talking about was only applicable to boards (plywood or any one). If you refer to shaping strips of wood, metal or HDPE panels, wooden planks, ... that is our daily bread and butter in shipbuilding. If you refer to bending panels (plywood or not) part of what I have told you is still valid.
    Excuse me, then, for not understanding you.
     
  5. Robert Biegler
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    Robert Biegler Junior Member

  6. TANSL
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    TANSL Senior Member

    But that's what everyone does, I think, with total normality.
     
  7. Robert Biegler
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    Robert Biegler Junior Member

    I didn't find a a single example when I searched. Would you have a link, or a suggestion for a suitable search term?
     
  8. TANSL
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    TANSL Senior Member

    Just google "boat sandwich construction"

     

    Attached Files:

  9. Robert Biegler
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    Robert Biegler Junior Member

    1) a.b.b. - amateur boat building - How to build a foam sandwich composite boat https://amateurboatbuilding.com/articles/howto/foam_sandwich/index.html
    What is described here is not what I am asking about: "We will create a foam hull shape around a wooden jig, fiberglass the outside, flip the hull, remove the jig and fiberglass the inside skin." The only thing that has in common with what I am asking about is that the outside is laminated first. It is not a flat panel bent into a jig, which is the bit I care about.

    Then, because that search term gave me a lot of stuff that had nothing to do with what I want to know, I switched to picture search. Not a single one that I found showed what I am interested in. Here are examples:
    https://curveworks.nl/wp-content/uploads/2016/03/foam-cores.jpg
    http://www.yachtdesign.com.br/img/ex39/3f270f12.gif
    https://www.glen-l.com/methods/mthdfg08.jpg
    https://uk-cherub.org/lib/exe/fetch.php/boats/2675-1999xxxxa.jpg

    If these pictures show what you have in mind, then we are not discussing the same thing. For what I am interested in, the picture in post #5 of this thread is fundamentally different from those in this post. The same goes for the pdf you supplied.

    In the pdf and the pictures I found, the method is
    1) Build something that looks like the hull, with stations and stringers
    2) Attach the foam so that it takes on the shape of a hull
    3) Laminate the outside (assuming a male mould or jig)
    4) Take the hull off the jig or mold, laminate the inside.
    You get the shape before you laminate.

    What I am asking about is:
    1) Make flat laminating table
    2) Put fabric on the table, cut to size, wet out with resin
    3) Put foam on the fabric, vacuum bag.
    4) Cut to approriate outline
    5) Repeat with other panel
    6) Join along the keel
    7) Bend into the deck jig. There is no jig that is shaped like the hull.
    8) Laminate the inside
    You get the shape after you laminate the outer skin. Totally different procedure, not what is in the pdf.
     
  10. wet feet
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    wet feet Senior Member

    I understand the concept and have never known it to be done.With most,probably all,composite panels you would find it difficult to deviate very much from a hull surface consisting of linked conic sections and then you would have quite a lot of difficulty fairing the chine bonding strips.To create a hull that is constrained in such a manner would very likely mean acceptance of a number of compromises,so how far would you go to make a compromised boat just to satisfy your curiosity?
     
  11. fallguy
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    fallguy Senior Member

    Yes. I am doing it on a dinghy plan in the future.

    The designer will remain unnamed at the moment.

    He has advised doing one side and I want to do the other side first. I want the inside table laminated, then torture, then glue up, then seam up the inside, flip the boat and laminate the outside in a single or seams and a single.

    afa speed, it should be a tad faster if we can reduce outside fairing, but that is the only way to make it faster and it all the panels are done under vac, not much gained...I think it we table laminate 6oz no vac, we can work pretty quickly and then perhaps we'll bag the outside in a single go

    the whole goal is to reduce in the bag events on limited table space
     
  12. TANSL
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    TANSL Senior Member

    @Robert Biegler, I beg your pardon for wasting your time with such nonsense.
    In shipbuilding it is difficult to invent anything. What is not used is, normally, because it does not work. It has been tested but is not interesting or the current tools at our disposal do not allow it.
    Good luck with your experiment.
     
  13. Robert Biegler
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    Robert Biegler Junior Member

    Then we're getting closer. I wonder why not. I assume there is a good reason.

    True, but possibly less so than for plywood. Say I wanted to build a 1980s style A-cat hull designed for tortured ply, but I wanted foam composite. I would know that the hull shape is possible with plywood. If I made a fibre and resin outer skin with half the stiffness of the plywood, and added the conventional thickness of foam, I doubt the outer skin and foam panel would be as stiff as the plywood in the original plan. So I should have an easier time bending the panel into shape, and more freedom to deviate from conical sections. Then laminating the inner skin, again to half the stiffness of the plywood in the original plan, but separated from the outer skin by foam, should give me a hull skin more resistant to slamming loads and to buckling failure than the original plywood. With those scantlings, I might also have more weight, but for the moment, I am only concerned with whether a hull can be built that way.

    Bonding to already hardened resin might be more difficult than bonding to dry plywood. So there might be a problem. I don't know enough about the strength of secondary bonds. I thought increasing the bonding area would take care of that.

    Similar as when using plywood, I think.

    I wouldn't. I am just curious why this method is not being used. It would seem to be less work than building a hull-shaped jig, laminating the outside, then the inside, then fairing. And I am pretty sure it would be less work than building a female mould.

    Perhaps the answer is as easy as good plywood having been cheaper than composite when the hull shapes that can be achieved with that method were considered acceptable, and now that good plywood is relatively more expensive, most designers want hull shapes that can't be achieved with that method?
     
  14. Robert Biegler
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    Robert Biegler Junior Member

    I hope you'll be willing to report on how it goes.

    What advantage do you expect from doing the inside first?
     

  15. Robert Biegler
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    Robert Biegler Junior Member

    I should have started with the picture I put in post #5, instead of assuming that everyone would make sense of my description of a method popular from about the 60s to perhaps the 90s. Sorry about that.
     
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