Layup schedule help

Discussion in 'Fiberglass and Composite Boat Building' started by Scuff, Sep 5, 2017.

  1. TANSL
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    TANSL Senior Member

    I'd need layup schedules you want to compare, dimensions of the panel to be calculated as well as general data :
    Design category
    Power or Sail
    Length of the Hull (LH) m
    Length of the fully loaded waterline at mLDC m
    Beam of the hull (BH) m
    Beam of the fully loaded waterline at mLDC m
    Depth (Dmax) m
    Draugth at mLDC (TC) m
    Loaded displacement mass of the craft (mLDC) kg​
     
  2. gonzo
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    gonzo Senior Member

    The thickness affects stiffness by a power of 3. Therefore, keeping the total thickness is the most important thing. If you calculated the strength of the lamination by itself and it is equal to the original but thinner, you can increase the core thickness and the stiffness won't change. However, since you are using epoxy which has a larger modulus of elasticity, the properties of the laminates are different.
     
  3. TANSL
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    TANSL Senior Member

    I do not want to argue about this, nor do I say that it is not true, but I would like to see some formula or some technical reason that supports this claim. How do you measure or define stiffness?. In any case, rigidity is not the most important parameter to achieve. In general it is that the tensile or compressive strength to which the material is subjected, throughout its thickness, does not exceed maximum admissible values.
    No, that's not right. The same strength can be achieved, or at least a sufficient strength, with different thicknesses.
    I agree with that. Whenever different materials are used, the properties are different.
     
  4. fallguy
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    fallguy Senior Member

    It would be good for some resolution because if I, for example, build a solid frp laminate with four layers of 22 oz or I build a single sandwich with Corecell M and one layer of same glass each side; I'd like to think the comparisons are scientific. And I am not hijacking, but making a point that this is a little confusing is all. Thanks.
     
  5. TANSL
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    TANSL Senior Member

    @fallguy you are very right. It is easy to say things without a technical basis and without being willing to demonstrate them convincingly. The regulations of the Classification Societies have formulas that allow you to make the comparisons that you request. The ISO 12215 standard also has the formulas for the scantling of small boats (less than 24 m). With all of them you can calculate and compare different schedules of laminates.
    I will try to study what you propose and I will tell you if I have achieved something that clarifies our ideas.
    And you are not hijacking the thread. Your question is totally relevant.
     
  6. TANSL
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    TANSL Senior Member

    See attached a file with the comparative study of two laminates of exactly the same thickness :
    • 1st laminate, Solid: 4 multidirectional fabrics of 600 gr / m2 (MD 600)
    • 2nd laminate, Sandwich: 1 MD 600 + Coremat XM2 (1.48 mm) + 1 MD 600
    As can be seen in the results, while solid laminnate seems to comply with the minimum requirements, the sandwich laminate does not meet several requirements.
    At your disposal for all you want to comment. Gonzo's experiences would also be enlightening.
    As a complementary study it would be necessary (really it is compulsory) to calculate the distribution of the stresses in the thickness of each laminate to verify that not only the minimum required thickness is met, but in none of the layers the maximum admissible stress is exceeded.
     

    Attached Files:

    Last edited: Dec 7, 2017
  7. fallguy
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    fallguy Senior Member

    I would comment the weight of the sandwich panel is half. That may sufficiently anger gonzo, who I respect. But thickness is not the endall as you could increase the core thickness lots; perhaps impractically, to achieve more stiffness?
     
  8. gonzo
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    gonzo Senior Member

    I am referring to increasing the thickness by the same amount as a layer of mat.
     
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  9. fallguy
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    fallguy Senior Member

    So a better compare would be the same sandwich with the same layup with and without the mat as per the op. Got it-that would be good to see the impact of 1708 with vs w/o mat.

    I'd like to know if mat tapes are stronger, too, versus non, but a hijack.
     
  10. TANSL
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    TANSL Senior Member

    I'm not sure what you mean when you talk about "stiffness". If they refer to tensile / compression resistance, I have to clarify that the core does not contribute anything to this. The core only has to withstand the shear stresses that occur between the various layers.
     
  11. TANSL
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    TANSL Senior Member

    Could you propose exactly what you want to compare?
    Sorry, mat tapes stronger than ... what?
    Keep in mind that the fact that something is stronger than something else is not very important. The important thing is that both are strong enough. Achieved that, you can opt for the combination of lower weight, or that involves less labor, or the one supposing a lower consumption / price of materials.
     
  12. Scuff
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    Scuff Junior Member

    Gonzo, I believe you are saying the stiffness of the laminate itself not the sandwich as a whole? Does using epoxy improve the laminate when compared to poly or vinyl? By improve I mean the stiffness my understanding is it's better in elongation.
     
    Last edited: Dec 8, 2017
  13. TANSL
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    TANSL Senior Member

    In case it helps you to clarify things, in the calculations that ISO 12215-5 stipulates that must be done for small boats, the strength provided by the resin is not taken into account. It does not mean that the resin does not contribute, but it is necessary to verify that the strength of the fiber, by it self, is adequate.
     
  14. Scuff
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    Scuff Junior Member

    For a multihull which beam numbers do you need?
     

  15. TANSL
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    TANSL Senior Member

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