Question about completely foam filled hulls

Discussion in 'Boatbuilding' started by Jmooredesigns, Dec 25, 2016.

  1. TANSL
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    TANSL Senior Member

    upchurchmr:
    You make me feel like I've said or done something wrong and I think this is not so. Anyway, just in case, I apologize also to everyone, although I do not know why.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Not really. Only if it (foam) gets preferentially placed along the centreline, and water can enter voids away from the centreline, then you certainly are increasing the chances of a capsize. If the whole undersole area is foam packed, the boat has very similar stability characteristics to the same boat, intact and sealed underfoot, with no foam.
     
  3. ondarvr
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    ondarvr Senior Member

    Boats under 20' in the US are required to float upright and level now, back when Whaler started their marketing program that wasn't a requirement. Whatever method of floation is used the boat needs to be able to still float if the chamber is ruptured. Foam has issues, but is a low cost and rapid way to meet the requirement.
     
  4. JamesG123
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    JamesG123 Junior Member

    In sandwich skin composite construction, the foam does not actually take any loads, it simply passes them to the skins. The same way that all the stresses on a bolt or shaft are concentrated on its surface. This is why very good aeroplanes (and boats) can be built of foam with thin skins of fiberglass that would be as flimsy as an empty plastic bottle without it.
     
  5. TANSL
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    TANSL Senior Member

    I think we should clarify some concepts. The foam does not transmit any load to the outer layers of the sandwich. What it should do, fundamentally, is to withstand the shear stresses that occur between the various layers. These shear stresses as well as stresses/compressions are due to the loads applied to the structure. The foam must also absorb tensile or compressive stress, but of very low level. That is why it is always placed in the core and not on the outside of the sandwich. It does not have the capacity to absorb great tension/compression loads.
    The other issue, that all the efforts on a screw are concentrated on its surface, does not seem right either. In bolted or riveted constructions, the screws or rivets mainly support shear forces. If the subject were as you say, it would not make sense, in some cases, to place these solid elements, they could be hollow.
    I hope my poor English has been enough to explain what I think.
     
  6. JamesG123
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    JamesG123 Junior Member

    No offense but your English is better than your understanding of engineering. I suggest you read a few composites books.
     
  7. TANSL
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    TANSL Senior Member

    Thank you, my friend, I will follow your advice. You could also study a little more about resistance of materials and theory of elasticity that is the same even for composite materials.
     
  8. upchurchmr
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    upchurchmr Senior Member

    I think the English is the problem.
    One little word with a slightly different assumed meaning makes it seem there is a lack of understanding.
     
  9. Barry
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    Barry Senior Member

    1) The foam will be under tension and shear stresses and perhaps others. It cannot be under no load as you suggest, and yet transfer loads to the skins.

    2) your comments that all the stresses on a bolt or shaft are concentrated on the surfaces are incorrect. Shear only and tensile only stresses are pretty much constant over the cross section unless there is are bending stresses which can create higher tensile stresses at the outer diameter than say toward the neutral axis

    Of course stress concentration can be quite high at the roots of the thread and if the bolts design criteria is to resist mainly tension, this stress concentration is often the most significant design parameter
     
  10. upchurchmr
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    upchurchmr Senior Member

    +1 I see we have an Engineer
     
  11. TANSL
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    TANSL Senior Member

    You are quite right. I assure you that it is not easy to discuss technical matters when a language is not mastered but, in my opinion, it is preferable to try it, than to remain silent. I believe it will always be possible for a reader with technical and language skills to separate syntactic errors from conceptual errors. At least, I hope so.
    Thank you all for your patience with non-English speakers.
     
  12. JamesG123
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    JamesG123 Junior Member

    Yes... the only people who can miss the point of a comment in the pursuit of pedantic perfection.
     
  13. SamSam
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    SamSam Senior Member

    Attention to detail comes in handy when building boats and airplanes. Correcting these incorrect statements doesn't seem to be pedantic perfection to me.
     
  14. TANSL
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    TANSL Senior Member

    JamesG123 : But my friend, making mistakes is not so serious. We all make mistakes. What is serious is not being able to recognize it.
    We all have to keep studying, do not despair.
     

  15. upchurchmr
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    upchurchmr Senior Member

    I beg to disagree - most people I know miss the actual point of a discussion, engineers are just really single minded about it. :p

     
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