Strip plank construction in alternative materials

Discussion in 'Sailboats' started by Ivanthefool, May 11, 2017.

  1. mojounwin
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    mojounwin Junior Member

    I'm in the process of building a boat with foam strips. One side of the foam is glassed with unidirectional glass and cut in to strips
     
  2. TANSL
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    TANSL Senior Member

    mojounwin, have you taken into account that foam, as a resistant element, is very ineffective ?. That, along with the unidirectional glass, will produce a poorly resistant hull. . The toughest of all that set is going to be the glue used to attach the strips.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Tansl,

    Perhaps you ought to ask what kind of foam.
    If it's polystyrene I'll agree, but there are others which are used in some very good construction.

    I can't figure why anyone would use unidirectional glass though.
     
  4. TANSL
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    TANSL Senior Member

    upchurchmr,
    You're probably right. I recognize my ignorance by not knowing any foam that can be used as a resistive element, even though they may be used in construction. I thank in advance who can get me out of my ignorance.
     
  5. mojounwin
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    mojounwin Junior Member

    I'm not familiar with the term, "resistant element" resistant to shear? Impact resistance??

    The Uni glass is to add longitudinal stiffness as would the grain of a timber strip. Helps the foam strip keep a linear curve during the build process.

    Once the foam is layed up it is covered with Double bias glass each side.

    The foam is just a core, not an independent structual element.
     
  6. TANSL
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    TANSL Senior Member

    Well, things are getting better now. I thought you were just going to put unidirectional glass (how many layers?) On the outside.
    You could use the foam as if it were a male mold that will serve to shape the glass. In that case, once the glass has been molded and cured, the foam can be removed.
     
  7. upchurchmr
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    upchurchmr Senior Member

    Tansl,

    I also don't really know what you mean by "resistive element".
    The polyurethane foam for boat building certainly "resists" shear, since that's what it's there for.

    Do you have some special meaning for "resistive element" that we don't know?

    I know we sometimes have an English problem, so please help me.

    It was not a part of my engineering structures education.
     
  8. TANSL
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    TANSL Senior Member

    upchurchmr,
    I'm not very good with English but if you put a little of your will, I'm sure you'll be able to understand what I mean. By "resistive element" I meant an element that is able to withstand the stresses to which the hull and internal structure of a ship are exposed. Stresses that are not only shear but also of other types (as you know perfectly thanks to your "engineering structures education").
    If I have not explained well, let me know and I will try to do better. But I do not have the slightest doubt that your technical knowledge and my interest in improving with English will get you and me to understand each other. Best regards
     
  9. upchurchmr
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    upchurchmr Senior Member

    Tansl,

    We always work on the English meaning.

    In this case I just think you neglected the shear function for foam core as a resistive element.

    Because as I said, if we are talking about polystyrene foam I agree it is not a resistive element - not enough stiffness to be effective. More like an elastomer.

    Let me know if you disagree about polyurethane foam intended for boat building core.
     
  10. mojounwin
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    mojounwin Junior Member

    The foam is Gurit H80 polyurethane.
    Polystyrene isn't a foam I'd use to build a boat with.

    The foam is being used as a core not a mould. Having a solid glass hull would end up far heavier and waste the expense of the foam.
     
  11. TANSL
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    TANSL Senior Member

    Of course I agree. Foam is probably one of the worst solutions to be used as a core but it can effectively withstand the shear stresses. It would, however, be advisable to check that it can withstand those produced in that boat, with the planned laminate schedule.
    I agree, too. I wonder where, at what point in the structure of a ship, the use of foam is profitable. So my advice to the OP is to discard the idea of using foam.
    Do you see how, despite my bad English, if you try, you can understand me? Thank you.
     
  12. upchurchmr
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    upchurchmr Senior Member

    Tansl,

    We can agree when you finally state what you mean. The English is just an extra problem we have to work around. I have a problem when you make a statement that is not true. Its not my problem with your English - we can always get that understood.
    Polyurethane foam has been used for core for at least 30 years on lots of boats.
    I don't understand your statement that it is the "worst" solution.
    It is quite structurally efficient when used properly.
     
  13. TANSL
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    TANSL Senior Member

    Even for a poor English speaking, saying that foam is one of the worst solutions is not the same as saying that it is the worst. Please read again what I have written.
    Although the language is indeed my problem, I prefer to try to communicate myself to be silent in a discussion that interests me and to which, I humbly believe, I can contribute things.
    It depends on what you mean by "structurally efficient" because in some case maybe I do not agree with you. Use your knowledge and experience as an engineer and try to find out if the foam, even if properly used, is in any circumstance "structurally efficient". I do not think so.
    Anyway I prefer to talk about effective rather than efficient.
    Note:
    - efficient, who does things well.
    - effective, which does well what needs to be done.
     
  14. upchurchmr
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    upchurchmr Senior Member

    Now your creative English is the problem. Efficient - contributes to a structural solution which is weight optimised.
    Note that I also did not say the absolute best.

    As in: A solid laminate would be much heavier than a foam sandwich, which was pointed out by the OP. Both can be structurally effective - which actually means they both can succeed at doing the job.

    Enough hijacking the thread. I'm done.
     

  15. TANSL
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    TANSL Senior Member

    upchurchmr,
    This thread, from post # 16 has run through other paths other than the OP. I have tried to give to mojounwin reasons why, in my opinion,he should not use the foam in the way he had planned. I do not think, honestly, that this is to hijack the thread. But I will not continue to argue with someone who prefers to criticize my English rather than explain for technical reasons why I am not right. A warm greeting to you, engineer.
    End of my speech in this interesting technical ;) discussion ....
     
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