replacing timber beams with FG

Discussion in 'Materials' started by raf pali, Oct 7, 2013.

  1. raf pali
    Joined: Mar 2012
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    raf pali Junior Member

    Hi all.
    I want to rebuild my Wharram catamaran beams with fiberglass pipes.
    the original beams, as per plane, are 5 meters//16' Long solid timber (Pine) poles, 140mm//5.1/2'' Diameter. My idea is to make them, fiberglassing around a PVC pipe 130mm DIA with unidirectional glass fiber and Polyester resin, all hand laid. The PVC pipe is then left in as a core.
    The question is: HOW THICK the fiberglass should be?
    Thank you.
    Cheers
     
  2. raf pali
    Joined: Mar 2012
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    raf pali Junior Member

    Ok, no reply. I can't blame you. I can calculate the thickness myself if only someone can tell me the compression and tension properties of both materials.
    I googled it and got lost in the usual conflict between standard and imperial measurements. Some gives it in PSI some in N some in Pa and some per second square. None of them are familiar to me, all I want is kilograms per square centimeter or kilograms per square millimeter. Can anyone come to the rescue please?
     
  3. El_Guero

    El_Guero Previous Member

    There is no simple answer.

    And I am tired.

    But, you need to give more data. What was the design 'strength' of the pine you are replacing? Was it one piece, or composite?

    Pictures will always help get more answers.

    wayne
     
  4. raf pali
    Joined: Mar 2012
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    raf pali Junior Member

    I have no idea of the design strength, it is exactly what I'm trying to work out. it is a natural round pole sold in australia as copper log, no lamination and clear from knots, 5 M long all one piece.
     
  5. bregalad
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    bregalad Senior Member

  6. rwatson
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    rwatson Senior Member

    What Wharram plan uses treated pine logs ????

    I have never seen those !
     
  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    raf pali, if the fiber layers are correct, it is probably sufficient if you get new beams with the same modulus (relative to both axes) than older.
     
  8. raf pali
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    raf pali Junior Member

    Tama moana is the boat in question
    Cheers
     
  9. raf pali
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    raf pali Junior Member

    Sorry I cannot understand what you mean
     
  10. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    This is a very helpful site and when there are no positive replies there is a reason.
    As El Guero said there is no simple answer.

    This is meant in a kindly way, I am not wanting to have a go at you.

    You seem to be only considering bending whereas cross beams also experience tension, compression, shear, torsion, buckling etc. and several can occur at the same time.
    In addition crushing where they meet the hull and under the mast should be considered.
    The right amount of stiffness is a factor.

    Is there anything more important on a catamaran than the cross beams?

    I am shocked to see the boat is 37' 9" / 11.5m.
    If this was a one man beach cat that would be one thing but to put other people's lives at risk when you do not understand a straight forward statement by TANSL is unwise to put it mildly.

    If you insist on pursuing this idea take bregalad's advice and contact Wharrams.
     
  11. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I mean : modulus = Inertia / distance to the neutral axis

    (Inertia : second momento of the area)
    This is only a first approximation to the problem. Of course, the attachment of the beams with hulls is very important.
     
  12. El_Guero

    El_Guero Previous Member

    Here is an underneath look at your crossbeams.

    I think you would be better served by taking a replacement beam and having it wrapped in carbon fiber and kevlar.

    You have a lot of stresses on these crossbeams. Up, down, sideways, in and out. That gives you compression, stretching, twisting, bending, and I probably missed a direction or two. There is no simple replacement.

    [​IMG]
     
  13. El_Guero

    El_Guero Previous Member

    The craft is two oversized canoes (war canoes) lashed together on 5 crossbeams and supported by a platform in the middle, the platform is basically a large raft.

    Looks like an oversized day cruiser.
     
  14. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Treated pine in Australia is renowned for being a quite poor structural timber.

    Do the plans actually specify radiata pine, or some other sort of timber ?
     

  15. El_Guero

    El_Guero Previous Member

    I agree with you. I think even 5 poles would struggle. Possibly the reason they then lay down the 2x4" platform?

    Plans are not published, I don't think.
     
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