Simplified Scantling Formula

Discussion in 'Boat Design' started by Thomas Ask, Oct 30, 2005.

  1. Thomas Ask
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    Thomas Ask Junior Member

    I am seeking a simple formula or rule of thumb for determining scantling in solid fiberglass structures. What I have is rather elaborate and I need something basic for a marine surveying book I am writing.

    Also, if anyone has interesting photos relevant to marine surveying (such as broken structural features and the like) I would be interested in receiving them. Appropriate photo credits would be provided.

    Thank you for your assistance.

    Regards

    Tom
     
  2. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Dave Gerr has one really simple in his book "The nature of boats". It's based on the length of the boat + a minimum thickness. I don't remember exactly, but it was simething like
    Hull thickness in mm = 0.8 x LOA in m + 3,
    something like that...
     
  3. oceanmaster66
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    oceanmaster66 Junior Member

    Take a look at Dave Gerr's "The Elements of Boat Strength", you can get a copy from amazon.com
     
  4. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I must mention that Gerr has been the subject for a few disputes here, some think that he makes rules that are not based on very scientific or engineering principles.
     
  5. Thomas Ask
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    Thomas Ask Junior Member

    Bases for Gerr?

    Thanks for the notes, I am familiar with Gerr's book but I have no idea what it is based upon. He relates the scantlings to LOA, Beam and draft plus freeboard. This would work as a rough value but I dont know if it is derived from something or rooted in his own experience.
     
  6. yokebutt
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    yokebutt Boatbuilder

    Applied theology?

    Yoke.
     
  7. chandler
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    chandler Senior Member

    Actually I think it's based on dispacement.
     
  8. Alik
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    Alik Senior Member

    We developed easy-to-use method for estimation of structure, based on ISO12215 series calculations. Please, try and comment.
     

    Attached Files:

  9. Deering
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    Deering Senior Member

    Ran a few quick calcs with it and it yields results that seem reasonable. I'm not a NA so forgive my ignorance on the terms.

    Not sure what is being measured in "plate width". Define "pate" in this application.

    When you say that the formulas apply to boats with "common proportions", would a catamaran hull apply? Or too high of a L/B ratio?

    Your coefficients are for sailing and planing hulls. Where does a displacement powerboat hull fit in?

    Stiffener length - is that the distance between frames?

    It would be helpful to put these into an Excel spreadsheet instead of a Word doc.

    Thank you!
     
  10. Alik
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    Alik Senior Member

    Terms are defined in ISO12215 or any other up-to-date structurel rule. Plate width is smaller size of shell plate. Stiffener length is unsupported length of stiffener: a) for longitudinals is distance between frames b) for frames length is defined using schemes, generally length of floor and 'top timber'.
    For displacement boats coefficients for sailboats can apply - at least I hope so. These formulas are not intended for multihulls and can be used only for monohull boats L/B<3.5. This paper will be presented in full at TEAM2005conference in Sinagapore.
     
  11. Thomas Ask
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    Thomas Ask Junior Member

    Thanks

    Thanks for the feedback. I would like to look this over and get back with you.

    Regards, Tom
     
  12. Thomas Ask
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    Thomas Ask Junior Member

    Looks Interesting!

    Alik,

    This looks very interesting. Thanks for sharing it and I am interesting in including this. Has the been subject to peer review? Is it based on a curve fit of data?

    If you wish to correspond directly, feel free to contact me at:
    task@pct.edu or task@askandassociates.com

    Regards, Tom
     
  13. Willallison
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    Willallison Senior Member

    Where are these discussions that you refer to? I don't recall seeing anyone dispute the validity of Gerr's scantling calc methods...
    Many - including Gerr himself - will tell you that they yield conservative scantlings that are based on a combination of rule-of-thumb and engineering principles...
     
  14. Alik
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    Alik Senior Member

    I just replied by e-mail.
     

  15. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

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