ISO 12215-5, Area pressure reduction factor, why Panel Area in denominator?

Discussion in 'Class Societies' started by Mariotti, Apr 2, 2021.

  1. TANSL
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    TANSL Senior Member

    Thanks, @rxcomposite for your post # 12. As always, concise, clear answers and directly to the bottom of the question.
     
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  2. Ad Hoc
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    Ad Hoc Naval Architect

    I suspect this is a language thing. Since no one is required to use a smaller value.

    Have you worked through the whole process, as noted in my previous post. By that I mean, you have satisfied the minimum requirements in 10.6.2, for example?
     
  3. Mariotti
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    Mariotti Junior Member

    Yes, you are right. I should have said minimum required thickness.
     
  4. Mariotti
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    Mariotti Junior Member

    Yes, I already had all the limits and bounds in my Excel-Sheet.

    Actually I wanted to make a decision on the material for the cat, so I needed the scantling for the weights and costs.

    I’m not sure the ISO-12215 (in the 2008 version) is the right tool for that. They state in the foreword:

    The scantling requirements are based principally on providing adequate local strength. Serviceability issues
    such as deflection under normal operating loads, global strength and its connected shell and deck stability are
    not addressed. The criteria contained within may need to be supplemented by additional considerations
    deemed necessary by the designer of the structure.


    So probably for the first estimations I’m better off with a rough guess. The Lwl of the cat is 22 ft

    The options are:
    1. GRP with polyester and fiberglass mat
    2. Balsa/Epoxy Sandwich with stitched fiberglass fabrics
    3 Plywood coated with Epoxy and stitched fiberglass fabrics

    So I would use for the first guess.
    1. 1800 g/m^2 fibre mass, frame spacing 600 mm
    2. 9 mm Balsa, 600 g/m^2 fibre mass outside and inside, frame spacing 1000 mm
    3. 6 mm Ply, 300 g/m^2 fibre mass, frame spacing 1000 mm

    Any thoughts on that?

    I favor the GRP because it is easier to maintain. That is also what all the small fisher boats here use so it should be cheap too.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    On what, the material selection, or the applicability of the rules, or something else?
     
  6. Mariotti
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    Mariotti Junior Member

    On the guessed scantling and frame spacing for GRP, Balsa/Epoxy and Plywood/Epoxy/Glass for a 22ft catamaran.
     

  7. Ad Hoc
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    Ad Hoc Naval Architect

    On a 22ft boat.... well, what do you think??

    Is 200mm or 2000mm better?....or somewhere in between?
    As the designer, that is your choice and to calculate the effects of your selection to establish the cost as well as any weight differential.

    That's called ... design!
     
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