Some questions about ISO 12215-5: 2019

Discussion in 'Class Societies' started by TANSL, May 7, 2021.

  1. TANSL
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    TANSL Senior Member

    The new version of this rule, which will make the previous one not usable beyond next June, raises, at least for me, some doubts. I would like to ask your opinion and share the possible doubts that you may have to see if, among all of us, we are finding explanations.
    For example, I ask my first question:
    6 possible work procedures are described but the two main ones, the "Simplified" method and the "Enhanced" method, are the two that this standard expressly serves. The first one is much simpler, faster, requires fewer calculations but, according to the standard, it is fully regulatory. Why then would a designer choose the Enhanced method if the Simplified is enough? What is the use of the designer being able to choose between one method and the other?. Who would choose the complicated method if the simple one is valid?
    Second question :
    Has anyone tried to use tables H2 ...... H7 and H8 to validate their own calculations ?. What have you achieved?

    Thank you very much for your opinions. I would like you to raise your doubts here as well.
     
  2. rxcomposite
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    rxcomposite Senior Member

    What is table H7 to H8?
     
  3. TANSL
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    TANSL Senior Member

    Table H.6 : Top hat worked example-Laminate preliminary
    Table H.7 : Top hat worked example-First part of analysis
    Table H.8 : Top hat worked example-End of analysis
     
  4. Alik
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    Alik Senior Member

    We have not tried 12215-5:2019 yet. But we already trying 12215-7:2020. There are few issues we found.
     
  5. Alik
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    Alik Senior Member

    For the 12215-5:2019, the way I see it:
    - program the NEW design pressures
    - use common laminate stack analysis (from previous versions of 12215-5) for practical calculations.
    - or use FEA for direct analysis with given design pressures.
    Otherwise, I don't see how it can be done. The standard is not user friendly and subject to interpretations.
     
  6. TANSL
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    TANSL Senior Member

    It is also not easy to understand. Surely it would not have been possible to do anything more complicated and impractical. But that is another subject that, for the moment, I have not studied in depth.
     
  7. TANSL
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    TANSL Senior Member

    Indeed. I contacted Mr. J.B. Souppez, creator of the rule, exposing some of my doubts. He told me that, when in doubt, he always resorted to theory. It is a totally correct and logical answer, but, if the situation is this, apart from obtaining the design pressures from the norm, what is the norm for? In most cases the designer knows very little about "theory" and for that, in my opinion, these rules are created, so that those who do not know the theory can make a correct, if not optimal, scantling. If the standard does not serve that type of "public", it would be better not to publish it, unless it is only a personal show of the creator of the standard.
    This being the sad situation is why I have proposed this thread, to see how others are managing. I think my SCT_2019 program reasonably solves many of these questions and could be, I hope, helpful to many designers.
     
    Last edited: May 7, 2021
  8. Ad Hoc
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    Ad Hoc Naval Architect

    I am a bit confused by this thread.

    If TANSL is offering a software that one must buy for a fee, a commercial licence, should not the author of the software understand the purpose of the rules they are asking others to buy?

    The user is free to interpret as they see best, but should not the author of the software know this question to offer guidance/advice to others using the rules/software?
     
  9. TANSL
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    TANSL Senior Member

    @Ad Hoc, with the respect you deserve me, I have to tell you that you don't know what you're talking about.
    I don't ask anyone to buy any rules. I understand this rule (ISO 12215-5:2019), I know where it has flaws, that they have them, and I correct them according to what the theory says. Why does your insane mind deduce that I do not understand what I am offering? What sovereign stupidity apart from the fact that you are judging or assuming things that you totally do not know and based on I do not know what dark intentions you are trying to discredit me. Is that the conduct of an honest professional?
    Thank you, however, for your always kind comments. I value them for what they are worth.
     
  10. Alik
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    Alik Senior Member

    There are many theories...

    I think once J.B. is not a practicing designer, he has time to play with theories. Our clients are paying us for the results - design the structure to pass the standard. Application of this and or that theory is always subjective. And the clients are not funding us to play with theories; the engineering time required by new generation of ISO standards is in disagreement with what the clients are ready to pay.

    Small boats are small money, thus engineering time should be reasonable, and rules clear and 'time saving'.
     
    Last edited: May 8, 2021
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  11. Ad Hoc
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    Ad Hoc Naval Architect

    Agreed.
    ISO is a total waste of space.
     
  12. Alik
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    Alik Senior Member

    OK so the practical question, if we use FEA for local strength, to ISO1125-5 or -7, now it is allowed.

    The slamming loads are defined for every panel and every stiffener, because obviously they depend on size of panel. This makes use of FEA not productive, because we have to apply load panel by panel, and stiffener by stiffener. With this approach, we can't apply load on two adjoining panels at the same time.

    Is there any way to apply all load to the entire bottom, or to apply 'impact spot' load to group of panels and stiffeners? Assume we take large part of the bottom as one 'dummy panel' (ignoring subdivision of that 'dummy panel'), calculate the impact pressure from the rulebook, and then run the FEA with that pressure? This way we can evaluate work of panels and stiffeners together...
     
  13. rxcomposite
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    rxcomposite Senior Member

    Agree. It is supposed to be simple with just adequate knowledge of boat design, not a rocket scientist. Graphs, nomographs, and tables should suffice if one wishes not to exercise their gray matter. FEA? Why? Even global strength analysis (hogging and sagging and hull section modulus and the likes) is NOT required for small boats.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    From your reply, that is most obvious. Since your reply has nothing to do with my question/query.

    Your thread HERE, is informing posters of the software you have created that is based upon said rule.
    And you state:
    Ergo you are selling your software for a fee. Because once the 30day period expires, one must pay.
    Thus you are engaging in a commercial enterprise with said software for financial gain.

    So if you have created a software based upon a set of known rules, how can you then ask:

    This suggest you do not understand the purpose of the rules. This being the case, why create software based upon rules you do not comprehend?

    ...and then finish by stating:

    So you are now asking users for money for your software, and yet.... at the same time asking... oh, can you please validate it for me with your calculations.
    This suggest you have no confidence in the software you have created (for financial gain) to produce correct results. Yet happy to take their money in using it.?!:confused:

    I don't see any such questions asked by other software creators such as HERE, at the Wolfson Unit.

    You can attempt to misdirect as is your MO, but the question is about what you are posting and offering.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    It really depends upon the objective.
    Is the purpose to do:-

    1 Pass the prescriptive set of rules
    or
    2 Design a structure that is fit-for-purpose.

    The two objectives are at variance with each other.

    It also depends upon how you wish the structure to be arranged, in terms of weight saving...which kind fo leads into items #1 and #2 anyway.

    The approach I have always taken, is to take the hull section with the greatest deadrise and spans...usually midships. Then design the structure to satisfy #1 and then apply #2 to this frame.
    And then adopt the arrangement to the whole vessel.

    Many will state, this is over engineering.. well, yes it is. But what is the objective.... #1 or #2.... and that's my point.
     
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