Structural design - some brief on approaches

Discussion in 'Boat Design' started by Alik, May 10, 2020.

  1. Alik
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    Alik Senior Member

    There is also a difference between Class Rules and ISO. Class Rules are in public domain. ISO are copyrigthted, so it is not possible to post parts of it on the forum.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Thanks for the conformation.

    Yes I am aware of annex D.. but as it states:

    "..Such assessment is outside the scope of this part of ISO 12215..."

    Thus, how do you apply global loads, as per ISO, if they state is is beyond the scope and no pass-fail limits for compliance are provided??

    That's what I don't understand.

    As for 6.2, it does not give criteria for pass/fail. As it states:

    "...ISO 12215-5 is based on the assumption that hull and deck scantlings are governed by local loads,...Annex D gives recommendations for the assessments to be made..."

    But annex D, as noted above, is not a pass fail set of rules as one sees in Class rules, it just says if your vessel falls under those cited, to perform a check. Ok.. but what rules do they say must be used - what pass - fail to use.
    None are given. Because ISO does not give any.

    That is what i don't understand, no guidance under ISO is provided.

    All annex D states is:

    "...The resisting structure to this bending moment shall be assessed in compression for the deck (generally the limiting factor in longitudinal strength analysis), or in tensile stress for the bottom or the keel..."

    That is not a pass-fail set of criteria to satisfy.
    It just goes on to provide some guidance on buckling checks - as it seems to focus only on buckling checks. There is far more to global stress analysis than simple buckling checks. Buckling in itself is not a catastrophic failure (but can be as 1 of several modes of failure), it can simply be a deck panel that 'pops' as you walk over it. Such issues are easily solved by adding an anti-buckling stiffer mid panel and it passes any local rule check. But it still does not address global stresses of the whole structure - a global bending moment check. It is far too simplistic, but that is to be expected as ISO is aimed at monohulls under 24m.

    Thus my point remains, there is no real global strength checks for a pass-fail in ISO as it is about small boats, all under 24m only.

    Noted.
     
  3. TANSL
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    TANSL Senior Member

    Nobody is talking about "a pass-fail set of criteria to satisfy."
    You are very good at your language (which does not have much merit), better than technique, which allows you to try to make believe that you were right, but you were not. Your "point does not remain", you were saying things that were not correct and that could be tricky, because you were talking about what you did not know. ISO 12215-6, like any other regulation, says that something must be verified, although it does not explain how to do it. Have you seen, for example (I know this is not the subject of this thread), that the Regulation a Classification Society says how to calculate the stability of a ship when it requests that certain stability criteria are met? In this case, ISO 12215-6 indicates that the longitudinal resistance should be checked and gives some formulas to calculate the maximum bending moment or the compression stress on the deck, which is enough to do the check. What more do you need ?. Because what the ISO does not have to explain is how to calculate the first moment of area of the main frame or similar things.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    If that is the case... what are you calculating??... how do you know it complies?

    So if you get no guidance how to do it - how do you know if it has passed or failed?...what is the unit of measure for compliance?
    Class rules provide compliance metrics, ISO does not.

    And the pass-fail criteria to check against is what??
    All is says in 6.2 is:

    "...an explicit longitudinal strength and buckling assessment is recommended...."

    Recommended only?!... please explain how this is mandatory??

    Because you sated:

    But your saying an assessment must be made..... but ISO only says it is just recommended. Both cannot be correct?!

    Well if that is your answer, then you do not know the rules which you cite:

    Annex D
    "...The following procedure is not intended to serve as a full longitudinal strength calculation..."

    There is far more to longitudinal and global strength calculation than a simple buckling check.
    If your position is to only perform this basic check for a global and longitudinal strength calculation, then clearly there is little point asking you any more questions, as this scope of analysis is beyond your usual practice for such vessels.

    Thank you for your clarification.
     
  5. Alik
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    Alik Senior Member

    TANSL, just ignore him, the way I do.
    He is a demagogue and is using his language advantage. But in reality, I see no sense and no real experience behind, when it comes to practical small craft design, especially in composite.
     
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  6. TANSL
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    TANSL Senior Member

    I`m not calculating anything. Don't try to confuse. I am only saying that you stated that ISO does not take longitudinal resistance into account, which is not true. You have affirmed it because, although you did not know the norm (I see that you have quickly begun to study this norm and now you cling to the literalness of the text as a limpet), you intended to show your "authorites" on that subject by giving a master class.
    To the rest of the turns that you give to the language, to the partially reproduced texts, to the deformation of the theme in order to distract attention from your error, I will not answer.
    Just apologize to @Alik for helping to destroy his thread. It was only intended to make clear that it is not true that ISO 12215 does not take account of, or that in calculations of scantlings on boats less than 24 m in length, longitudinal resistance need not be taken into account.
     
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  7. TANSL
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    TANSL Senior Member

    I would but I think he is an impostor (being a naval architect does not presuppose anything and showing us many pictures, none of his own and some of books from more than 40 years ago, indicates little practice and a worrying degree of obsolescence) and I try to expose him when I have the chance.
     
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  8. gonzo
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    gonzo Senior Member

    I think that the main thing to consider, is that if there is a legal requirement to comply with a Classification Society, it doesn't matter whether there are alternatives from the engineering perspective. Following those rules is mandatory. Some members seem to be missing that. I am not a lawyer. What I learn from the contract law classes in college, was that the law is what it is. There are no requirements for it to make sense or be the most efficient way of doing things.
     
  9. Alik
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    Alik Senior Member

    In most of the countries is no requirement for full class for most of commercial small craft, and for all recreational small craft.
    Small recreational craft is ISO, unless self-built for own use.
    Small commercial craft is a kind of 'grey zone'. Each country is different. Say, in Australia they accept ISO for hull structure up to 15m in length, coastal categories. Some countries will use class rules for structure.
    We use our own 'safety matrix' for preliminary design of those craft, and then negotiate with the maritime authorities of flag.
     
  10. gonzo
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    gonzo Senior Member

    There are countries, for example Argentina, that require plans to be signed and stamped by an engineer or naval architect. There is no minimum size for the requirement.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Oh dear, same old nonsense an misdirection.

    No, it does not.

    Well, what about this:-
    Agreed.
    And what does ISO state about it:

    So that is a no. It does not.
    It is outside the scope...it is assumed only local loads...and only recommends a check. This is not :

    So you do not understand the rules you claim to know. There is no MUST BE stated anywhere in ISO. It clearly states it is beyond the scope...and only provides recommendations if the vessels falls into set categories it lists, to be checked. Yet does not say how to check tor compliance of such.... and yes I do know the rules. It is easier to let the person making claims answer their own questions to ascertain if they understand what they are stating....... which in your case, you do not.

    But that is not surprising. Since you have stated previously:

    So, you claim to know the rules, but yet do not understand them. Unable to answer simple questions - perhaps because you do not understand what you're talking about and thus do not wish to be questioned on your statements. Any normal person would simple state yes or no, and yet you do not and cannot. And then whilst attempting to appear knowledgeable in a set of rules, perhaps in some lame attempt to appeal to others for some credibility in your comments, in the same breath you have nothing but utter disdain contempt and polemic comments for those that do quote the rules correctly.

    What a most strange person you are.
     
    Last edited: May 14, 2020
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Curious, when you state this:

    Which as noted above it does not, only says recommendations.... as it is out of the scope of ISO.
    Protestations to the contrary will not alter the text in ISO.

    And yet you also have stated this:

    Which supports that assessment that ISO does not cover global checks.

    Thus, i'm very confused by your constantly changing interpretation of the rules.

    And that is perhaps why.
    It seems you do not like to be questioned on your statements/claims that you have made yet contracted the very same statements/claims that you make on other threads.
     
    Last edited: May 14, 2020
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Correct.
     
  14. TANSL
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    TANSL Senior Member

    If you handled technical issues as well as you handle language, what a good naval architect you would be! (Obsolete ??? )
     

  15. DCockey
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    DCockey Senior Member

    There are no legal requirements for construction, strength, etc in the US for recreational boats and vessels carrying six or fewer passengers for hire (up to twelve passengers for hire for vessels over 100 gross tons) up to a very large size. The only legal requirements for stability and floatation for these boats only apply to a subset of recreational boats under 20 feet in length. Similarly many non-passenger carrying commercial vessels in the US such as tug boats, tow boats, barges and commercial fishing boats up to a large size are generally exempt from structural and stability requirements although a few years ago basic static stability requirements were applied to commercial fishing boats over 24 meters.
     
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