Preliminary Still Water Bending Moment

Discussion in 'Class Societies' started by marufuddin0, May 7, 2021.

  1. TANSL
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    TANSL Senior Member

    I don't think it is necessary to write to anyone, what DNV-GL says is totally correct and, as it could not be otherwise, I agree with them. Don't you understand that it is impossible for a boat to be both hogging and sagging at the same time? I think I'm not going to continue this conversation until you realize that you need to dig a little deeper into the concepts of naval architecture and that common sense is very useful most of the time.
    Cheers.
     
  2. Scarf
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    Scarf Junior Member

    Where did I say that hogging and sagging occurs simultaneously?
     
  3. TANSL
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    TANSL Senior Member

    What does "bending momen to to include both" mean for you?
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    It is clear to anyone.

    Scaf said:

    This means when calculating the bending moment for hogging he is refereeing to vertical plane for longitudinal distribution....

    upload_2021-5-12_19-43-47.png

    and when refereeing to sagging he means also the same vertically..
    upload_2021-5-12_19-44-8.png

    This is basic naval architecture...
     
  5. Scarf
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    Scarf Junior Member

    to include both the sagging and hogging conditions, this doesn't imply that they occur at the same time, just that there are two conditions to consider.

    We'll leave it there, I sense that further discussion is not going to be fruitful and has strayed from the original thread topic.
     
  6. TANSL
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    TANSL Senior Member

  7. marufuddin0
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    marufuddin0 Naval Architect

    Thanks a lot for your contribution. Guys, so what I understand now (1) this rule book formula ( screenshot attached) value is only for preliminary calculation.

    upload_2021-5-13_4-53-44.png

    2. The maximum bending moment a midship can sustain is the design bending moment? This could be calculated from section modulus and material strength.
    3. Maximum Still water bending moment should be calculated from weight distribution and buoyancy curve. This is the thing I need to submit in the class.
    4. The design bending moment should be higher than the maximum still water bending moment.

    Could you please confirm if I am correct or wrong in the above cases?
     

  8. Ad Hoc
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    Ad Hoc Naval Architect

    Your "difficulty" stems from the fact that you are mixing and matching different methodologies/terminologies.

    In your notation:
    1. Is this from basic theory as per any text book... or just a citation from Class rules...
    2. This is what must be used - Class rules - because no matter what value you obtain in no.1, the values noted by Class will take precedent.
    3. This is related to no.1 and no.2 You may be required to calculate the weight distribution for classical theory values and/or Class rules. But what does the Class rule state for the methodology to use?

    So, you need to decide what route you shall take, to design the hull girder to satisfy given classical wave bending moments.

    Once you have decided, and satisfied said procedure...then and only then.. can you review from your own experience and fit-for-purpose, point of view.
    As this is totally different from Class rules, as this is not given in any Class rule.
     
    TANSL likes this.
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