ISO 12215-7 Global Loads Case 5

Discussion in 'Class Societies' started by TANSL, Dec 13, 2021.

  1. DCockey
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    DCockey Senior Member

    Did you mean "Since kg is a mass, it can be converted to Newtons or kN force."
     
  2. rxcomposite
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    rxcomposite Senior Member

    Not exactly. It is ISO that referred it to a mass expressed in kg. Reading the ISO rule further they referred to "displacement volume VD volume of displacement of the boat that corresponds to the appropriate loading condition, taking the density of water as 1 025 kg/m3 NOTE Displacement volume is expressed in cubic metres."
     
  3. rxcomposite
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    rxcomposite Senior Member

    Last edited: Dec 14, 2021
  4. TANSL
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    TANSL Senior Member

  5. rxcomposite
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    rxcomposite Senior Member

    In common use, the mass is referred to as its weight. ISO refers to the mLDC as the mass of the boat in loaded condition expressed in kilograms.

    Where I am confused is that it is asking it to be expressed in Newtons (or kN) not kGf. Since as stated above, "a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth" and the mass is multiplied by a number, is ISO looking for inertial property (longitudinal force)?
     
  6. TANSL
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    TANSL Senior Member

    I use mLDC in kN and the results obtained seem correct. What worries me now is why it is necessary to select the lesser of two forces, one of which is always less than the other.
     
  7. rxcomposite
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    rxcomposite Senior Member

    Because in the example it is a cat so two hulls not one. 1 of the 2 hulls is the lesser assuming it is a symmetrical hull.

    I do not know what the formula is used but I have a clue since the boundaries are in g's and is denoted as deceleration. Must be the opposite of vertical acceleration which is also measured in g's.
     
    Last edited: Dec 15, 2021
  8. TANSL
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    TANSL Senior Member

    In the case of a trimaran, the mass (or weight) mLDC is compared with the mass (or weight) of a float (see picture in post #1) :

    FLT = min (5 mLDC; 5 mFLOAT) (kN)
    But I think it is better to leave it for the moment because we are thinking about the same thing. If at some point I find the explanation for this comparison, I will tell it right away (in case someone, other than me, is interested).
     
  9. rxcomposite
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    rxcomposite Senior Member

    Just pick the smaller of the two or three.
     

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  10. TANSL
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    TANSL Senior Member

    mLDC is the full load boat mass (or weight) that is always greater than one hull or one float mass (or weight). Hence my doubt.
     
  11. Alik
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    Alik Senior Member

    TANSL, for sure this is a mistake in the standard.
    But acutally, we have never calculated this case yet. It is only applicable to craft with shord bridgedeck, so we don't care.

    Regarding the case itself, I doubt if it is useful, as it does not count acceleration of impact which will depend on speed.
     
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  12. Alan Cattelliot
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    Alan Cattelliot Junior Member

    Hi,

    Officially, there is indeed 2 main questions :
    - what is the purpose of this case ? there is no clear indication of speed, which would be a minimum when considering the question of impact.
    - what are these numbers & funny formulas...
    I have no idea. I ask the question to our national representant on the subject : 3 words.

    "No one knows. (But there should be a mistake)"
     
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