Changes in ISO 12217

Discussion in 'Stability' started by Guillermo, Sep 11, 2010.

  1. Guillermo
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    Guillermo Ingeniero Naval

    2009 ammendments to parts 1 and 3 of ISO 12217 have been released and a DIS document on part 2 is under revision.

    For this last several limits, tests, definitions and calculating methods have been altered, among them the way of calculating FDS factor in the STIX formula, to become

    FDS = (Agz / (15.81 * Lh^0.5))^0.3 (Note the new 0.3 power)

    Where:
    Agz to be calculated to AVS instead of the lesser of DFA and AVS as it was in the 2002 version.

    Furthermore minimum STIX for Category is proposed to come down from 32 to 31 and the one for Category B to be increased from 23 to 25.

    It seems there is no agreement between the members of the WG 22 and perhaps proposed changes will not come into effect.

    An alternative ammendment to the formula has been proposed, to change the constant from 15.81 to 19

    Anybody has more information or wants to comment on this?
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Quite a big change and I don't get sensible numbers compared to to the old FDS=Agz/(15.81 * Lh^0.5)
    Agz to be calculated to 90deg
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    Sorry.. was a bit hasty doing my spreadsheet :rolleyes:
    Now the numbers are ok.. I think it's now better practise to calculate the total positive area but the 0.3 power makes the affect to STIX value a bit too low IMO
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    There is a RORC study showing impact in STIX is estimated in a mere 3-5%
    I have to work out a couple of examples to check. Have you checked it with a some specific cases?
     
  5. TeddyDiver
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    TeddyDiver Gollywobbler

    Just with my own design with zero impact to STIX.
    (But that's kind of inbuild in the STIX formula that if there's nothing "wrong" with a specific feature it doesn't have any significant impact to the outcome)
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    I have checked for a 13,72 m length boat with a downflooding angle of 105º and 137º AVS and the STIX comes up from 52,3 to 59,3 for MOC condition

    A relevant change indeed, not matching with RORC's findings of a 3-5% impact. Where am I wrong?

    I attach both the current and altered versions of the STIX calculator for anybody to check them and post here results and comments.

    Thanks in advance.
    Cheers.
     

    Attached Files:

  7. Ad Hoc
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    Ad Hoc Naval Architect

    You may also like to know that that status of ISO 12215 Parts 1 - 9 Small Craft Structures is as follows:
    Parts 1 to 6 and 8 are now ISO standards but Part 5 is under continuing review by ISO TC 188 / WG 18.
    Part 7 is on hold.
    Part 9 Appendages is still under development, especially HTS fin keels. The masts and rigging requirements are moved to the new Part 10 for continuing development ISO 11336-1 Large Yachts Glazed Openings - Strength, Weathertight and Watertight Integrity Part 1 Independent Glazed Openings- Design, Construction, Testing is in the ISO / DIS stage now being reviewed by national standards organisations.

    FYI
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Thanks for the info John.
    Best regards.
     
  9. fcfc
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    fcfc Senior Member

    I fear missing parentehis. The 0.3 power should apply to the whole term, not not the divisor part only.
     
  10. fcfc
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    fcfc Senior Member

    (C22/(15,81*RACINE(C7)))^0,3

    unlimited FDS is now 1.077 instead of 22.210 and STIX down to 50.278, within 4% of the old one.
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Of course you're right!
    Here the corrected spreadsheet.
    Thanks a lot.
     

    Attached Files:

  12. Guillermo
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    Guillermo Ingeniero Naval

    Oooops!
    Friend Konstantin, from Russia, brings my attention to a bug in the FKR formula at the spreadsheet in my previous post.
    It says
    FKR = 0,875+0,0883*Fr (If Fr >=1,5)
    But it should be
    FKR = 0,875+0,0833*Fr (If Fr >=1,5)

    I attach here the corrected spreadsheet, as well as the one for the current ISO 12217-2:2002 in force.

    Thanks a lot Konstantin! :)
     

    Attached Files:

  13. fcfc
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    fcfc Senior Member

    From what I have heard, another change is the load condition: seems that there is a new "arrival" condition : as the full load case, but with all tanks 90% empty. This may be a little hard for boats with tanks in the bottom ...
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

    That does mean fuel and water tanks? Reckon not waste and ballast tanks?
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    All tanks that have 'consumables' inc any ballast tanks.
     
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