Angle of GZmax

Discussion in 'Stability' started by Abhilash Satheesan, Jan 11, 2018.

  1. Abhilash Satheesan
    Joined: Jan 2018
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    Hello Friends!

    I'm totally new to this forum and i am looking forward to have great discussions. I work as Naval Architect and i am currently preparing preliminary stability booklet for a ferry boat. I use Maxsurf to do it and modeled hull in rhino.
    So, while running various load-cases my angle of GZ maximum comes up to be same in all load-cases. Is this something which is not supposed to happen? However, the GZ maximum value differs in each cases. Please let me know if needed more information. I will be happy to share it. Thank you
     
  2. TANSL
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    TANSL Senior Member

    Could you upload your maxsurf files, with load conditions, to have a look?
     
  3. Abhilash Satheesan
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    Abhilash Satheesan Junior Member

    as attached
     

    Attached Files:

    • Hull.msd
      Hull.msd
      File size:
      654.5 KB
      Views:
      63
  4. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

  5. Abhilash Satheesan
    Joined: Jan 2018
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    Im sorry. Attached should have it
     

    Attached Files:

    • Hull.msd
      Hull.msd
      File size:
      654.5 KB
      Views:
      53
  6. TANSL
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    TANSL Senior Member

    There are no load cases here either. Send me a text file with the loading conditions and I will include them in Maxsurf.
     
  7. Abhilash Satheesan
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    I dont know why, but i was able to open it good. Anyways, i have attached an excel file. hope it should help. Did you have the compartments?
     

    Attached Files:

  8. TANSL
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    TANSL Senior Member

    No, I do not have the compartments either. Send me all the files that you have in the folder of your ship.
     
  9. Abhilash Satheesan
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    it doesn't allow me to upload .hml file here that have all my loadcases. Thats why i gave to excel sheet which as all values and you could insert by yourself into maxsurf stability module to define compartments
     
  10. TANSL
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    TANSL Senior Member

    You can generate a .zip file. I could define compartmments if you give me their data but it will be a tedious work.
    When trying to calculate the first load condition, the program warns that the trim of the boat is too large. It is probably because the origin is not well located and, therefore, the longitudinal distances of the gravity centers of the various items are not correct. Can you check this?.
    In any case, the variation in the KG is very small among the three first load conditions, so the GZ curves should be very similar.
     
  11. Abhilash Satheesan
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    alright. hope attached zip will work. I understand there is little variation in KG. But im getting exactly 20 deg where GZmax happens in all loadcases. I doubt something is wrong.
     

    Attached Files:

  12. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I think everything is fine and that the program calculates well. The problem could be that the hull does not have enough stability for the weight it must carry. In my opinion, but it is only my opinion, that hull is not suitable for the purpose for which you want to use it.
     
  13. Abhilash Satheesan
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    Abhilash Satheesan Junior Member

    As per IMO, the boat fails intact stability. But the boat has only to meet US coast guards special requirement which is far more relaxed that IMO. its meeting their stability criteria but this contact angle of GZmax seems weird to me. Anyways, i haven't found any reference to such as issue on the internet. Asked some of friends, they too said its very rare and not sure about this. Anyways, thank you for having a look at it and for your comments. You may let me know if you happen to figure out in future.
     
  14. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I do not believe, that is to say, I am sure that the USCG is not more relaxed than the IMO. Check your criteria well.
    Your hull seems to have been obtained from a hull for a recreational boat, perhaps through a scale change, and I sincerely doubt very much that it is suitable for a 300-passenger vessel.
    The problem is not that the maximum GZ angle is the same in all loading conditions. The problem is that the maximum GZ is produced at 20º of heeling with which the boat (being a monocoque) does not meet any criterion of stability
     

  15. Abhilash Satheesan
    Joined: Jan 2018
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    Location: Rhode Island

    Abhilash Satheesan Junior Member

    I am following CFR 170 and 171 sections. Its pretty much relaxed. Hey and i just figured out why its all 20 degrees exact. the heel angle interval was 20deg. Now i ran each loadcases with 5 deg interval and it gave me different angles revolving around 20 deg. It took atleast 5 minutes to complete the analysis though. Do you wanna check and confirm
     
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