Transverse Stability at Large Angles of Heel

Discussion in 'Stability' started by mcm, Mar 28, 2017.

  1. mcm
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    mcm Senior Member

    Remind me, is 20 and 30deg of heel or is 25 and 30deg usually used when calculating basic transverse stability at large angles of heel?
     
  2. TANSL
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    TANSL Senior Member

    Maximum righting arm for an heel angle >= 25 °, preferably greater than 30°.
    Maximum GZ = 0,2 m for heel angle> = 30º

    But there are several more criteria to be met, which vary, though not much, depending on the type of boat.
     
  3. mcm
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    mcm Senior Member

    Thanks TANSL!
     
  4. Mermaid Co
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    Mermaid Co Junior Member

    that highly depends on kind of vessel. For normal ships stability range is checked for 40 degree or downflooding angle whichever is lesser. and max gz shall not occur before 25 degrees. For OSV range of stability is same but max gz shall not occur before 15 degrees and for barges that range is 15 degree.

    You can refer to IS code for details. or can read here for some idea

    http://www.mermaid-consultants.com/drillship-maxvcg-and-stability-calculation.html
     
  5. TANSL
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    TANSL Senior Member

    Mermaid Co, You should specify that when you talk about 40 degrees, or the angle of flood, you mean dynamic stability because otherwise it does not make sense.
    At this moment I do not remember what is the IS code but stability, in general, is governed by the IMO code (damage stability, SOLAS 2009).
     
  6. Mermaid Co
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    Mermaid Co Junior Member

    IS code is Intact stability 2008 code which governs most of the stability calculations of the boats and ships which are more than 24 m in length. That is part of IMO.For basic intact stability calculation there are few points to check

    1. Area ratio
    2. Angle of max GZ
    3.Minimum GM
    4.Angle of downflooding

    etc.

    So whatever I have mentioned is for intact stability check but you are referring to damage stability code....that is another part where minimum angle of flooding for weathertight openings are checked.
     
  7. TANSL
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    TANSL Senior Member

    I have wrongly expressed my self. Intact stability is governed by IMO Resolution A.749 (18).
    In addition to the criteria you mention, there are some others that must also comply with all ships and others applicable to certain types of ships.
    I repeat again that when you write "For normal ships stability range is checked for 40 degree or downflooding angle whichever is lesser", you may refer to the dynamic stability because otherwise it would not make any sense. and "minimum angle of flooding" must be checked for intact and for damage stability. If an opening is watertight, it should not be taken into account as a flood point. Let's not confuse anyone. Stability criteria must be checked with all watertight openings, closed.
     
  8. Mermaid Co
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    Mermaid Co Junior Member

    The code you are mentioning,was update and replaced by MSC resolution and 2008 IS code is latest. Please find attached for clarification.

    I was just talking about angles to comply with latest stability criteria irrespective of of static or dynamic stability. If you go through general and weather criteria of this code,you will get it
     

    Attached Files:

  9. TANSL
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    TANSL Senior Member

    Mermaid Co, as I understand it, resolution MSC.75 (69) is not a stability code as such, but merely amendments to resolution A.749 (18), which is a very different thing. That is, in my opinion, there is no new code of stability. MSC is no more than a committee that has adopted the IMO / SOLAS stability criteria. Nor is there, in my opinion, an MSC stability code.
    There are several stability criteria, for initial stability, for GZ value, for dynamic stability, as well as other criteria depending on the type of vessel (and I am not talking about weather criteria). What you were saying had only to do with the third case.
    But I think if the OP needs something more concrete, he will tell us. At the moment I'm going to worry about more interesting things. By the way, you are developing a very complete advertising campaign.Although I do not think this is the medium nor the right way to carry it out, I wish you much success with it.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    This week a large cyclone descended on NE Australia causing much havoc, and brought the unusual sight of large sailing boats moored in marina pens heeled over maybe 25-30 degrees by nothing more than wind pressure from a powerful gale on their beam, acting on the masts and rigging.
     
  11. Mermaid Co
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    Mermaid Co Junior Member

    TANSL, I was just referring to latest code,As IS code 2008 has some significant inclusions for OSVs,MODU and other type of vessels compared to A749. However I would insist not to confuse with this statement If an opening is watertight, it should not be taken into account as a flood point. Let's not confuse anyone. Stability criteria must be checked with all watertight openings, closed.

    I didnt write watertight in my previous post but weathertight which shall be considered in damage stability. watertight points are not considered anywhere in stability calculations because they are designed for pressure head.
    Hope it will not create any confusion.
     
  12. TANSL
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    TANSL Senior Member

    You're right, you have not talked about watertight openings. I thought it was a mistake because I do not understand what you mean with "weathertight openings".
     
  13. mcm
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    mcm Senior Member

    You're right, sorry I should have mentioned the kind of vessel. In this case a monohull sailboat.
     
  14. TANSL
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    TANSL Senior Member

    Type of vessel does not refer to the type of hull or its motorization, but to the type of work developed by the ship, cargo, container vessel, fishing vessel, passage, ...
     

  15. Mermaid Co
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    Mermaid Co Junior Member

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