container ship cargo cog

Discussion in 'Stability' started by naserrishehri, Aug 24, 2012.

  1. naserrishehri
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    naserrishehri Senior Member

    i want too choose a COG point for cargo to calculate stability of a container
    ship.what point should be choose ?
     
  2. TANSL
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    TANSL Senior Member

    You can "choose" any point you want but it would be wise to define the distribution of containers, with loads of each, and that "you calculate" the center of gravity of the whole.
     
  3. gonzo
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    gonzo Senior Member

    You can go the opposite way. Determine what the highest COG is acceptable for the design, and indicate it.
     
  4. TANSL
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    TANSL Senior Member

    I fear that the calculation of the maximum allowable values ​​of KG is much more complicated than naserrishehri istrying to do. The first thing to define for that, among other things, is what are the criteria of stability that the vessel must comply. We must bear in mind, moreover, that it is not a single point but a curve which determines the maximum permissible value of KG, for each displacement
    But I think this is much more than knowing the center of gravity of a load, as I understand, is what naserrishehri need. Perhaps it is better, if that's what he needs, tell him how to calculate the c of g.
     
  5. naserrishehri
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    naserrishehri Senior Member

    i have considered COG of each container at the middle of container ,
    is it correct?
    because cog of cargo in container exist below middle point in actual.
     
  6. gonzo
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    gonzo Senior Member

    Not quite, container don't usually have a homogeneous load. I suppose that the average of a large number of containers may even out if you consider the COG to be in the middle. However, all containers have different loads, so they have to be weighed as they are loaded and then you can calculate the total COG. For example, you could have the first two layers with containers loaded to 8000 and the upper ones loaded to 13000. The COG may end up being too high for safety, even though the total load is below the maximum limit.
     
  7. naserrishehri
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    naserrishehri Senior Member

    i want to check IMO criteria for full load departure so you mean i must consider COG at the highest point that already i have calculated from MAX VCG analysis .
     
  8. ontwerp
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    ontwerp Naval Architect

    Classification societies generally recommend a per container VCG of 45%, homogeneously loaded. Some will also require a 50% vcg loadcase. For design purposes 45% VCG maximum TEU is a good loadcase to make. This loadcase will normally limit your design if it is a pure container ship.
     
  9. DCockey
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    DCockey Senior Member

    Is loading containers on a ship done in a manner to control the CG location?
     
  10. naserrishehri
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    naserrishehri Senior Member

    if always heavier containers put below lighter containers , then we can
    consider cog of each container in the center of volume of container.
    is it correct?
     
  11. TANSL
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    TANSL Senior Member

    A container ship not completely empty his load in a port and reload on the same port. It charges what he can in a port, moves to another port, where download any container (or not), loads (if possible) other containers, and so from port to port. Therefore, assuming that the heavier containers are in one place or another is totally incorrect. The actual center of gravity of the ship must be calculated considering the center of gravity of each container as closely as possible. It seems a conservative choice to estiamte the cog of "each container" at 50% of its height. If, in addition, it is true that the Classification Societies recommend using 45% of the height (which I doubt it), then all the better.
    The stability of a container is a very serious calculation that must to be done properly. There are no "shortcuts" in the calculation.
     
  12. gonzo
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    gonzo Senior Member

    There are enough examples of container ships capsizing at port while loading or unloading. The captain must take into consideration the real loads and not just a calculation made at a design office.
     

  13. Crowsnest
    Joined: Jun 2012
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    Crowsnest Junior Member

    Hi all.
    Its a long time ago from my last post, may be years. Hence, as I think nobody remembers me with my actual nick (crowsnest) or the former one (Ekaiztea), this, can be taken as my first post on Boatdesign.net.
    Well. lets go for the subject:
    When planning a loading operation for a container ship, a lot ofn factors are taken into account.
    If its a medium big ship, CG of containers is supposed at 50% of the TEU or FEU height/lenght.
    For ittle ships, a better approximation is required.
    Factors:
    Loading/Discharge harbour schedule.
    Cargo must be able to be discharge at its destination port without other containers interference.
    Cargo nature (Classification) of each container attending to segregation and compatibility between goods.
    Container weight, size and type. 20 or 40 ft, flat rack, open top, .... etc.
    Final and transitory Ships CG, seakeeping and navigation conditions.
    Ships structural concerns. Stacking points, Shear stress, bending moments.
    Togheder with all above:
    Minimization of times, loading means and harbour facilities.
    Maximization of ships capacity.

    Regards
     
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