Grain Stability Bulk carrier

Discussion in 'Stability' started by Dr34m3r, Mar 5, 2015.

  1. Dr34m3r
    Joined: Mar 2012
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    Dr34m3r Senior Member

    Anyone have got done Grain stability calculation manually done and approved by class ?

    I think not all the software (except NAPA) is capable of doing the calculation. How you manage to calculate allowable grain heeling moment ? manually in the calculation , how to manage to find void space ?

    I have read the rules of Grain code.
     
  2. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    The Allowable Grain Heeling moments are calculated based on the righting levers for the vessel at a series of different drafts. The Grain Code shows what criteria are to be used with the righting lever curves to determine the values of the Allowable Moments. This is a relatively straightforward calculation to make, but it is tedious since it involves making calculations for a range of different displacements and vessel VCGs.

    The attached Stability Information Booklet for a typical bulk carrier shows the stability criteria and a table of Allowable Grain Heeling Moments.

    The trickier calculations are producing the grain heeling moments in each hold as a result of a shift in the grain cargo. The IMO Grain Code shows how to analyze the geometry of a cargo hold and establish the surface of the grain after it is loaded and manually trimmed. Once the volume of the void space above the grain has been determined, then the grain is assumed to settle in the hold and shift to one side in response to the rolling of the vessel.

    For each cargo hold, a curve of grain heeling moment versus initial grain capacity is produced for use by the ship's crew in calculating the total actual grain heeling moment produced by a given cargo loading.

    If the total actual grain heeling moment is less than the allowable grain heeling moment, then that loading condition is acceptable, assuming other conditions are met (draft, trim, intact stability, etc.)

    A booklet of this data and sample calculations is prepared to be appended to the vessel's regular stability documentation.
     

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  3. Dr34m3r
    Joined: Mar 2012
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    Dr34m3r Senior Member

    Thanks NavalSArtichoke !

    I have that docs froom google ! I am clear about the step of process to verify the criteria.


    I am not clear how you manually ( from autocad GA) calculate void space for each cargo hold. Specially when you have grain holes and upper deck girders .How you calculate void space when u have this holes and upper deck girders.
     

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  4. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Unlike the surface of a liquid in a slack tank, the top surface of a load of grain can assume a complicated shape, depending on the geometry of the hold, location of things like hatch beams and other structure, areas of the hold inaccessible for grain trimming, etc.

    It's hard to generalize and describe how to figure the shape of the void because holds vary so much in design. The best advice I can give is to study the Grain Code, because I was never able to find any other sources of information which described what to do.

    The angle of repose of the grain also comes into play, but the 30 degrees shown in your diagram is a reasonable value for most grain cargoes.

    The method I used when doing these calculations was to examine the layout of each grain hold and draw however many sections it took to get a good description of the cross section of the hold, not only in way of the hatch, but particularly at the ends of the hold fore and aft of the hatch.

    The tedious part comes after the grain has shifted to one side and you have to find the flat surface of the grain, keeping the void volume constant.

    My method came down to doing sketches and making capacity calculations of each hold after heeling, in order to determine the transverse center of gravity of the contents, which would then be used to calculate the actual grain heeling moment for the hold versus initial amount of grain in the hold, prior to shifting.
     

  5. Dr34m3r
    Joined: Mar 2012
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    Dr34m3r Senior Member

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