Damage case guideline

Discussion in 'Stability' started by kiddo14, Apr 7, 2015.

  1. kiddo14
    Joined: Apr 2015
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    kiddo14 Junior Member

    Hello Everyone!!
    I want to know is there any specific reference about how create a damage case for damage stability analysis.I think just randomly selecting two or three tanks not gonna work. There must be a definite guideline about how to choose the tanks and compartments for damage case. I have studied MARPOL regulation 28 about subdivision and stability and also gone through the SOLAS subdivision and stability. But did not find anything concrete. Also read the IACS Unified Interpretations about the scope of damage stability but did not got the answer.
    So if any one does know about how to select the tanks for a damage case , then please share. Does damage extent has anything to do with this. I am only a student and first time doing damage stability . so please help!!
     
  2. TANSL
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    TANSL Senior Member

    Unfortunately the only solution there is to study all possible cases to check which one results in the worst conditions. The study of the floodable length, however, can give an idea of what compartments may be the most dangerous. But unless the opinion against some experts, I think you have to consider all possible cases. Given, of course, if the damage is one or two compartments.
     
  3. kiddo14
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    kiddo14 Junior Member

    @TANSL thanks for your reply.Did you mean i should randomly damage one or two tanks and check the result to see what is the worst case ?
    Does damage extent play any role here ? i see a way is been described in MARPOL Reg 28 to calculate damage extent. What role does it play ? Is it for MARPOL oil outflow calculation ?
     
  4. TANSL
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    TANSL Senior Member

    In my opinion you have to study every case and check that the worst of them all stability criteria after damage are met.
    The extent of damage will tell you if a damage will flood one compartment or more at the same time.
     
  5. NavalSArtichoke
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    NavalSArtichoke Senior Member

    It's not clear for what type of vessel and service you want to perform damage stability calculations. Damage stability regulations vary somewhat between vessel types.

    If you are looking in the MARPOL, then I presume you are dealing with some sort of tankship.

    The length of the tankship will determine the extent of damage which must be applied to the vessel:

    1. For tankers with L > 225 m, damage must be applied anywhere in the ship's length
    2. For tankers 150 m < L < 225 m, damage must be applied anywhere in the ship's length, except for the machinery space. The machinery space is treated as a single flooded compartment.
    3. For tankers where L < 150 m, damage is assumed to take place between transverse bulkheads only, except for the machinery space.

    For evaluating the extent of damage to be applied to the vessel, there are three dimensions which must be calculated based on the particulars of the ship.

    For damage to the side:
    1. longitudinal extent is (1/3)*L^(2/3) or 14.5 m, whichever is less
    2. transverse extent is (B/5) or 11.5 m, whichever is less, measured inboard from the ship's side at the Summer Load Line.
    3. vertical extent is from the baseline upwards without limit.

    (Note: L and B for the vessel will be defined elsewhere in the SOLAS or MARPOL regulations.)

    Separately, for damage to the bottom of the vessel, see IACS Guideline No. 110:

    http://www.iacs.org.uk/document/pub...s_and_recommendations/pdf/rec_110_pdf1168.pdf

    Read this entire document and understand it thoroughly.

    You'll want to take your vessel's General Arrangement Drawing and the hull structural plans and using the extents of damage required, as discussed above, figure out which compartment or compartments will be damaged, and develop a list of damage cases to investigate.

    There may be a dozen or more different cases for a particular ship for side damage, and several different cases for bottom damage, if required.

    If your vessel plans are on CAD, you can create diagrams showing which compartments are flooded for each case, but even if CAD plans are not available, make some sort of diagram to illustrate the nature of the damage for others who review your calculations.

    It helps to prepare a "damage box" which has the same length and width as the extents of damage for your particular vessel. The "damage box" can then be moved around the general arrangement and structural drawings to help identify which compartment or compartments will be damaged at a particular location along the length of the vessel.

    Most regulatory and classification authorities require that ALL possible damage scenarios consistent with the damage extents be investigated, so randomly picking compartments to damage will not be sufficient.

    You should organize your damage cases in some manner, say starting at the bow and working your way aft to the stern. The results of your damage stability study will be quite voluminous, and you should prepare summaries of the important results for those reviewing your work.
     
  6. kiddo14
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    kiddo14 Junior Member

    Thanks NavalSArtichoke. Now i have a pretty good idea where to start from.
    Though i have a question to ask why bottom damage is considered separately(Specially in tankers ) ? I mean if you have a L-shape Wing and Double bottom tank (Most common in tankers now for segregated ballast purpose) a damage in side or bottom will have the same result. I mean the entire tank will be considered as damaged , right ? so why considered them separately as side or bottom ? is it because during bottom damage extent the damage box may extend toward the Cargo oil tanks ?
     
  7. TANSL
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    TANSL Senior Member

    With some tanks distribution a bottom damage can flood tanks that are not flooded with any side damage.
    You must take into account the extent and depth of the damage. A side damage, with its limited depth, will not reach some compartments that buttom damage, with same depth, does reach.
     
  8. NavalSArtichoke
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    NavalSArtichoke Senior Member

    I agree with what TANSL said about bottom damage in the previous post.

    It's hard to comment about the damage cases which might be developed for a particular vessel without considering its internal arrangement.

    That said, side damage and bottom damage are considered separately not only because of the arrangement of a vessel, but also because different bottom damage requirements are specified based on the DWT of the vessel, which are not easily correlated with the side damage extents. Also, the width of damage to be considered for bottom damage is usually taken about the centerline of the vessel, where most side damage would not be considered to occur.

    As always, the regulatory authorities also caution that should damage to a lesser extent result in a worse residual stability condition, then the stability from that lesser extent of damage must also be calculated and considered.

    If stability is worse during an intermediate stage of flooding before equilibrium is attained, then that intermediate condition must be evaluated also.

    For vessels assumed to be damaged in the loaded condition, any loaded cargo tanks which are breached must have a certain outflow or runoff of cargo assumed, depending on the density of the cargo relative to that of the surrounding water.
     

  9. kiddo14
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    kiddo14 Junior Member

    Thanks NavalSArtichoke and TANSL.
     
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