ballast draft

Discussion in 'Stability' started by abalkees, Feb 26, 2014.

  1. abalkees
    Joined: Dec 2013
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    abalkees Junior Member

    Hi,

    I am working on a project to optimize a tanker ship for both the laden journey and the ballast leg (return journey).

    My ship design draft is 12.18 m. I am wondering how to define the ballast draft for my design case and in general. IS there an assumption or an empirical method to get the ballast draft?

    any help please?
    Thx, Alaa
     
  2. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    The ballast draft usually depends on several factors.

    Lloyds Register used to have a formula for the minimum ballast draft at the bow for vessels it classed.

    In general, you want to ballast the vessel such that the propulsion and steering equipment are immersed so that they remain effective.

    In addition, since you have a tanker, you would check the bending moment and shear force to make sure the strength of the vessel is not endangered. Ballast can be shifted to suit this criterion.

    There may be other considerations, like seakeeping. Keeping a low GM will reduce motion accelerations in a heavy seaway. Slamming of the bottom near the bow might need investigating if it appears that a deep enough draft forward cannot be obtained with ballast.
     
  3. Vinassman
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    Vinassman Junior Member

    Hi abalkees,

    NavalSArtichocke pretty much said everything but I would like to ask one question: do you already have some bits of design for this tanker? You have a design draft so I guess you have a good idea of the general arrangement and the lightship weight, don't you?

    If so, you probably have already the volume of ballast. It might be a good starting point to try some combinations of ballast (such as ballast 1 + 2 + 3, 2 + 3 + 4, and so on) to see which one will give the best results in terms of bending moment, immersion, trim, stability, ...

    If not, try to get some references of tanker in the same range of deadweight so you know in what range of design draft you should be.
     
  4. babri
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    babri Junior Member

    In addition to what NavalSArtichocke mentioned, Also check the visibility of wheelhouse. Low draft and a little aft trim may cause increase obstructed field in front of the tanker above requirement of IMO rule or Canada channel regulation.
     

  5. abalkees
    Joined: Dec 2013
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    abalkees Junior Member

    many thanks all for your useful replies, and sorry for late reply.
    Alaa
     
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