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Thread: Continuous Shipunloader -v- Grab unloader

  1. #1
    Helmut Mayer

    Helmut Mayer

    Director and Principal Engineer

    Mayer International Group Pty. Ltd.

    Mayer International Group Pty. Ltd.

    Continuous Shipunloader -v- Grab unloader

    (On behalf of another member)

    I am looking for articles, editorials, technical material, back-up documents from end-users, etc., concerning efficiency (ship time) of Continuous Ship Unloaders (CSU) vs. Grab Unloaders.

    In fact I have noticed that a few years ago, manufacturers were estimating a 75-85% efficiency for CSU vs some 50-55% for grabs. By contrast, more recent documentation shows a 65-70% for CSU vs some 55-60% for grabs.

    In other words it seems that in the first half of '90 the efficiency of CSU was somehow overestimated while the grab efficiency increased in the last decade thanks to electronics, etc.

    Is anyone aware of any good literature on the issue, or has any direct experience with this?
    Last edited by HelmutMayer; 20th December 2001 at 21:41.

  2. #2
    Helmut Mayer

    Helmut Mayer

    Director and Principal Engineer

    Mayer International Group Pty. Ltd.

    Mayer International Group Pty. Ltd.
    75-85% operating efficiency (design rate/achieved rate over a ship) is an ambitious efficiency most organisations aim for, but many do not achieve, especially for unloaders.

    It sounds to me like the original figure you saw was a theoretical figure based on the operation of the machine itself, together probably with cleanup (less for a CSU than a Grab). However, as time went by, this figure has had to be updated to account for the many other factors that influence efficiency, including such intangiables as operator efficiency (varying from operator to operator). Other factors still, derive from the efficiency of downstream equipment that may be matched more or less well to the unloader itself.

    From my experience, but without having any literature or formal (and broad) studies to back this up, I generally take 70% as being a real life figure to work with. With some good initial and ongoing effort, higher figures can be achieved, but you probably should not plan on it.

    There is no doubt that the last 10 years has indeed seen good advances in the way machines are controlled and this has benefitted the grab unloaders. This, together with the fact that the grab is typically the lighter machine, seems to have given the grab a new lease on life.
    Helmut Mayer
    B.E.-Aerospace B.Sc.-Psyc
    Director and Principal Engineer
    Mayer International Design Engineers Pty Ltd
    Specialist Engineering of Material Handling Equipment,
    Cranes and other Custom Machines

  3. #3
    Author Guest

    Continuous Shipunloader versus Grab Unloader

    The efficiency of both types of unloading can not be given as a percentage
    without more detailed information.

    The efficiency is highly depending on the size of the ship, the construction
    and assistance of front end loader(s) during the clean up stage.

    To our opinion grab unloading efficiency has not increased due to
    electronics. An experienced operator still works quicker without than with
    electronics. The spillage and dust control, however, has been reduced thanks
    to the electronics.

    Kind regards,

    Hans van Est

  4. #4


    We have used a range of CSUs, mechanical and pneumatic. These have been both shipborne (Siwertell, Norstrom) and land based (Kovako) pneumatics. The efficiency depends on a wide variety of variables other than the machinery alone. For example if one uses a Siwertell for the bulk loading and discharge of cement the efficiencies are much greater than for an equivalent cargo of alumina.This is because of the differential stresses on the bearings.

    The other constraints include whether the hatches have to be open for loading or discharge as the weather factor is often far more important than the equipment's capabilities. This is magnified on sea-to-sea transfer as the slewing of the towers in the wind prohibts a range of operations. With mechanical unloading there is far less problems than with pneumatic if interruptions to the flow occur because of weather, moving from hatch to hatch or opening and closing hatches. When one stops a pneumatic system it requires a great deal of extra pressure to blow against a head of product in the line.

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