bollard pull

Discussion in 'Boat Design' started by jollyricard, Mar 17, 2012.

  1. jollyricard
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    jollyricard Junior Member

    Dear all,

    My name is Riccardo. I want to ask you an important question; what is the test procedure during Bollar pull on board PSV VESSEL?
    I think that IT is obtained connecting the towing hook to the bollard,......
    the towing hook is always fitted on this type of vessel or there are alternative ways for this particular test?


    Many thanks in advance
    kind regards
     
  2. CDK
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    CDK retired engineer

    The towing hook is connected to a scale attached to a bollard, so you can read the amount of force.
     
  3. jollyricard
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    jollyricard Junior Member

    Dear CDK,

    many thanks for answer, but someone told me that for bollard pull is necessary appropriate winch, is this possible?
     
  4. CDK
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    CDK retired engineer

    I guess we're talking about the same thing here, a rather large mechanical device that shows on a dial how much force is applied to it.
    When I did the test I could not find the proper equipment, so I used an array of thin ropes with known breaking strength and cut them one by one until the boat tore the rest. That gave an idea about the prop thrust, but it was also a bit dangerous. It is better to find a scale with sufficient capacity. They are used with cranes and are calibrated in tons.
     
  5. Submarine Tom

    Submarine Tom Previous Member

    Clever guy.

    I wonder how much your thrust varies at speed...

    -Tom
     
  6. CDK
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    CDK retired engineer

    That is much more difficult, if not impossible. You could pull another, larger boat and measure the tension in the rope, but the drag from the pulling boat itself cannot be measured, so such a test doesn't prove much.
     
  7. murdomack
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    murdomack New Member

    Nowadays they tend to use a thing called a load cell on cranes, I have seen them used testing winch pulls as well. It gives a digital reading of the load and you can get ones that radio transmit the data to a handheld unit allowing you to keep well away.

    Jollyricard,
    As already said by CDK the Bollard Pull test does not need a winch.
    However, using the available Bollard Pull in open water service conditions needs an elaborate winch as the towing line should be controlled at all times. Some very expensive cargoes being towed for long distances on barges have ended up adrift because the barge has got caught in a tide race and the towline has snagged the seabed and snapped. This is a nightmare scenario for a tug crew.
    The winch automatically responds to changes in tension in the wire and gives the tug some time to respond.
     
  8. MikeJohns
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    MikeJohns Senior Member

    CDK

    Shaft torque measurements are common using radio transmitter strain gauges and you can work from the torque and derive thrust from the prop data.

    A direct method sometimes possible is to shim apart a coupling at the thrust block and apply a radio strain gauge directly to the flange.


    Jollyricard

    For Bollard pull as Murdomack posted a load cell is used. The load cell and measuring equipment are shore based and the Tug is sent off with a line around twice its LOA. You should be ale to find procedures for conducting the test in some of the published Class or Flag requirements.
     
  9. baeckmo
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    baeckmo Hydrodynamics

    ......Still another method where the engine is mounted on rubber blocks is to use a load cell to measure the thrust directly on the engine block. The load cell may be statically calibrated during a bollard pull test. Admitted, its no space tech, but it works fine with decent repeatibility, and you are not depending on radio transmission, glue in a damp environment et c.

    Now, any measurement of shaft thrust alone leaves the propeller-hull interaction unattended, so the interaction factors have to be found by other means.
     
  10. J Feenstra
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    J Feenstra Junior Member

    Another question, what is a good method to calculate the bollard pull?
     
  11. Godofredo
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    Godofredo New Member

    Riccardo

    The bollard pull test is done with one line connected to a bollard in one end, and to a tension measuring device with enough capacity in the other end that is in some way connecte to a strong structure of the boat (a wire rope connected to the towing hook could be). As a reference rule, think in 15 kg/hp. To choose the apropiate instrument. But to that, you have to add an extra 50% as a margin for the instrument because the bollard pull generates pulse loads. It is not a static load. The instrument could be like the ones used to test cranes, with instant readings, or an instrument with the capacity to register the load every second or so, for within a few minutes, so you get a continuous register. It is also possible to build a testing device, using a thick plate with strain gauges. I have done that procedure once.

    Regards

    GAP
     
  12. Godofredo
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    Godofredo New Member

    Riccardo

    The bollard pull test is done with one line connected to a bollard in one end, and to a tension measuring device with enough capacity in the other end that is in some way connecte to a strong structure of the boat (a wire rope connected to the towing hook could be). As a reference rule, think in 15 kg/hp. To choose the apropiate instrument. But to that, you have to add an extra 50% as a margin for the instrument because the bollard pull generates pulse loads. It is not a static load. The instrument could be like the ones used to test cranes, with instant readings, or an instrument with the capacity to register the load every second or so, for within a few minutes, so you get a continuous register. It is also possible to build a testing device, using a thick plate with strain gauges. I have done that procedure once.

    Regards

    GAP
     

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  13. DCockey
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    DCockey Senior Member

    Also keep in mind that the bollard needs to be firmly anchored. The pull of the vessel is supposed to be test, not how secure the bollard is.
     
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