BOLLARD PULL


Dear friends, over the years we’ve found interesting articles from different companies around the world, and we were recently involved in some trials, so we want to share some of the minimum requirements to obtain reliable results.

From the desktop of

Leonardo Montoya



Let’s start by its definition: BOLLARD PULL is the thrust developed by a vessel's propulsion system at zero speed. Since this test is usually conducted while the vessel is secured to a strong point on land, it is referred to as a "Bollard Pull".

There are several requirements that need to be met, and we mention some of them below:

  • Trial site: should allow the use of a long enough towing line and be free of wind, waves, and be located in very deep water with no tides or currents.

  • The towline length should be enough to allow free water astern of the vessel. (200 meters minimum recommended).

  • The tug has to be loaded to its designed waterline, in order to ensure the adequate immersion of the propellers.

  • Wind speed during the test should not exceed 5m/s.

  • The trial should be done with no currents if possible; if there’s a current, it should not exceed 1 knot.

  • Measurement should be taken using a calibrated dynamometer or a mechanical load gauge.

  • Steering during the trials should be avoided as much as possible.

  • The readings on the dynamometer should be continuously recorded by a computer, or at 30 sec intervals if a mechanical load gauge is used.

  • The maximum acceptable deviation of the dynamometer is +-2%.

  • Communication between shore and tug should be excellent, for an accurate recording of data relating the bollard pull to the rpm.
There are different terms of bollard pull:

  • Sustained Bollard Pull is the mean value of the pull during a specific time period (5 to 10 min.). If the measurements are taken every 30 sec., the sustained Bp is the mean value of the readings.

  • Maximum Static Bollard Pull is the highest 30 second value read during the test. If the measurements are taken every 30 sec., the maximum static Bp is the highest mean value of two consecutive readings.

  • Maximum Bollard Pull is the highest single value measured.

 

Loading cell during the test


Extractions from article presented in ITS 2002
in Bilbao by Steerprop.



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