Skip to main content

Bollard Pull

Bollard pull is a conventional measure of the pulling (or towing) power of a watercraft. It is defined as the force (in tons or kilonewtons (kN)) exerted by a vessel under full power, on a shore-mounted bollard through a tow-line, commonly measured in a practical test (but sometimes simulated) under test conditions that include calm water, no tide, level trim, and sufficient depth and side clearance for a free propeller stream. In another words Bollard pull is the maximum pulling capacity of a tug that can exert.

Why in  Bollard Pull not BHP?
The BHP of the tug is not sufficient to show the efficiency because of loss in transmission, propulsion efficiency and propulsion type Whereas Bollard pull shows the efficiency of the maximum pulling capacity of a tug that can exert.

Bollard pull test is carried out by dynamometer comprised of load cell & load indicator.
Loadcell is the force measuring link and it is made as part of the rope, connected to the towing hook. 

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.

Requirements for  the Bollard Pull Test:
  • The test is carried out at slack water
  • 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).
  • Water salinity must have a well-defined value, as it influences the specific weight of the water and thereby the mass moved by the propeller per unit of time.
  • 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.
  • Conditions must be static. The engine power, the heading of the ship, the conditions of the propeller discharge race and the tension in the towing line must have settled to a constant or near-constant value for a reliable measurement.
  • 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.
  • Bollard and the towing hook should be at the same height


Popular posts from this blog

Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division  IMO Symbol B Class Division  SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships. The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. Types of Divisions: "A" Class "B" Class "C" Class "A" Class: "A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria: They are constructed of steel or equivalent material They are suitably stiffened They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. they are insulated with approved non-combustible materials such that the average tempera

Load Line & Why it is Important

Merchant ships have a marking on their hull know as the Plimsoll line or the Plimsoll mark, which indicates the limit until which ships can be loaded with enough cargo, internationally, the Plimsoll line on a ship is officially referred to as the international load line. Every type of ship has a different level of floating and the Plimsoll line on a ship generally varies from one vessel to another.  All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line. There are two types of Load line markings:- Standard Load Line marking – This is applicable to all types of vessels. Timber Load Line Markings – This is applicable to vessels carrying timber cargo. These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background/black on a light background.  The comp

Pump Shaft Alignment Procedure

Types of shaft alignment methods: Visual Line-Up Straightedge/Feeler Gauge Rim and Face Cross Dial Reverse Dial Laser Visual Line-Up The visual line-up method is the most common method of alignment. Used in initial installations, visual line-up allows technicians to analyze the working conditions and feasibility of installation. Straightedge/Feeler Gauge Straightedges are used to determine the offset between coupling halves. Corrections are made under all four of the machines feet. Feeler gauges or taper gauges measure the gap between coupling halves at the bottom and top of the coupling. Rim and Face This method is similar in principle to using a straightedge and feeler gauge, but more accurate since dial indicators are used. The rim reading measures the offset between the coupling halves. The face reading measures the angular difference between the faces of the coupling. Changes are calculated with the same formula as the straightedge/feeler gauge met