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.

TEST
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

Labels:

Comments

Post a Comment

Popular posts from this blog

Bilge Injection Valve

Bilge Injection is a valve that enables the engine room bilges to be pumped out directly overboard in the event of an emergency such as flooding. The valve is normally fitted to the end of a branch connection with the main sea water suction line. This enables large main seawater cooling pumps to be used as a bilge pump in an emergency. Emergencies like fire and flooding involve the use of seawater. If there is a fire, seawater is the biggest resource of water available in the sea. Similarly, if it involves flooding of the engine room, cargo spaces or any other place on the ship for that matter; you would again require pumping the sea water out of the ship. In both these cases, you require pumps.  There are two valves in close proximity namely main injection valve and bilge injection valve. Both of them have their own independent controls. The diameter of the bilge injection valve is kept nearly 66% of the main valve diameter which draws water directly from the sea th...
Post a Comment
Read more

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...
14 comments
Read more

Why do we blow through engine before starting ?

The engine is blown through on air before starting it : a) To Blow out through indicator cock any residual exhaust gas or     other products of combustion trapped inside the cylinder after     shutting the engine. b) To check if any jacket cooling water from cylinder head or     turbocharger or any other source, has leaked while the engine          was shut and collected on top of piston. If while blowing                  through, water comes out of indicator cock or relief valve, we          need to investigate and rectify the fault before starting the                engine. It is imperative that the engine is blown through before        starting. There have been cases where the generator engine has        been started from control room without bothering to blow     th...
15 comments
Read more