Bollard pull tests determine the maximum tractive force a work boat can exert. They can be done practically or through simulation, but practical tests are cheaper and more widely used. However, they require specific conditions to be accurate. Simulated tests are more accurate but expensive and mostly used by large shipyards.
A bollard is a test, or rather the results of the tests used to establish the maximum tractive force that the work boat can exert. There are two ways to establish these values: practical tests and simulations. Practical tests involve physically attaching a measurement device to the boat and an immovable object and reading the resulting force when the boat is placed at full power. Simulation results are based solely on calculations performed in sophisticated software. Practical tests are not always accurate due to the large number of peripheral conditions that affect the results, while simulations are expensive and generally only used by large shipping companies.
Establishing the towing potential of ships, particularly tugboats, is considerably more complex than calculating the power of a land vehicle. There are many factors such as different powertrains, transmission types, and associated efficiency losses that make the usage powerplant output values inaccurate. Bollard pull tests give more realistic and representative results and are widely used to establish workboat pull values. Bollard pull-out values can be achieved in two ways: by simulation or by practical test.
Practical proof tests involve suspending a strain gauge on a marine cable that is connected at one end to an immovable object and at the other to the test vessel. Mooring bollards are often used as anchor points, which is where the tests get their name. When maximum thrust is applied to the boat’s motors, the amount of pulling force exerted on the cable is read from the meter. This is the cheaper of the two methods and is most often adopted by smaller boat builders for testing unique boats. However, this type of bollard test is difficult to perform accurately because there are a number of critical boundary conditions that must be met before the results can be considered definitive.
These factors include the use of a deep, undisturbed body of water without strong winds and currents for the test. Thrust must also be generated by the ships propeller alone and not aided by ricochet forces produced by adjacent obstructions. Propeller walk or the tendency of the propellers to guide the boat to one side must also figure into the equation. The relationship between the heights of the bollard and the cleat of the boats, as well as the geometry of the tow line, are also important factors. Even the salinity or salt content of the water plays a role in the precise measurement of the extraction values of the bollard.
Simulated bollard pull tests are simpler to perform but much more expensive than practical tests. These are pure mathematical calculations executed by highly sophisticated and accurate marine simulation software. The high costs of simulated bollard pull tests make this a more suitable option for larger shipyards producing boat lines. However, accurate as they are, simulated tensile tests are often supported by practical test test results.
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