offshore marine services about bollard pull certification and trials
Bollard pull certification and Trials:In order to establish the pulling capacity of a towing vessel, a physical test of its capability may be carried out.
This test is referred to as the bollard pull trial or test.
It may be carried out when the vessel is a new building, when re-engined or has new rudder propellers fitted or for the purposes of satisfying a specific requirement of a contract of towage During bollard pull tests, the towing winch machinery may also undergo a variety of trials.
There are a number of methods and criteria for carrying out the test, but the basic aims are as follows:
1. Establish the maximum pulling capacity of the vessel when the engines are working at the manufacturer’s recommended maximum continuous RPM. In addition it is normal to test a new vessel at 110% Power Output ,in other words at 10% Overload in order to establish a maximum bollard pull value.
2. Establish the pulling force exerted at various settings of engine speed, propeller pitch or engine configuration.
3. Test the towing winch brake holding capacity with the winch drum full of wire and the vessel worked up towards maximum bollard pull.
4. Test the winch quick release mechanism when pulling at some predetermined, bollard pull, usually between 30% to 40% of maximum power. This test may be in two parts:
• testing the quick release mechanism when the winch is hauling in; and
• when the winch is riding on the brake.
5. Test any tow winch spooling gear. This test is carried out with the spooling gear engaged and the wire at an angle of about 60% off the boat’s centreline. The boat should be pulling at about the maximum continuous bollard pull.
6. Test the strength of fixed gog wire, guide pins or towing pods. This test is carried out with the tow wire at about 60 degrees each side of the boat’s centreline and pulling at or near her maximum bollard pull.
It is obvious that all the components, pulling points, tow wires, shackles and fittings should be certified and examined to ensure that they are strong enough to sustain the maximum expected loads.
An adequate safety factor of 10% to 20% is normal. An adequate Safety Factor of at least twice the maximum calculated loading is usally applied.
The conditions required for the test are briefly as follows:
1. The clear water distance between the stern of the boat and the point of attachment of the tow line should not be less than twice the boat’s length (BP) and ideally between 300 and 350 metres.
2. The water depth should be at least twice the boat’s maximum draught.
3. The test cell should have an accuracy of about ± 2% and have a certificate of calibration and remote reading and recording mechanism for the test cell is highly desirable.
4. The weather conditions should be calm with minimum wind, sea & current.
5. The boat should be at her normal operational trim and draught.