Bollard pull is the motive or towing force a vessel is able to exert. A vessels bollard pull is determined experimentally during trials, by attaching a tow line to a shore-based bollard, and measuring the exerted force with a load-cell. The pull of the vessel is considered in metric tonnes, or imperial pounds.
When testing, the vessel should be situated in an area of minimal environmental activity (current, tidal flow, wind, wave, etc.) The water requires sufficient depth to limit shallow water effects. The directed flow of water from the propellers should be unconstrained by wharf, jetty, piers, etc. As bollards tend to be on shore, these conditions are rarely encountered. Where possible, the tug should be facing at a 45 degree to the corner of a wharf, at the maximum tidal extreme.
As the bollard pull will fluctuate, numerous measures are used to capture the vessels ability;
Bollard pull benefits from clean hull lines into the propellers, however most of the influencing factors are in the propellers themselves. High bollard pull is favored by;
The propulsion engine should have a closely matched torque curve, which is able to deliver sufficient power to develop maximum bollard pull values. It is common for engine manufacturers to sell matched drivetrains for bollard pull dependent applications, such as tugs.