Answer
The bollard pull test measures the maximum static pulling force a vessel (such as a tug or trawler) can exert at zero forward speed under full power.
Pre-requisites and Environmental Conditions
Water Depth: Minimum water depth beneath the keel should be at least equal to the draft of the tug, or ideally 2 times the draft, to avoid propeller stream recirculation or shallow water effects.
Clearance: Clear area around the vessel. Distance from the bollard to the stern should be at least two ship lengths.
Weather & Sea State: Wind speed should ideally be <5 m/s (10 knots). Current must not exceed 1 knot in any direction. Calm sea state with no significant swell.
Draft & Trim: The vessel must be at its design displacement draft, ideally with even keel or slight stern trim to ensure total propeller immersion.
Instrumentation & Setup
A calibrated electronic load cell (with backup mechanical gauge) is inserted in the towline.
The towline must be strictly horizontal or parallel to the water level (an angle >10∘ requires a cosine correction factor).
Continuous data logging of time, RPM, torque, fuel consumption, and pull force is maintained.
Test Procedure & Metrics
Warm-up: Bring the machinery to operating temperatures.
Maneuver: Move to the testing area and secure the towline to a certified onshore bollard.
Data Recording: Slowly increase engine power to maximum RPM. Once the pull stabilizes, continuous readings are recorded for at least 10 minutes.
Key Outputs Determined:
Maximum (Bollard) Pull: The highest peak recorded during the initial stabilization phase.
Continuous Bollard Pull: The average certified pull maintained steadily over the 10-minute period (this is the value stated on the certificate).