Bollard Pull Estimator
Estimate static bollard pull using installed power, efficiency, and propulsor type factor. This tool gives a practical planning estimate (not a class-certified test result).
What Is Bollard Pull?
Bollard pull is the static pulling force a tug can generate while secured to a fixed bollard on shore. It is usually reported in tonnes-force (t), but you will also see kN in technical documentation. For tug operators, port planners, and marine engineers, bollard pull is one of the quickest ways to compare towing capability.
In practical terms, a higher bollard pull means a tug can exert more force to move, hold, or control another vessel at low speed or during harbor maneuvers.
How This Calculator Works
This calculator uses a widely accepted estimation approach based on available propulsion power and correction factors:
- Convert input power to kW (if needed)
- Apply overall propulsive efficiency
- Apply a propulsor type factor
- Apply optional derating/sea margin
- Convert effective power to estimated bollard pull using a baseline constant
Formula Used
Estimated BP (tonnes) = Effective Power (kW) / 74.57
Where:
- Effective Power = Input kW × (Efficiency/100) × Propulsor Factor × (1 − Derating/100)
- 74.57 kW per tonne-force corresponds to an approximate 100 hp per tonne rule-of-thumb baseline.
Why Use an Estimate Instead of a Single Fixed Rule?
Many quick checks use “100 hp = 1 tonne bollard pull.” That can be useful, but real-world performance changes with hull design, nozzles, propeller diameter, gearbox losses, and operating condition. Including efficiency and propulsor factor makes the estimate more realistic for feasibility studies and early design comparisons.
How to Use This Bollard Pull Calculator
- Enter installed engine or shaft power.
- Select whether your value is in kW or hp.
- Set overall propulsive efficiency (start with 70% if unknown).
- Choose the propulsor factor closest to your tug configuration.
- Add derating if you want a conservative estimate.
- Click Calculate Bollard Pull.
Typical Bollard Pull Ranges
- Small harbor tug: 20 to 35 t
- Mid-size ASD tug: 40 to 70 t
- Large terminal/escort tug: 70 to 100+ t
These are broad ranges. Always compare against manufacturer sea trial and certified bollard pull test results when available.
Important Factors Not Captured
- Shallow-water effects and current
- Propeller-hull interaction details
- Engine load limits and thermal constraints
- Condition of hull/propeller and fouling
- Towline angle, winch setup, and operating technique
FAQ
Is bollard pull the same as towing force at speed?
No. Bollard pull is a static test value at (near) zero vessel speed. Towing force underway depends on hydrodynamics and operating speed.
Can I use brake horsepower directly?
Yes. Select hp in the calculator and it will convert automatically to kW.
Is this suitable for contract guarantees?
No. Use this for planning and education. Contract, class, and insurance decisions should rely on certified data and formal naval architecture analysis.
Final Note
If you are selecting tugs for port operations, combine this quick bollard pull estimate with maneuverability data, winch capability, and local environmental requirements. A balanced specification is usually more valuable than maximizing a single number.