Bollard Pull Calculation Tool

Calculate the bollard pull of your vessel with this free interactive tool. Enter your vessel specifications below to get accurate results and visual analysis.

Vessel Type

Total Engine Power (kW)

Propulsion Type

Propeller Diameter (m)

Number of Propellers

Hull Efficiency Factor

Thruster Efficiency Factor

Water Density (kg/m³)

Comprehensive Guide to Bollard Pull Calculation (Free Excel Template Included)

Bollard pull is a critical performance metric for tugboats, offshore supply vessels, and other workboats that require significant towing or pushing capability. This measurement represents the pulling force a vessel can exert when moored to a fixed structure (like a bollard) at zero speed. Accurate bollard pull calculation is essential for vessel design, operational planning, and safety assessments.

Why Bollard Pull Matters in Maritime Operations

The bollard pull value directly impacts:

Towing capacity: Determines the maximum weight a vessel can safely tow
Maneuverability: Influences how effectively a vessel can position other ships or structures
Operational safety: Ensures the vessel can handle expected loads without engine overload
Regulatory compliance: Many ports and offshore operations have minimum bollard pull requirements
Fuel efficiency: Helps optimize engine performance for specific operational needs

The Physics Behind Bollard Pull Calculations

Bollard pull (BP) is fundamentally determined by the interaction between propeller thrust and hull resistance. The basic formula considers:

Engine Power (P): The total power output of the vessel’s engines in kilowatts (kW)
Propeller Efficiency (η): Typically ranges from 0.5 to 0.7 for most marine propellers
Thruster Efficiency (η_t): Accounts for mechanical losses in the propulsion system
Hull Efficiency (η_h): Considers how the hull design affects thrust (typically 0.95-1.05)
Propeller Diameter (D): Larger diameters generally produce more thrust at low speeds
Water Density (ρ): Saltwater (~1025 kg/m³) provides slightly more resistance than freshwater (~1000 kg/m³)

The simplified bollard pull formula used in our calculator is:

BP = (P × η × η_t × η_h × K) / (D × n)

Where K is an empirical coefficient based on propeller type and loading conditions.

Key Factors Affecting Bollard Pull Performance

Factor	Impact on Bollard Pull	Typical Range/Values
Propeller Type	Fixed pitch generally has higher bollard pull than controllable pitch at zero speed	Fixed: 1.00 Controllable: 0.90-0.95 Azimuth: 0.85-0.92
Number of Propellers	More propellers can increase total thrust but may reduce individual propeller efficiency	1-4 for most tugs Up to 8 for large OSVs
Propeller Diameter	Larger diameter increases thrust at low speeds (bollard condition)	0.8m – 4.5m for commercial vessels
Hull Design	Affects water flow to propellers and overall efficiency	Tugs: 0.95-1.05 Specialized: 1.05-1.15
Engine Loading	Engines optimized for low-speed high-torque perform better for bollard pull	70-90% load for max bollard pull

Step-by-Step Bollard Pull Calculation Process

For manual calculations (or to verify our calculator results), follow these steps:

Determine Total Available Power:
Sum the continuous rated power of all engines at the specified RPM (usually 100% MCR). For example, two 2000 kW engines provide 4000 kW total power.
Calculate Effective Power:
Multiply total power by mechanical efficiency (typically 0.95-0.98 for direct drives, 0.90-0.95 for reduction gears).

P_effective = P_total × η_mechanical
Apply Propulsion Efficiency:
Multiply by propeller efficiency (η_p) which varies by type:
- Fixed pitch: 0.55-0.65
- Controllable pitch: 0.50-0.60
- Azimuth thrusters: 0.45-0.55
Account for Hull Interaction:
Apply hull efficiency factor (η_h) which can enhance or reduce thrust:
- Open stern tugs: 1.00-1.05
- Conventional hulls: 0.95-1.00
- Specialized designs: 1.05-1.15
Calculate Thrust:
Use the thrust equation: T = (P × η) / v, where v is advance speed (zero for bollard pull). For bollard condition, we use empirical coefficients based on propeller loading.
Convert to Bollard Pull:
Final bollard pull is typically 80-95% of static thrust due to various losses in the mooring condition.

Common Mistakes in Bollard Pull Calculations

Avoid these errors that can lead to inaccurate results:

Using rated power instead of continuous power: Bollard pull should be calculated using continuous rated power (usually 90% of maximum rated power)
Ignoring mechanical losses: Forgetting to account for gearbox and shafting losses (typically 3-10%)
Incorrect propeller efficiency: Using generic values instead of manufacturer-specific data
Neglecting hull interaction: Some hull designs can increase effective thrust by 5-15%
Wrong water density: Using freshwater values (1000 kg/m³) for saltwater operations
Overestimating propeller diameter: Actual effective diameter may be less than nominal due to clearance requirements

Bollard Pull Standards and Certification

Several international standards govern bollard pull measurement and reporting:

Standard	Organization	Key Requirements	Typical Applications
ISO 10648	International Organization for Standardization	Standardized bollard pull measurement procedures	Commercial tugs, offshore vessels
IMCA M 202	International Marine Contractors Association	Guidelines for DP vessel capabilities including bollard pull	Offshore support vessels
OCIMF	Oil Companies International Marine Forum	Tug capability guidelines for tanker operations	Port tugs, escort tugs
ABR Guidelines	American Bureau of Shipping	Classification society rules for tugboat design	Newbuild certification

Certified bollard pull tests are typically conducted in controlled conditions with:

Calibrated load cells or dynamometers
Minimum 10-minute duration at maximum pull
Documented environmental conditions (water temp, salinity, current)
Witnessed by classification society surveyors

Free Excel Template for Bollard Pull Calculations

While our interactive calculator provides immediate results, many professionals prefer working with Excel for more complex scenarios. Below is a description of how to build your own bollard pull calculator in Excel:

Input Section:
Create cells for:
- Total engine power (kW)
- Number of engines
- Propulsion type (dropdown)
- Propeller diameter (m)
- Number of propellers
- Hull efficiency factor
- Water density (kg/m³)
Efficiency Lookup Tables:
Create tables with efficiency values for different propulsion types and hull designs. Use VLOOKUP or XLOOKUP to automatically select the right values based on user input.
Calculation Section:
Implement these formulas:
```
=B3*B4*VLOOKUP(B2, EfficiencyTable, 2, FALSE)*B5*B6/(B7*B8)
                
```
Where B3-B8 are your input cells and EfficiencyTable contains your lookup values.
Results Section:
Display:
- Calculated bollard pull (kN and tons)
- Effective power after losses
- Thrust coefficient
- Comparison to standard vessel classes
Visualization:
Add a simple bar chart comparing your vessel’s bollard pull to industry standards for similar vessel types.
Validation Checks:
Add data validation to ensure:
- Engine power is within reasonable ranges
- Efficiency factors stay between 0 and 1
- Propeller diameter is realistic for the vessel size

For a ready-made template, you can download our free Bollard Pull Calculator Excel template which includes all these features plus sample data for common vessel types.

Advanced Considerations for Professional Applications

For naval architects and marine engineers, several advanced factors may need consideration:

Propeller-Vessel Interaction:
Advanced CFD analysis can model how the hull affects water flow to the propellers, sometimes increasing thrust by 10-20% through proper design.
Dynamic Positioning Integration:
For DP vessels, bollard pull needs to be considered alongside thruster allocation and redundancy requirements.
Environmental Factors:
Current, wind, and wave conditions can significantly affect achievable bollard pull in real-world operations.
Engine Performance Curves:
Actual bollard pull may vary at different engine loads. Some vessels achieve maximum bollard pull at 85-90% MCR rather than 100%.
Propeller Cavitation:
At high thrust loads, cavitation can reduce efficiency. Specialized propeller designs can mitigate this.
Vessel Trim:
The angle of the vessel in the water affects propeller immersion and thus thrust production.

For these advanced calculations, specialized software like:

MAXSURF (by Bentley)
ShipFlow (by FLOWTECH)
ANSYS CFD
Star-CCM+

is typically employed, often requiring thousands of computational hours for accurate simulations.

Real-World Bollard Pull Requirements by Vessel Type

Different operational profiles require varying bollard pull capabilities:

Vessel Type	Typical Bollard Pull	Primary Operations	Key Considerations
Harbor Tugs	20-80 tons	Ship docking, berthing assistance	High maneuverability more important than raw power
Escort Tugs	60-100+ tons	Tanking escort, emergency response	Must maintain pull at higher speeds (4-10 knots)
Offshore Supply Vessels	100-300 tons	Anchor handling, towing rigs	Often require dynamic positioning capabilities
Ocean Going Tugs	150-400+ tons	Long-distance towing, salvage	Must maintain pull in open ocean conditions
Icebreaking Tugs	100-250 tons	Arctic operations, ice management	Specialized propeller and hull designs

When selecting a tug for a specific operation, it’s common to require 20-30% more bollard pull than the calculated requirement to account for environmental factors and safety margins.

Authoritative Resources on Bollard Pull:

For official standards and research:

Frequently Asked Questions About Bollard Pull

How is bollard pull actually measured?

Bollard pull is measured by securing the vessel to a fixed structure (bollard) or ground tackle with a load cell in line. The vessel applies maximum thrust while the load cell records the force. Tests typically run for 10+ minutes to ensure stable readings.

Can bollard pull be increased after a vessel is built?

Yes, through several modifications:

Upgrading engines for more power
Installing larger or more efficient propellers
Adding thrusters or azimuthing drives
Modifying the hull to improve water flow to propellers
Optimizing the propulsion control system

However, major modifications may require reclassification of the vessel.

How does bollard pull relate to free-running speed?

There’s generally an inverse relationship – vessels optimized for high bollard pull (with large propellers and low-speed engines) typically have lower free-running speeds, while vessels designed for speed have lower bollard pull capabilities.

What’s the difference between bollard pull and towing capacity?

Bollard pull measures static pulling force at zero speed. Towing capacity considers the vessel’s ability to maintain speed while towing, which depends on both bollard pull and the vessel’s resistance characteristics at speed.

Are there international standards for reporting bollard pull?

Yes, ISO 10648 provides standardized procedures for bollard pull measurement and reporting. Most classification societies and port authorities require bollard pull to be certified according to this or equivalent standards.

Conclusion: Optimizing Your Bollard Pull Calculations

Accurate bollard pull calculation is both a science and an art, combining fundamental physics with empirical data from real-world operations. Whether you’re designing a new vessel, evaluating an existing one, or planning complex towing operations, understanding these principles will help you:

Select the right vessel for your operational needs
Optimize vessel performance for specific tasks
Ensure safety margins are adequate
Comply with regulatory requirements
Make informed decisions about vessel modifications

Our interactive calculator provides a solid starting point, but for critical operations, we recommend:

Consulting with a naval architect for vessel-specific analysis
Reviewing classification society guidelines for your vessel type
Conducting physical bollard pull tests when possible
Using specialized software for complex hydrodynamic modeling
Maintaining conservative safety margins in all calculations

For those looking to deepen their understanding, we recommend exploring the resources from the authoritative organizations linked above and considering professional development courses in marine propulsion systems.

Bollard Pull Calculation Excel Free