How to Select the Correct Mooring Bollard Capacity
Selecting the correct mooring bollard capacity is a critical part of designing a safe and reliable berth. A bollard must withstand the forces transferred through a vessel’s mooring lines while accounting for vessel characteristics, environmental loads, line configuration, operating conditions, and the supporting structure.
Simply choosing a bollard according to vessel size or deadweight tonnage is not enough. Mooring loads are influenced by wind, current, waves, tides, vessel geometry, line angles, and how loads are distributed across the mooring arrangement.
For ports, terminals, jetties, wharves, and marine facilities, the objective is therefore not to select the largest available bollard. It is to determine the appropriate rated capacity for the actual design loads and mooring conditions.
What Does Mooring Bollard Capacity Mean?
The capacity should not be considered in isolation. The complete load path includes:
Mooring Line → Bollard → Anchor Bolts → Concrete/Foundation → Quay or Berthing Structure
Every component in this load path must be capable of safely transferring the design forces.
This is particularly important because bollards are safety-critical components of marine infrastructure. PIANC guidance similarly treats the bollard or hook, its fixings, and its foundation as an integrated system rather than independent components.
1. Start with the Design Vessel
The first step is to establish the characteristics of the vessels expected to use the berth.
Important parameters may include:
Vessel type
Displacement
Length overall (LOA)
Beam
Draft and variations in draft
Freeboard
Above-water projected area
Underwater projected area
Mooring equipment and arrangement
Deadweight tonnage can provide an indication of vessel scale, but it should not automatically be treated as the required bollard capacity. The actual loading depends on the complete vessel, environmental, and mooring arrangement.
This becomes particularly important for facilities serving multiple vessel classes. Bollards should be selected for the governing design condition, not simply the vessel most frequently calling at the berth.
2. Evaluate Wind, Current, Waves and Tidal Conditions
A moored vessel remains exposed to environmental forces even after berthing.
The main loads typically considered include:
Wind
Wind acting on a vessel’s exposed hull and superstructure can generate significant longitudinal and transverse forces. For preliminary understanding, wind force may be represented by the simplified relationship:
F = ½ × ρ × C × A × V²
where:
F = wind force
ρ = air density
C = applicable wind force or drag coefficient
A = projected area exposed to the wind
V = wind velocity
Because force varies with the square of wind velocity, higher wind speeds can substantially increase the loads that must be resisted by the vessel’s mooring system.
For final bollard selection, however, wind loading should be determined using the applicable marine design standard, vessel characteristics, wind direction, site conditions, and project-specific mooring analysis.
Current
Current acts primarily against the vessel's submerged area. Vessel draft, current direction, berth configuration, water depth and hull geometry can all influence the resulting load.
Waves and Swell
At exposed berths, waves and long-period swell can produce vessel motions and varying line tensions that require more detailed analysis.
Tides and Water-Level Changes
Changing water levels alter the vertical angle and geometry of mooring lines as the vessel rises and falls relative to the berth.
ESC Marine Systems identifies wind and current forces, swell, waves, tidal forces, vessel draft changes, line characteristics and line angles among the important considerations when selecting a marine bollard.
The total environmental force acting on a vessel is not necessarily the load applied to a single bollard.
3. Understand the Mooring Arrangement
The vessel is secured through a system of:
Head lines
Stern lines
Breast lines
Spring lines
Their orientation determines how effectively they resist longitudinal and transverse vessel movement.
The designer should therefore evaluate:
Number of active mooring lines
Number of lines attached to each bollard
Line spacing
Horizontal and vertical line angles
Vessel fairlead locations
Bollard positions
Mooring line properties
Expected line pretension
Load sharing between lines and bollards
Poor geometry can result in uneven load distribution and place significantly higher demand on individual mooring points.
4. Check Mooring Line Loads and Angles
The angle at which a mooring line approaches a bollard matters.
A bollard rated for a particular load is designed around defined loading conditions. High horizontal or vertical line angles can change the force components acting on the bollard, anchoring arrangement and supporting structure.
This is also one reason different bollard designs are available.
ESC Marine Systems currently offers configurations including T-Head, T-Horn, Kidney, Cleat, Single Bitt, Double Bitt, Pillar, Japanese-style designs and Tricorn bollards.
For example, T-Head bollards are used across a broad range of mooring applications, while ESC notes that T-Horn configurations can accommodate comparatively steep mooring angles. Kidney bollards can provide an economical option where high-angle line handling is not a primary requirement.
This means bollard type and bollard capacity should be selected together, not as separate decisions.
5. Determine the Required Rated Capacity
Once the environmental forces and mooring arrangement have been established, loads can be distributed through the mooring system to determine the governing demand at individual bollards.
The selected capacity should satisfy the applicable design criteria and project standard while considering:
Governing line load
Number of lines sharing the bollard
Horizontal and vertical load components
Applicable load or safety factors
Extreme operating conditions
Future vessel requirements where specified
For example, if engineering analysis establishes that a particular mooring point requires a capacity greater than a nominal 70-tonne bollard can safely provide under the applicable design criteria, the designer would move to the next suitable rated capacity and verify the complete bollard and anchoring system.
The final rating should always come from the project-specific mooring analysis and applicable design standard, rather than a simple vessel-tonnage lookup table.
6. Verify the Foundation and Anchor Bolts
Selecting a correctly rated bollard does not automatically produce a correctly designed mooring point.
The supporting structure must also resist the forces generated by the bollard.
Checks may include:
Anchor bolt tension
Anchor bolt shear
Concrete breakout
Pull-out resistance
Concrete edge distances
Reinforcement
Base-plate bearing
Local structural capacity
Global quay, dolphin or deck capacity
This is particularly important when replacing an existing bollard with a higher-capacity unit. Installing a heavier bollard on the same foundation does not mean the mooring point automatically gains the higher capacity.
The supporting structure must be verified for the new loads.
7. Consider Material and Corrosion Protection
ESC Marine Systems lists material options including ductile cast iron and cast steel, with grades referenced to standards including BS EN 1563, ASTM A536, ASTM A27, ASTM A148 and EN 10293. Its listed anchor bolt options also include specifications under ISO 898, BS 3692 and ASTM F1554.
Material specification, coating system, inspection access and maintenance requirements should therefore form part of the bollard selection process rather than being considered only after capacity has been established.
8. Design to the Applicable Marine Standard
ESC Marine Systems states that its bollards are designed and manufactured with reference to international standards and guidelines including BS 6349 Part 4 and PIANC guidance.
The applicable requirements should be established early in the project because they can influence load cases, capacity, arrangement, material selection, anchoring and testing.
Mooring Bollard Capacity Range
ESC Marine Systems provides bollard configurations across a broad capacity range. Its published product information lists ratings extending from smaller 5-tonne cleat bollards through to bollards rated up to 300 tonnes, depending on configuration.
Available types include:
This range allows the bollard configuration to be matched to the required capacity, line geometry and operating conditions instead of relying on a one-size-fits-all solution.
Information to Provide When Requesting a Mooring Bollard
For preliminary bollard selection, providing good project information can significantly improve the quality of the recommendation.
Where available, include:
Vessel Information
Vessel type and size
Displacement or DWT
LOA and beam
Maximum and minimum draft
Mooring Information
Mooring arrangement or plan
Number and type of mooring lines
Line MBL
Expected line angles
Required bollard capacity, if already calculated
Environmental Information
Design wind speed
Current velocity
Wave or swell conditions
Tidal range
Berth Information
Quay, jetty or dolphin configuration
Proposed bollard spacing
Existing foundation details
Applicable design standard
Even a preliminary berthing or mooring layout drawing can provide valuable information for an initial technical review.
Final Considerations
Selecting the correct mooring bollard capacity requires more than matching a bollard rating to vessel tonnage.
A reliable design considers the complete system:
Design Vessel → Environmental Loads → Mooring Arrangement → Line Forces → Bollard Capacity → Anchoring → Supporting Structure
When these factors are evaluated together, engineers can establish a mooring solution that is both safe and practical without unnecessarily oversizing the equipment.
Planning a new berth or reviewing an existing mooring system?
Visit ESC Marine Systems to explore mooring bollard solutions and discuss your project requirements
