Views: 425 Author: Nanjing Taidun Publish Time: 2026-05-19 Origin: Site
Content Menu
● What Are Single and Double Bollards? A Quick Refresher
>> Single Bollard (Single Bitt)
>> Double Bollard (Double Bitt)
● Head-to-Head Comparison: Single Bollard VS Double Bollard
● Selection Factor #1: Vessel Size and Mooring Load
>> How to Determine Required Load Capacity
● Selection Factor #2: Mooring Line Density and Configuration
>> Single Bollard — Best for Simplicity
>> Double Bollard — Best for Complex Mooring
● Selection Factor #3: Tidal Range and Water Level Variation
>> Which Bollard Handles Tides Better?
● Selection Factor #4: Spring Line Requirements
>> Single vs Double for Spring Lines
● Selection Factor #5: Space Constraints
● Practical Scene Selection Guide — Quick Decision Matrix
● Beyond Single vs Double — Other Bollard Types You Should Know
● Installation and Maintenance Considerations
● User Feedback — Real-World Perspectives
● How Nanjing Taidun Supports Your Mooring Bollard Needs
● Frequently Asked Questions (FAQ)
When designing a new berth or upgrading an existing terminal, one of the most common questions we hear is: "Should I choose single bollard or double bollard?"
It seems like a simple question. But the answer depends on vessel types, mooring line configurations, tidal ranges, and operational demands.
I have spent years manufacturing OEM mooring bollards and rubber fender systems for global brands. In this guide, I will walk you through the single bollard vs double bollard decision—so you can select the right bollard for your specific application, avoid costly mistakes, and ensure safe, efficient mooring operations.
Before comparing, let's define our terms.
A single bollard consists of one vertical post, typically equipped with one or more horns or studs for securing mooring lines. It is the most basic and widely used form of marine mooring bollard.
Key characteristics:
- Simple, single-post design
- Suitable for smaller vessels or general-purpose mooring
- Often called "pillar bollard" or "single bitt"
- Allows lines to be secured from various angles
A double bollard consists of two vertical posts mounted in line (one in front of the other), creating a twin-column structure. It is designed for heavier vessels and higher mooring loads.
Key characteristics:
- Two-column design (twin bitt)
- Offers greater strength and stability than single bollard
- Sometimes called "twin horn" or "double bitt" bollard
- Allows multiple lines to be secured independently
| Comparison Factor | Single Bollard | Double Bollard |
|---|---|---|
| Load capacity | Lower (sufficient for small to medium vessels) | Higher (handles heavy mooring loads) |
| Mooring line density | Limited (best for 1-2 lines) | High (can handle multiple lines independently) |
| Line release independence | All lines share one post | Each line can be released without affecting others |
| Spring line security | Moderate | Excellent (opposing columns secure spring lines) |
| Space required | Smaller footprint | Slightly larger footprint |
| Cost | Lower initial cost | Higher initial cost |
| Best vessel types | Small cargo, fishing boats, general cargo | Large bulk carriers, container ships, tankers |
| Ideal for spring lines | Acceptable | Superior (greatest strength parallel to berth) |
> *"Double Bitt bollards are useful when high densities of mooring lines are present. The two-column design allows two lines to be secured and independently released without compromising the mooring of an adjacent vessel."*
The most critical factor in the single bollard vs double bollard decision is the mooring load—the force the bollard must withstand.
Mooring forces depend on multiple variables:
- Vessel size and displacement
- Wind and current conditions
- Wave height and tidal variations
- Passing vessel effects
- Mooring line elasticity
- Tidal levels
> *"For large cargo ships, tankers, or container vessels, high-capacity bollards such as tee bollards or double bitt bollards are necessary to handle strong mooring forces."*
| Vessel Type | Typical DWT | Recommended Bollard Type |
|---|---|---|
| Small fishing/pleasure | < 500 tons | Single bollard |
| General cargo | 500 – 10,000 tons | Single or small double |
| Medium bulk carrier | 10,000 – 50,000 tons | Double bitt |
| Large container ship | 50,000 – 100,000 tons | Double bitt |
| VLCC / Cape size | > 100,000 tons | Heavy-duty double bitt |
A single bollard works well when:
- Only 1-2 mooring lines are required
- Vessels are small to medium size
- Mooring operations are straightforward
- The port handles similar vessel types
Limitation: As one boater noted in a discussion, "The line tries to fall off the top of a single bollard, unless it's very thin rope." This means single bollards require careful line securing to prevent slippage.
A double bollard excels when:
- Multiple mooring lines must be secured
- Independent line release is required
- Spring lines are used (the opposing columns excel here)
- Vessels vary significantly in size
> *"The two column design allows two lines to be secured and independently released without having to compromise the mooring of an adjacent vessel. The opposing sloping columns are particularly useful for securing of spring lines as their greatest strength is parallel to the berth."*
Tidal range dramatically affects mooring line angles.
As water level changes, mooring line angles change. Extreme angles increase stress on both the line and the bollard.
| Tidal Condition | Recommended Bollard | Reason |
|---|---|---|
| Small tidal range (< 2m) | Single or double (either works) | Line angles remain moderate |
| Large tidal range (2-6m) | Double bitt or T-head | Better handling of high line angles |
| Extreme tidal range (>6m) | Double bitt with high-angle design | Superior angle accommodation |
> *"T-head and Staghorn bollards can handle higher line load angles than Single Bitt and Kidney shaped bollards. This feature may be of particular importance where very large changes in water level result in significant differences in line angles."*
Single bollards with simple pillar designs are better suited for small tidal ranges, while double bitts offer more flexibility in challenging tidal conditions.
Spring lines run at angles along the vessel, preventing forward/backward movement. They require bollards with specific characteristics.
- Single bollard: Acceptable for light spring line duty, but not optimal.
- Double bollard: Excellent for spring lines—the opposing sloping columns provide greatest strength parallel to the berth.
For terminals where spring lines are critical (container terminals, ferry slips), double bollards are strongly recommended.
| Bollard Type | Base Area | Best For |
|---|---|---|
| Single bollard | Smaller | Space-constrained docks, small berths |
| Double bollard | Slightly larger | Commercial ports with adequate deck space |
Some double bitt designs feature a small base area that is space-saving for small areas, making them viable even in tighter spaces.
Use this table to identify the right bollard for your specific application:
While focusing on single bollard vs double bollard, it's worth understanding other common types for complete context:
> *"Kidney shaped bollards offer an economical solution for installations where securing of mooring lines at high angles is not a concern. This style is not recommended when multiple mooring lines will share one bollard."*
Placement is as important as type selection. Port engineers recommend:
- Spacing: 15–30 meters apart, or roughly 15% of the shortest ship length
- Setback: 0.5–0.8m from the pier edge for general mooring
- Alignment: Coordinate with fender positions
The bollard is only as strong as its foundation. Key anchorage considerations:
- Anchor bolt size, grade, and embedment depth
- Concrete strength and reinforcement bar location
- Whether the bollard is keyed into concrete or surface-mounted
> *"Bollard suppliers are sometimes asked to demonstrate anchor pullout capacity, but this needs to be determined by the wharf's structural engineer, who should be in close communication with the bollard supplier."*
> *"Ductile iron often performs best in marine conditions because it resists corrosion and impact."*
| Frequency | Action |
|---|---|
| Weekly | Quick visual check |
| Quarterly | Inspect bolts, welds, corrosion |
| Annually | Full inspection; touch up coating |
| 5 years | Load testing (recommended for critical applications) |
We asked port operators about their experience with single vs double bollards:
> *"We used single bollards for years at our general cargo terminal. When we started handling larger container ships, we had to retrofit double bitts. The difference in stability is night and day—especially when spring lines are used."*
> — *Terminal Manager, Southeast Asian Port*
> *"Our ferry terminal operates with double bitt bollards exclusively. We need quick line handling and the ability to release lines independently. Single bollards simply couldn't keep up with the pace."*
> — *Operations Director, European Ferry Terminal*
> *"For our small fishing harbor, single bollards are perfect. Simple, cost-effective, and the fishermen know exactly how to use them. Double bitts would be overkill."*
> — *Harbormaster, North American Fishing Port*
At Nanjing Taidun Marine Equipment Engineering Co., Ltd., we manufacture both single and double bollards to international standards, with OEM flexibility for global brands.
Our mooring bollard capabilities include:
| Service | Description |
|---|---|
| Single bollard (50-1000kN) | Standard and custom designs |
| Double bollard (100-2000kN) | Heavy-duty; various configurations |
| T-head and horn designs | Available for specialized applications |
| Material options | Cast steel, ductile iron, stainless steel |
| Surface protection | Hot-dip galvanizing, epoxy coating, marine paint |
| Third-party testing | Load testing; ABS, BV, LR certification available |
We serve brand owners, wholesalers, and production facilities in over 80 countries. When you partner with Taidun, you get factory-direct pricing, custom engineering, and full certification documentation for both single and double mooring bollards.
The single bollard vs double bollard decision comes down to four factors: vessel size and mooring load, line density and configuration, tidal range, and spring line requirements.
- Choose single bollard: Small vessels, simple mooring, low line density, small tidal range
- Choose double bollard: Large vessels, multiple lines, high tidal range, spring line critical
[Contact the Nanjing Taidun Engineering Team] for a free mooring bollard consultation. Send us your vessel specifications and berthing conditions, and we will recommend the optimal bollard type, size, and configuration for your operation.
Q1: What is the main difference between single and double bollards?
A: A single bollard has one vertical post for mooring lines, while a double bollard has two posts. Double bollards offer higher load capacity, independent line release, and better handling of multiple mooring lines.
Q2: When should I choose a double bollard over a single bollard?
A: Choose double bollards for large vessels (container ships, tankers, bulk carriers), high mooring line density, locations with significant tidal range, and where spring lines are critical.
Q3: What is the typical spacing for bollards along a berth?
A: Bollards are typically spaced 15–30 meters apart, or approximately 15% of the shortest ship length expected at the berth.
Q4: What material is best for marine mooring bollards?
A: Ductile iron offers excellent marine corrosion resistance and impact resistance. Cast steel provides higher strength for heavy-duty applications. Both require proper coating for maximum lifespan.
Q5: How often should mooring bollards be inspected?
A: Perform quick visual checks weekly, detailed inspections quarterly, and full annual inspections. Look for loose bolts, cracks in welds, corrosion, and surface wear.
