Two Approaches to Mooring: What Sets Them Apart
When designing marine LNG terminals, the choice of mooring system has a profound impact on both installation and environmental footprint. Dolphin mooring is the traditional approach, relying on rigid, fixed structures installed on the seabed. This method demands significant seabed intervention, involving heavy piling and extensive civil works, which can be both costly and disruptive to the marine environment. Vessels are held tightly in place with lines and fenders, minimizing movement to accommodate conventional loading arms.
Spread mooring systems, on the other hand, use multiple anchors positioned around the vessel for stationkeeping. Their lower stiffness allows greater vessel horizontal movement (surge, sway, yaw). When combined with jettyless cargo transfer system, they typically offer higher uptime than dolphin mooring systems. With minimized seabed interaction, spread mooring significantly reduces both the time and environmental impact associated with terminal construction. Furthermore, the spreading mooring system typically utilises standardised and lightweight components, which facilitate a more rapid and minimally intrusive installation process.
Key technical differences:
- Dolphin mooring requires extensive piling and civil works, resulting in a larger environmental footprint.
- Spread mooring minimizes seabed interaction, offering a more sustainable and efficient solution, especially when paired with floating transfer systems like the IQuay C-Class.
Why Motions Matter: Unlocking Operational Flexibility
One of the most overlooked aspects in marine terminal design is how much vessel movement the mooring system allows. In conventional dolphin mooring setups, movement is tightly restricted, as vessels must remain almost perfectly still to keep loading arms aligned and safe. This rigidity can lead to low operational uptime, especially in rough weather or in ports with significant passing ship traffic, where ocean waves and waves generated by passing vessels can cause unwanted movement.
To mitigate these challenges, breakwaters are often constructed to shield terminals from waves. However, building breakwaters is a significant investment and can dramatically increase project costs.
Spread mooring systems, by contrast, are engineered to accommodate larger vessel motions. This flexibility means that gas transfers can continue safely even when weather conditions are less than ideal, and without the need for costly breakwater infrastructure. When combined with floating platforms and jettyless solutions, spread mooring enables higher uptime and reduces the need for expensive interventions.
Key technical points:
- Motion envelope: Spread mooring allows a larger vessel motion envelope without compromising safety or transfer integrity.
- Compatibility: Floating transfer systems like the IQuay C-Class are designed to work with spread mooring, leveraging this flexibility to maximize operational windows.
Risk Management and Operational Assurance
Beyond installation and day-to-day flexibility, the choice of mooring system has significant implications for risk management and the long-term reliability of the terminal. The fixed infrastructure of dolphin mooring can simplify certain emergency scenarios, but it also means that any failure, such as a damaged pile or misaligned loading arm, can halt operations until major repairs are completed. Additionally, the rigid nature of dolphin mooring increases the risk of damage during navigation, especially in busy terminals. This highlights the potential for incidents where both ships and infrastructure are at risk.
Spread mooring, while newer to the LNG sector, introduces a different approach to risk. Its distributed anchoring and allowance for vessel movement mean that forces are shared across multiple points, which can help mitigate the impact of unexpected events such as vessel contact or environmental loads. Spread mooring is normally designed with redundancy, meaning that the system can continue operating safely even if a single component fails, which adds resilience compared to rigid alternatives. Many components in spread mooring systems, such as anchors and chains, are standardised and commercially available. This can simplify maintenance and replacement compared to the more bespoke infrastructure required for dolphin mooring, although practical considerations like mobilisation and site access still play a major role.
Maintenance routines also differ: dolphin mooring requires regular inspection of fixed structures and tensioned lines, while spread mooring systems focus on anchor integrity, buoy condition, and sensor calibration. As digitalisation and remote monitoring become more common, spread mooring’s compatibility with these technologies is increasingly attractive to operators seeking proactive risk management. At ECOnnect, detailed mooring analyses are part of every engineering and study package, ensuring that each solution is tailored to site-specific conditions and safety requirements.
Real-World Example: Altamira FLNG 1
At Altamira FLNG 1, a spread-moored FSU was chosen because it is the most efficient station-keeping solution for a jettyless terminal in shallow, moderate waters. The site allows conventional catenary or semi-taut lines, avoiding the heavy civil works and permitting complexity required for dolphin mooring. Spread mooring also provides stable heading and low vessel excursions, which is essential for maintaining predictable geometry between the FSU, the processing units, the IQuay, and visiting LNG carriers. This reliability is difficult to achieve with dolphin systems, which fix vessels in a berthing arrangement and limit operational flexibility. The choice supports the project’s low-infrastructure, fast-deployment philosophy.
In short, Altamira shows that in suitable water depths, spread mooring delivers a simpler, faster, and more adaptable alternative to dolphin mooring for offshore LNG operations.
Why Spread Mooring Is Gaining Ground
Spread mooring has clear advantages, yet adoption in the LNG industry has historically been limited. The main reason is that spread mooring was not compatible with conventional loading solutions, which required vessels to be in designed mooring position accurately. As a result, the industry relied on dolphin mooring and other rigid infrastructure for decades, prioritising proven reliability and safety.
The turning point has come with the development of floating transfer systems. In addition to enabling spread mooring, these innovations make LNG terminals possible in locations where conventional jetties would be impractical or prohibitively expensive. By removing the need for massive civil works and rigid infrastructure, jettyless solutions open new markets and allow safe operations in harsh environments. Lead time is another critical factor. Dolphin mooring systems often require months of piling and bespoke construction, while spread mooring uses standardised components and involves far less geotechnical work, significantly reducing installation time.
The supplier landscape is also evolving. As more projects implement spread mooring, standardised solutions are becoming available, reducing costs and simplifying deployment.
Case in point:
Recent jettyless LNG transfer projects show that spread mooring delivers improved flexibility, easier vessel handling, and robust safety systems without the environmental impact of traditional dolphin mooring.
Looking Ahead: Spread Mooring in Current Projects
Beyond Altamira, spread mooring is under active consideration for several of our current engineering studies and project proposals. In these cases, its rapid deployment, reduced seabed intervention, and compatibility with floating transfer systems make it an attractive option for sites where traditional infrastructure would be impractical or cost prohibitive. While specific project details remain confidential, the growing interest reflects a broader industry shift toward more flexible and sustainable terminal solutions.
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