Mooring floating LNG for tomorrow

BP’s Greater Tortue Ahmeyim FLNG offshore Mauritania and Senegal is anchored behind a man-made breakwater. Its system includes 26 mooring lines made of synthetic rope and aramid fibre, tensioned to maintain berth alignment within a 0.3-metre tolerance. Tugs assist with mooring and heading control, reducing reliance on built-in thrusters.

Nigerian newcomer UTM Offshore, partnering with NNPC, plans a turret-moored FLNG at the Yoho field. The internal turret design prioritises proven systems and rotational flexibility. Flexible risers connect to a nearby production platform, reducing subsea complexity.

In Gabon, Perenco’s Cap Lopez FLNG will utilise existing jetty infrastructure at the old oil terminal. A side-by-side offloading system will link the floating liquefaction barge with a converted LNG carrier used as an FSU. Fatigue life for jetty hooks and loading arms remains a key consideration despite mild estuary weather.

In Europe, floating LNG is focused on regasification. The Independence FSRU at Klaipėda, Lithuania, typifies Baltic strategies, permanently berthed at a fixed jetty using quick-release hooks and marine fenders. Toscana FSRU is tethered offshore via a turret-type connection to a fixed subsea riser. A floating pipeline segment and a subsea anchoring spread allow permanent offshore station-keeping, with tugs assisting LNG carriers during side-by-side transfers.

Fatigue management across platforms is increasingly central to long-term operability. In deepwater locations fatigue mitigation is handled through riser configurations: lazy-wave designs, bend stiffeners, and HIPPS systems reduce curvature and stress. For mooring lines, polyester rope segments replace heavy steel to dampen cyclic loads and permit greater elasticity.

Shell’s Prelude highlighted the need for continuous fatigue monitoring after a mooring line failure in 2018, leading to fairlead redesigns and material changes. Load cells and tension monitoring are now integrated. As a Prelude engineer observed: “Mooring failures are rare but not impossible. Engineering redundancy must be matched by operational vigilance.”

Similarly, BP’s Tortue installation employs nylon dampers within synthetic mooring lines, acting as shock absorbers. Aramid is preferred over polyester for the line core to achieve lower creep under load and enhanced fatigue life. Class societies including DNV and ABS now require full-scale fatigue testing of mooring elements.

One compelling design evolution is the move towards hybrid station-keeping. Thruster-assisted mooring, used by Shell and planned by Delfin, allows vessels to orient optimally during offloading, reducing broadside wave impact. Positional mooring (POSMOOR) manages mooring tension actively with controlled thrust.

Dual-vessel configurations such as Eni’s Congo FLNG and FSU pairing challenge traditional LNG terminal assumptions. Operating independently moored but functionally coupled, this setup offers modularity and flexibility. LNG transfer between vessels uses floating cryogenic hoses, designed to withstand fatigue and motion stresses.

Disconnectable turrets, borrowed from the FPSO sector, remain under study for Gulf of Mexico installations. The turret buoy remains moored while the vessel departs during extreme weather, central to Delfin’s risk management approach.

Classification societies are shaping mooring technology expectations. DNV’s OS-E301 mandates full fatigue life assessments including out-of-plane mooring chain bending. ABS updates FLNG-specific guidelines covering turret fatigue, riser insulation, and swivel seal longevity.

Regional regulators are asserting influence. Australia’s NOPSEMA investigations into Prelude’s 2018 mooring incident informed retrofits. In the US, MARAD requires hurricane contingency plans for floating deepwater ports, impacting design choices such as disconnectable moorings.

As the sector expands through 2030, technical diversity in mooring systems will continue. Turret moorings will dominate in harsh environments, but hybrid systems, disconnectable units, and split mooring configurations are demonstrating increasing value. With advances in fatigue monitoring, riser stress reduction, and regulatory guidance, mooring has emerged not just as an enabler, but as a core determinant of floating LNG’s long-term viability.