Accidental Limit State (ALS) events in floating offshore wind turbine (FOWT) mooring systems can result in severe fatigue damage, high recovery costs, and major lifecycle expenses. TFI Marine’s research introduces SeaSprings as a robust solution to mitigate these challenges.

Scope of Work:

• • Investigation of existing 6-line catenary, semi-taut and taut mooring systems

• • Investigation of SeaSpring enabled 3-line catenary, semi-taut and taut mooring systems

• • Full ULS (Peak Load), FLS (Fatigue) and ALS (Accidental Limit State) analysis of all 6 systems

• • Each mooring system was optimised to meet ULS, FLS and ALS requirements

• • For ALS platform excursion, remaining line load analysis and remaining line fatigue analysis were all completed

• • Full CAPEX and T&I cost evaluation, as well as ALS recovery cost evaluation

Key ALS Challenges in FOWT Mooring Systems:

• • High Fatigue Loads in ALS: In an ALS scenario 6 line system had substantially higher maximum loads on remaining mooring lines resulting in substantial fatigue damage

• • Cost and Complexity: While ALS recovery costs were slightly higher for the 3-line systems, with fewer lines, these were lower over a project life (assuming O&G mooring line failure rates)

SeaSpring Technology – A 3-Line Solution:

SeaSprings enabled 3-line catenary, semi-taut, and taut systems to match the performance of conventional 6-line setups in terms of ULS and FLS.

In ALS scenarios, 3-line systems showed significantly reduced fatigue damage compared to 6-line systems.

ALS recovery costs for 3-line systems were slightly higher per event, but overall lifecycle and installation costs were significantly lower.

Case Study Insights:

Total cost savings of up to $108-142M per 500MW observed when switching from 6-line to 3-line systems.

This analysis demonstrates that substantial reductions in LCOE are achievable.

This paper highlights SeaSpring as a transformative technology that enables simpler, lighter, and more cost-effective mooring solutions for FOWTs – enhancing safety and reducing lifetime costs.