Wire rope in offshore moorings: Uses, construction, and fatigue

Wire rope is a versatile, high‑performance component across offshore mooring systems and broader marine operations. This article covers  

• Wire rope applications in offshore moorings and marine operations
• Wire rope fabrication and configurations
• Performance, corrosion protection and inspection 

Why wire rope is a versatile choice 

In moorings, it can be used for  

• Motion control and stationkeeping,
• Vessel positioning and line management
• Specialised roles within semitaut mooring configurations 

Beyond moorings, it can be used for other tasks such as guidance, tie down, hold back, lifting, and many more.  

Compared to chain, steel wire ropes have a higher strength to weight ratio, making them easier to install and lighter on the floating structure. 

Wire rope construction and configurations 

Stranded wire rope 

Steel wire ropes are mostly commonly constructed of many thin steel wires wound into strands, which are then wound around a central core into the final wire rope. The most commonly used configuration for this type of wire construction is six strands. The number of strands and wires in each strand (e.g. 6 × 19, 6 × 36, 6 × 61) is governed by required strength, fatigue and bending stiffness requirements for each application.  

During selection consideration, it is important to note that this construction can generate torque as tension increases. 

Spiral-strand and locked-coil 

Wire rope can also be constructed of only individual wires tightly spaced and wound without stranding, known as spiral strand.  

This construction commonly uses a sheath for protection since it is much more susceptible to damage.  

To eliminate torque, the rope construction (spiral strand, half locked and full locked coils) uses layers of wires (or bundles of wires) wound in opposing directions to obtain the torque balanced characteristics. 

Terminations 

Termination connections are available in various sizes to accommodate any size of mooring components. 

Wire rope performance 

Wire rope has a lower fatigue life and is more sensitive to damage and corrosion compared to chain. To sustain performance 

• Corrosion protection: As per DNV-OS-E304, wire rope segments in mooring lines are to be protected against corrosion attacks throughout the design life, either through coating of the strands or sheathing of the rope.
• Regular inspection: visual checks, sheath integrity verification and condition assessments are recommended throughout the design life to ensure the protection is intact and corrosion is within acceptable limits.
• Handling and installation: Use appropriate sheaves, drums, and fairleads to avoid kinks, crushing, and sharp bends that accelerate fatigue. 

All wire ropes and components should be certified and approved for offshore use per project standards and quality assurance requirements, with documentation maintained through installation and operations. 

Intermoor, Acteon’s Moorings and Anchors business line, offers varying sizes and configurations for wire rope. All wire ropes have an independent wire rope core (IWRC) of the highest quality grade and meet all requirements necessary to perform in the offshore industry.