ABS issued a report focusing on the design aspect of position mooring systems. The Guide also provides criteria, technical requirements, and guidance on the design and analysis of position mooring systems.
A mooring system has to restrict the offset of a floating structure/unit within prescribed limits, and maintain the directionality when the structure’s orientation for safety or operational considerations.
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The criteria for offset and orientation are established either by the owner of the floating structure/unit or directly derived from design requirements including those related to:
- Safety of personnel;
- Stability of the floating structure;
- Serviceability of the floating structure, and intended operations;
- Drilling riser and production riser requirements;
- Access to and clearances with respect to nearby installations;
- Any other special positioning requirement.
Furthermore, a mooring system has to withstand environmental and other forces. In order to ensure the strength of a mooring system, the designs must consider the following:
- Ultimate Limit States (ULS): The mooring system and its components are to be designed to have enough strength to withstand the load from extreme environmental conditions.
- Fatigue Limit States (FLS): The mooring system and its components are to be designed to have enough capacity to withstand the cyclic load because of exposure environments;
- Accidental limit state (ALS): The mooring system and its components are to be designed to have enough capacity to withstand the load from extreme environmental conditions when the mooring system loses any one of the mooring lines, or thrusters for thruster assisted mooring systems.
Finally, calculations of the maximum mooring system loading must consider various relative directions of the wind, wave and current forces.
See further details in the PDF herebelow
