Subsea Mooring Line Adjustment Using Chain Locking and Tension Transfer
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Solution Overview
Problem
Mooring systems, particularly those using polyester ropes in deep to ultradeep waters, face line length variations due to creep over time, necessitating adjustments within the design envelope without exceeding practical tension limits during installation.
Innovation Solution
A subsea line length and tension adjusting device that connects and adjusts the mooring line sections using a locking element and temporary pulling means, allowing for precise lengthening or shortening by transferring tension through a chain segment with a hinge mechanism and stoppers to manage friction and loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If high tension is applied during installation to mitigate creep, then line length stability is improved, but installation vessel capacity requirements and operational risk increase
Solution Approach 1:
The device applies preliminary stretching action to the polyester rope section during installation to pre-mitigate creep effects. The stretching mechanism gradually tensions the rope to a controlled extent before final deployment, achieving creep mitigation without requiring excessive tension that would exceed vessel capacity or safety limits.
2Manufacturing precision
If line length adjustment is performed by opening the mooring line, then adjustment precision is improved, but operational complexity and time increase
Solution Approach 1:
The adjusting device is nested within the existing mooring line structure, with the stretching mechanism integrated into the chain-polyester rope transition assembly. The device includes nested components such as the stretching mechanism housed within the connector assembly, allowing adjustment without external intervention or line opening.
Solution Approach 2:
The device enables self-adjustment of line length through automated or remotely-controlled stretching mechanisms. The system can perform length adjustments autonomously by activating the stretching mechanism to tension the polyester rope section to the desired length, eliminating the need for manual line opening and reassembly operations.
3Reliability
If chain segment friction is increased to prevent slippage, then connection reliability is improved, but tension transfer efficiency deteriorates
Solution Approach 1:
The device applies local quality differentiation by providing high friction only at critical contact points where slippage prevention is essential (such as between the chain links and the stretching mechanism gripping surfaces), while maintaining low friction surfaces in tension transfer pathways. This selective friction application ensures connection reliability without significant energy loss in the overall tension transfer system.
Data Source
AI summary
A mooring line length adjusting device and method is disclosed. The device is arranged for connecting lower and upper mooring line section to its respective ends and for adjusting the total length of the mooring line. The upper section of the mooring line includes a chain segment at its end connected to the device. The device includes a locking element to lock the chain segment to itself. A connecting structure for a temporary pulling mechanism to pull the device in a direction to transfer tension from the upper mooring line section to the temporary pulling mechanism is a part of the device. The method discloses steps and details how to use the device.