Inline Tensioner for Polyester Mooring Line Stretch Removal
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Solution Overview
Problem
Floating structures and vessels face challenges with mooring line stretch due to visco-elastic elongation of polyester lines, leading to vessel movement outside acceptable excursion circles, and require costly re-tensioning operations, especially when support vessels are not available.
Innovation Solution
A method and arrangement that utilize an inline tensioner system to impose a pre-tension force on the mooring line, followed by a transverse force to remove stretch, allowing for efficient tensioning and re-tensioning without the need for on-deck equipment, using a midwater coupling and second tensioning line to amplify tensioning force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional chain tensioning equipment is used on deck for pre-tensioning, then the mooring line can be tensioned during installation, but the equipment seizes or corrodes over time and requires refurbishment
Solution Approach 1:
The patent removes the tensioning equipment from the floating structure entirely, extracting only the essential function of tensioning. The inline tensioner system is deployed in the water column rather than being mounted on deck, eliminating corrosion and seizure issues while maintaining the ability to tension and re-tension mooring lines throughout their service life.
Solution Approach 2:
The patent introduces an intermediary inline tensioner system that operates in the water column between the anchor and the floating structure. This mediator performs the tensioning function without being permanently attached to the floating structure, avoiding the reliability issues of on-deck equipment while maintaining full tensioning capability.
2Reliability
If polyester mooring line is tensioned to required levels, then the vessel is moored at correct position, but the line elongates over time due to visco-elastic stretch causing vessel to move outside acceptable excursion circle
Solution Approach 1:
The patent applies preliminary action by performing stretch removal during the initial installation phase using the inline tensioner system. The system tensions the polyester line to high levels (exceeding 40% of minimum break load) and maintains this tension to remove visco-elastic elongation before the mooring enters service, preventing future position drift without requiring excessive ongoing tension.
Solution Approach 2:
The patent changes the tension parameter dynamically during installation, applying high tension levels temporarily to remove stretch, then adjusting to the optimal operating tension level. This parameter change approach eliminates the need to maintain excessively high continuous tension, reducing loads on the mooring system while ensuring position stability.
3Reliability
If re-tensioning is performed after installation, then the mooring line tension can be restored, but costly support vessels are required and equipment must be available
Solution Approach 1:
The inline tensioner system is designed to be self-service capable, allowing re-tensioning operations to be performed by the same system that performed initial installation. The system can be deployed and retrieved as needed, enabling the mooring to service itself without requiring external support vessels or specialized equipment, significantly reducing re-tensioning costs and time.
4Reliability
If high pre-tension level is applied during installation, then stretch removal is effective, but the tensioning force required is very high
Solution Approach 1:
The patent applies another dimension by using a pulley system that redirects the tensioning force through a geometric arrangement. The inline tensioner uses a pulley positioned perpendicular to the mooring line, creating a mechanical advantage that multiplies the effective tensioning force. This dimensional change in force application allows high pre-tension levels to be achieved with moderate pulling force, making stretch removal effective without requiring excessive tensioning capacity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly reduces the need for costly re-tensioning operations by removing stretch during the initial installation phase, enabling effective mooring with smaller vessels and minimizing weight and overtightening issues.
Implementation Method 1
When a new polyester mooring line is tensioned, it tends to elongate over time due to visco-elastic stretch and permanent unrecoverable stretch.
Implementation Method 2
imposing a substantially transverse force on the part of the mooring line extending between the anchor and the floating structure in order to remove stretch in the mooring line
Data Source
AI summary
The invention relates to a mooring tensioning arrangement for a floating structure or a vessel (11), comprising -a mooring line (3, 5, 7) having a first mooring part (3) and a second mooring part (5, 7), divided by a midwater coupling (4, 40, 400, 111), said at least a portion of the mooring line (3, 5, 7) is made of synthetic material, -said mooring line (3, 5, 7) is extending between an anchor (2) arranged on the seabed and a pulling unit (9, 10, 42) arranged separate from the floating structure or vessel (11), said mooring line (3, 5, 7) is extending at least via a fairlead pulley or a chain wheel (8, 80) arranged on the floating structure (11) between the anchor and the pulling unit (9, 10, 42) when the mooring line (3, 5, 7) being pre-tensioned, -a chain stopper (6, 60) being arranged in connection with the mooring line (3, 5, 7) between the anchor (2) and the floating vessel or structure (11) for tensioning the part of the mooring line (3, 5, 7) situated between the floating structure (11) and the anchor (2) at a pretension level. The mooring tensioning arrangement further comprising a second tensioning line (100) configured to be attached in one end to the midwater coupling (4, 40, 400) and in the other end coupled to the pulling unit (9,10, 42) when said mooring line (3, 5, 7) being re-tensioned, said midwater coupling (4, 40, 400) and the pulling unit (9, 10, 42) being arranged relative each other such that the tensioning line (100) is configured to impose a lateral force on the part of the mooring line (3, 5, 7) arranged between the anchor (2) and the floating structure (11) for removing stretch in the mooring line (3, 5, 7). The invention also relates to a method tor tensioning the mooring tensioning arrangement.