Anchor Line Tensioning via Segmented Chain and Deck-Mounted Tensioner
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Solution Overview
Problem
Existing anchor line installation methods for floating offshore structures face challenges such as difficult handling and storage of long pendants, complex underwater connection procedures, and risk of malfunction due to sand or stone ingress into tensioner devices, as well as inefficient tensioning control with low-powered anchor handling vessels.
Innovation Solution
The method involves lifting the free end of the mooring line onto a deck, connecting a chain tensioner with a short tensioning chain part and a long installation chain part, and using a lifting cable to exert tension from the anchor handling vessel, avoiding seabed contact and allowing for diverless inspection and controlled tensioning, with the option to use synthetic ropes for deep water applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the pendant is made relatively long to reach the seabed anchor line, then the anchor line can be connected to the floating structure, but the handling and storage of the pendant becomes difficult
Solution Approach 1:
The working chain is divided into two distinct segments: a relatively short tensioning chain part and a relatively long installation chain part. This segmentation allows the long installation chain part to reach the seabed while the short tensioning chain part remains manageable on the vessel deck for tensioning operations.
2Ease of manufacture
If the connection between chain tensioner and pendant is made below water level, then the connection can be established, but control over the connection procedure becomes difficult and underwater inspection is required
Solution Approach 1:
The connection procedure is moved from the underwater dimension to the aerial dimension by performing the connection between the chain tensioner and pendant on the vessel deck above water level, enabling visual inspection and easier control while maintaining the capability to establish the connection.
3Ease of operation
If the chain tensioner device is placed on the seabed, then the anchor line can be tensioned, but sand or stones may ingress into the device causing malfunction
Solution Approach 1:
The chain tensioner device is extracted from the seabed environment and relocated to the vessel deck above water level. This removes the device from the harmful seabed environment where sand and stones could cause malfunction, while the device still performs its tensioning function on the anchor line.
4Power
If vessels with low-powered engines are used for tensioning, then operational costs are reduced, but control over the tensioning process becomes inefficient
Solution Approach 1:
The chain is segmented into a short tensioning chain part and a long installation chain part, allowing the tensioning force to be applied at the vessel deck level where leverage and mechanical advantage can be maximized. This enables low-powered vessels to effectively control the tensioning process.
Solution Approach 2:
The chain tensioner device acts as an intermediary mechanism between the vessel's pulling wire and the anchor line. It provides mechanical advantage and force multiplication, enabling vessels with low-powered engines to exert sufficient tensioning force on the anchor line.
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
This method facilitates easy handling and monitoring of the pendant, reduces the risk of tensioner malfunction, and enables controlled tensioning using vessels with low-powered engines, while maintaining optimal anchoring force direction and reducing fatigue on anchor connections.
Implementation Method 1
Exerting an upward tensioning force on the tensioning chain part via the lifting cable
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
This invention relates to an anchor line installation method for mooring an offshore structure (1) to a mooring line comprising the steps of: providing a mooring line (11), with one end connected to the sea bed and comprising at a free end (15) a connector member, lifting the free end (15) onto a deck of an anchor line handling vessel (12), connecting on the anchor line handling vessel (12) a chain tensioner (17) with a connection side to the connector member, providing a working chain (20) into the entry side of the chain tensioner (17), the working chain (20) having a relatively short tensioning chain part (28) and a relatively long installation chain part (21), holding a free end of the installation chain part (21) connected to the anchor line handling vessel (12) while lowering the chain tensioner (17) below water level (46), picking up a free end of a pendant (32) attached on one end to the offshore structure (1) that is to be moored, and attaching the free end of the pendant (32) to the free end of the installation chain part (21) in an interconnect position on the anchor line handling vessel (12) and, placing the interconnect position overboard from the anchor handling vessel (12), connecting a lifting cable of a lifting device on the anchor line handling vessel (12) to the tensioning chain part (28) below water level (46), and exerting an upward tensioning force on the tensioning chain part (28) via the lifting cable.