Andrew Stafford - Using Mooring Tension Data
MEG4 (Mooring Equipment Guidelines Issue 4) has highlighted that having access to accurate data on the condition of mooring equipment is key to ensuring the safety and longevity of the mooring equipment on vessels. It took the tragic incident onboard the LNG carrier Zarga to drive change forward when perversely, the LNG tanker fleet is one of the most advanced in terms of being able to monitor and even record rope tension whilst in port.
Most LNG terminals will be equipped with instrumented mooring hooks capable of reading the tension of each of the mooring ropes. In the majority of terminals, this data can be presented to the crew onboard the vessels via a Mooring Load Monitor (MLM) repeater. Although the terminals specify and are in control of the hooks and the ships typically include some sort of inbuilt repeater software interface, there is no common protocol for the transmission of the data itself.
System configurations currently available include:
• Radio – Carry onboard repeater systems
• Ship to Shore Link systems – hardwired data channel via SSL
• Bespoke terminal specific requirements.
There are strict berth requirements at some terminals for visiting LNGCs to be able to connect and read mooring data without there actually having been any publication of the data format. The layout of jetties also varies from berth to berth so there is no standard solution or arrangement that can work for all applications. Solving problems like these have led to the development of novel and innovative solutions, however as the LNG terminal base expands, the variety, complexity and compatibility of such solutions are likely to become increasingly problematic for terminal and vessel operators as well as OEMs.
More complex mooring arrangements, such as those used in floating LNG applications, have compound mooring arrangements which need careful monitoring and even levels of cross-platform control of the mooring hardware to ensure safety during the operation. Dynamic data analysis of these arrangements can be used to further enhance the robustness of the mooring arrangement.
This paper will review the development and deployment of these various applications, options and solutions that can be applied to ensure that as much mooring data as possible can be transmitted reliably and captured during the period alongside. It will highlight the areas of incompatibility that changes in the fleet have caused to legacy infrastructure and will detail the alternate solutions with a pros and cons analysis to be able to keep this important interface operational within the fleet.
The author has been working with LNG ESD systems including the mooring tension repeater interfaces for over 15 years and has been involved in working groups and technical committees of SIGTTO, SGMF and OCIMF.