A recent news article published in the Riviera states that LNG bunkering has to pay attention to mooring line inclination.
Need for special requirements and care
Experts agree that special requirements and care are required when it comes to mooring LNG carriers alongside FSRUs and LNG bunkering vessels.
How do mooring requirements differ between LNG carriers, FSRUs and LNG bunkering? In Riviera Maritime Media’s webinar Mooring systems for LNG carriers and FSRUs: design, construction and safety, experts passed on the knowledge of what operators need to know when it comes to mooring equipment and rope design, regulatory guidelines, safety and training.
The webinar was sponsored by Dyneema (DSM Protective Materials) and Whitehall Manufacturing Corp.
A team of experts providing advice
The group of experts providing advice comprised Bernhard Schulte Shipmanagement (Deutschland) senior marine superintendent Manish Tyagi, DSM Protective Materials technical and business development manager marine and offshore EMEA Jac Spijkers, and Whitehill Manufacturing Corp director of research and development Mark Huntley.
Mooring LNG carriers alongside jetties and mooring LNG carriers alongside semi-permanent moored vessels such as FSRUs are two very different processes. This is something operators and shipowners need to address, noted Mr Tyagi of BSM, which manages an LNG bunkering operation. The semi-permanent moorings of an FSRU have distinct characteristics. “Such a mooring is susceptible to the creep, which is a function of time, temperature and load,” he said.
“The correct fibre you have to choose as an operator, is one to reduce or eliminate the creep.”
He added it is also important to have the correct protection at the permanent part of the mooring, including protection where the mooring rope passes through the chock.
This protective sock should be long enough that it will not need any adjustment due to movement over time, preventing placing a work team in a dangerous area to make adjustments to the sock.
Turning to the challenge of mooring LNG bunkering vessels alongside the growing fleet of LNG dual-fuel vessels, he noted this includes a wide ranger of vessels, from container ships to VLCCs. The dominant mooring characteristic is the large freeboard of these vessels, producing extreme height differences between the large-scale tanker and the small-scale LNG bunkering vessel. He warned it is extremely important, and good practice, to calculate the effectiveness of the mooring line between the large-scale and small-scale vessels.
“This information should be shared among the small-scale and the large-scale, the people who are involved, so they understand the consequences if something goes wrong,” he advised.
While this should be the case, it was revealed in a webinar poll that more than half (54%) do not calculate the effectiveness of the line’s inclination greater than 25°.
Mr Spijkers followed up the theme with his insight and learnings gained during visiting or inspecting various vessels.
“It is only a very small portion that are due to equipment failures or hardware failure that is leading to incidents or accidents,” he said.
“ Almost two thirds of all rope incidents happen during the berthing operation.”
His preference is that mooring procedures are constantly reviewed and challenged, having noted that where a vessel runs regulary to the same port, there is a tendency for common practice to replace safe practice, and sloppy handling of the berthing operation can creep in.
One solution is regular mooring
One solution is regular mooring training of all the crews rotated on a vessel and crew training in mooring rope inspection.
Referring the handling of synthetic ropes (DSM Protective Materials is the producer of the well-known Dyneema material brand), he said to avoid using hardware that had already been used for steel wire. Hardware should be as smooth as possible and rust-free to reduce the risk of damage to synthetic ropes.
Taking up the challenges of safe mooring in the LNG environment was Mr Huntley, who pointed out another problem area, the wet zone around the chock. The testing of the mooring rope should take account of the impact of the wet zone. He added that the mechanisms behind rope failure can be classed as internal or external. Internal failure is rare, accounting for only 5% of failures. Abrasion accounts for 95% and to make inspection easier, Whitehall has a red tape set in the rope construction.
“We call it the depth indicator,” he said. “We know that if you are in the middle of a mooring operation, you are forced to make a decision on the deck, in real time, and this is a simple inspection aid,” he said. An exposed red tape might require repair but if the damage is beyond the tape depth, the rope is at 90% or less strength. “In that case, you need to remove that damage section, “ he said.
Mr Huntley’s view point
Mr Huntley added that Whitehall has adapted a technique it has ben using in the mining sector to scan ropes for internal damage. A mobile cart is placed on deck and scans the rope on the ship, producing a chart of data spikes. “It’s like an ECG for your rope,” he said.
The accumulation of data over time reveals the wear zones and where a vessel is on a regular voyage, these can be traced back to particular ports and even particular chocks. “The key is, over time, to be able to track those where zones correlate with rope strength data and use this as an objective decision maker for rope retirement,” he said.
Mr Huntley’s main takeaway was that mooring rope inspection should not be a biennial event with the manufacturer on board, but a continual operation with go or no go inspection which depth gauge and scanning can help.
In his takeaway, Mr Spijkers noted there was concern over mooring line tension fatigue and abrasion fatigue and as a fibre manufacturer, the industry must make products safer and more reliable. He included mooring line failure prediction as a key takeaway, too.
Mr Tyagi spoke as an end user and operator and said, “My takeaway is that I would like to familiarise myself with my mooring arrangement and the limitations of my morning arrangement,” he concluded, “The final goal is no injuries, no damages, nothing.”
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