Bringing an LNG carrier alongside a terminal or floating facility requires certain techniques and equipment for a successful operation, and once in position, advances in technology can make the whole mooring process safer, too
When it comes to manoeuvring large LNG carriers in open water with escort tugs, a major tug operator has stated a preference for a certain type of equipment based on the size of the LNG carrier to be manoeuvred, the location of the terminal, the expected weather and sea conditions and distance from shore. Weight, costs, energy source, controls and line length are also factors considered when selecting deck machinery.
In a video interview at the LNG Shipping & Terminals Conference 2023 in London, Smit Lamnalco global director for LNG business and project development, Andrew Brown, explained the operational advantages of using render-recovery winches to manoeuvre gas carriers at offshore terminals, such as assisting LNG carriers alongside liquefied gas production and export (FLNG) ships and floating storage and regasification units (FSRUs).
He said the performance of drum-based winches is inferior to render/recovery winches in open water when wave heights and sea states have more influence on towline strain. But drum winches are excellent tools where the sea state is not so dynamic.
"When we are manoeuvring an LNG carrier next to an FLNG, we are doing that in open ocean, where we have a variation of dynamics,” said Mr Brown.
These dynamic sea conditions result in the LNG carrier, FLNG or FSRU and the tugs handling the ships moving. “We have to tow the LNG carrier and get it alongside the FLNG in wave heights up to 2.8 m,” he said.
Smit Lamnalco provides marine services around oil and gas terminals, single point moorings and LNG import and export infrastructure. It uses winches and towing lines to keep close control over tanker and gas carrier movements around these terminals.
“If there is a drum and brake winch, that is basically fixed. But when there is much movement, there is a lot of stress on the line that is towing the LNG carrier,” Mr Brown said.
“What we prefer in open ocean is to have some slack in that line. The render-recovery winch anticipates that movement, and we can switch it on and switch it off, which allows the rope to pay out and pay in. It follows the movement of the dynamics of the ocean.
“In open ocean we prefer to have some slack in the line”
“The render-recovery acts like a damper,” he continued. “It takes the strain of the line and that is why we prefer to use render-recovery winches rather than drum and brake winches when we are working offshore.”
Smit Lamnalco’s escort and ship-handling tugs have render-recovery winches on board to improve operational safety and to prevent crew injuries.
“When we have a lot of dynamic movement because of the waves and how the tugs and the LNG carriers are behaving, we use the render-recovery bridge on the line, so we can pay out and pay in, and recover based on the dynamics of the ocean,” said Mr Brown.
“If we are inside a port or a harbour, where we do not have those dynamics of movement, then a drum and brake winch works perfectly well,” he said. Having a render-recovery winch minimises the risk of the towline snapping from the varied movements and dynamics on these vessels.
Another advance in towage is the shift in demand towards electric winches in the past few years, according to Data Hidrolik, which offers hydraulic and electric drive machinery with up to 180 tonnes braking power and 80 tonnes pull.
Following feedback from clients, the Turkish company has developed control and alarm panels according to class requirements, said Data Hidrolik sales and marketing director, Cem Hüroğlu.
“Demand has increased dramatically especially in the last two years, and on our orderbook, the percentage of electric-driven winches increased rapidly,” he explained. “We think this happened because of precise control options on electric systems.” It is also due to owners wanting to reduce the risk of hydraulic oil leaks and the easy access to available electric drives and electronic controls.
“Our starting point was with hydraulic-driven equipment, but we changed to electric-driven equipment production,” said Mr Hüroğlu. “We have standard designs, but we also need to modify our designs according to client requests.”
He said the important factors in selecting winches include pulling force, braking force and drive type.
Data Hidrolik provides deck machinery to the major Turkish tug builders – Sanmar, Med Marine, Uzmar and Navtek – including supplying electric-driven equipment for battery-powered tugs.
“We are working with all these producers and designing our winches and control systems according to their needs,” said Mr Hüroğlu.
These advances in handling towing lines can minimise the risk of the towline snapping from the varied movements and dynamics on these vessels, but the danger does not end there, as once alongside the terminal or floating LNG facility, a snapping mooring line can be potentially fatal to any crew member in the danger zone. There have been various attempts to mitigate the situation, including industry guidelines such as the OCIMF Memorandum Equipment Guidelines and SOLAS guidelines in shaping safety protocols.
One of the latest technological solutions is the Defender Fuse from Samson Ropes, whose engineering manager, Dustin, Heins explained how this technology can mitigate the risk of recoil in mooring scenarios. He noted Defender Fuse has undergone full-scale testing and is a collaborative effort with regulatory bodies such as the American Bureau of Shipping.
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