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NYK adopts LNG fuel for latest tug

Ship & Boat International: November/December 2015

Opening a new chapter in the Japanese towage sector, the country’s first LNG-fuelled tug was brought into service during September 2015 by Wing Maritime Service Corporation, part of the NYK Group.

The 37.2m, 272gt Sakigake has been assigned to duties mainly in the ports of Yokohama and Kawasaki. Positive experience with the vessel will no doubt help foster the wider adoption in Japan of LNG as a more environmentally compatible marine fuel.

Employing a twin-engine, steerable Z-peller propulsion system, and offering bollard pull ratings of 55tonnes ahead and 50tonnes astern, the vessel ranks among the most powerful in the Wing Maritime fleet. She was constructed at the Oppama premises of Keihin Dock Co, a tugbuilding specialist within the NYK Group.

The small size and restricted space availability in tugs and the nature of the operating profile, characterised by large variations in power demand, create particular challenges in developing competitive LNG-fuelled designs.

The Keihin-built Sakigake blends a new level of environmental compatibility with the same hull form and steering and ship-handling performance of the latest diesel tugs. To that end, the yard worked closely with Niigata Power Systems, designer and manufacturer of the dual-fuel engines and propulsion equipment, and with Osaka-based Air Water Plant & Engineering, which was responsible for the LNG fuel system.

Gas mode option
The project provided Niigata with the opening contract for its 28AHX-DF dual-fuel, medium-speed engine design, two of which power Sakigake.

The new addition to the Niigata portfolio is targeted primarily at tugs and offshore service vessels and tailored to proprietary Z-peller configurations. Offered in six-cylinder format, the engine has a nominal maximum continuous rating (MCR) of 1,920kW at 800rpm. However, the application for Sakigake was specified at 1,618kW, running at 750rpm, such that the twin-engine installation denotes an overall power concentration of 3,236kW.

While affording the flexibility to burn marine diesel oil, operation in gas mode achieves a considerable reduction in atmospheric pollutants, to the extent of some 75% less NOx, 30% lower CO2 and a virtual elimination of SOx emissions.

Technologies used in the new dual-fuel engine were developed with the support of Japan’s Ministry of Land, Infrastructure, Transportation & Tourism(MLIT), and were also backed by ClassNK as part of the classification society’s ‘Joint R&D for Industry Program’. 

Acceleration response
The AHX-DF design allows seamless switchover between gas and diesel at any time, from start-up to 100% engine load.

Moreover, a feature that is especially salient to tugs and offshore support vessels is the acceleration response in gas mode, said to be comparable with that of a diesel engine. In addition, stable operation is assured during rapid load increases in gas mode, a characteristic which reflects Niigata’s know-how and experience with gas engines for the stationary power plant market.

An LNG fuel supply contract has been entered into with Tokyo Gas Co, whereby bunkering of the tug is accomplished via flexible hose from a road tanker at Yokohama.

Wing Maritime had put down an earlier marker for environmentally friendly tug design through the 2013 delivery of Tsubasa, Japan’s first tug to be equipped with a hybrid propulsion system, supplied by Niigata. Like the new Sakigake, Tsubasa was built at Oppama by Keihin Dock.

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