Sanmar completes the world’s first LNG tug
Early in October, tug builders Sanmar held a massive event to name the world’s first LNG fuelled tug, Borgoy, built for Norwegian tug owners Bukser og Bergings AS (B&B).
Borgoy and sister ship Bokn, nearing completion, were introduced to a large gathering of visitors from the towage industry and maritime press at Sanmar’s Tuzla facility in Turkey. The introduction of this entirely new breed of gas powered tugs, was part of a ‘Five tugs ceremony’ during which three other new vessels, also under construction for B&B, were revealed, further details of which follow later in this feature.
Borgoy and Bokn were designed in-house by B&B with the assistance of Marine Design AS in Norway and further development by Sanmar. They are the first tugs in the world to be fuelled by the environmentally friendly liquefied natural gas (LNG) to eliminate sulphur emissions, bring particulate matter emissions down close to zero and reduce the discharge of CO2 and NOx by 26% and 80-90% respectively. On completion both tugs will enter service at the Kårstø gas terminal in Norway, under contract to the Norwegian state oil company Statoil.
The ASD tugs are built to DNV Class; 1A1, EO,Gas-fuelled,Oilrec,FiFi1, Escort (100,10). As indicated, these are escort tugs built to an advanced design capable of generating steering forces in escort mode of 100 tonnes at 10 knots. A static bollard pull of 70 tonnes is specified, along with a free running speed of 13.5 knots. For ancillary tasks where close quarter manoeuvrability is required a 333kw Schottel bow thruster is installed. The tugs are equipped for fire fighting and oil recovery duties.
Borgoy and its sister have length of 35m, a beam of 15m and draft of 5.5m. In order to deliver a high escort capability the tugs have a unique hullform that includes a massive skeg, of hydrofoil section in planview, extending from just below the bow for almost two thirds the length of the hull. This unusually large skeg is designed to produce very high ‘lifting forces’ when towing in the indirect mode.
Each tug is powered by two Rolls-Royce Bergen C26:33L6PG, spark ignition, lean-burn engines fuelled entirely by LNG, and developing a combined output of 3,410kW (approximately 4,574 bhp) at 1,000 rpm. Each engine is coupled to a Rolls-Royce US35 fully azimuthing propulsion unit of the latest type, incorporating propellers of 3,000mm diameter. The Bergen gas fuelled engines can operate on low load without any restriction, have a very quick and stepless ramp-up time from 0 to 100% load, and are easy to service and maintain. The lean burn principle delivers high efficiency coupled with reduced exhaust emissions and low specific energy consumption.
Rolls-Royce Acon control and monitoring equipment is installed for the gas system, which comprises one AGA Cryo LNG tank and two cold boxes. The LNG system is designed by AGA Cryo and integrated with the Rolls-Royce propulsion system. This single tank LNG system has full gas redundancy approved by NMD (Norwegian Maritime Directorate) ie, no diesel back up is required. The fuel system is designed for weekly bunkering to be carried out by the tug crew and take approximately 45 minutes.
The systems have had to meet the International Code of Safety for Gas Fuelled ships and the DNV Classifcation Society rules. These involve such requirements as independent engine room spaces with ventilation of 30 air changes per hour, gas detection, automatic shutdown of the gas supply and disconnection of electrical equipment, excess flow shutdown, and ventilated double (sheathed) piping. Special knowledge was required for the installation of the Aga Cryro AB 80m3 capacity double-walled tank, cold boxes and gas heating systems. The prominent vent pipes mounted forward of the towing winch are a feature of the LNG propulsion system.
Electrical power aboard these unique vessels is supplied by a pair of Nordhavn auxiliary generators, powered by Scania diesel engines rated at 300kVA, 240kW, 400 volts 50Hz.
A hydraulic system serving the towing winch, bow thruster and deck crane is powered by pumps driven by the main engines. Also driven by the main engines are two Jason fire pumps capable of supplying the fire fighting system at 2,400m3/hour
The tugs are equipped with a towing winch on the foredeck designed for escort work and capable of precise control of towline forces and length.
Accommodation is provided for up to six persons in two single and two double berth cabins as well as a mess room and galley, all to North European standards of comfort and quality. Care has been taken to reduce sound levels throughout the accommodation areas and at 85% engine load, readings of 65dB have been recorded.
Ali Gurun, project director at Sanmar Shipyard said: "Sanmar Shipyard is very proud to be a part of this ground breaking gas fuelled technology. The project has required not only technical knowledge but also great skills in project management and finding flexible solutions, involving both competence and team work. Sanmar is very pleased to be a part of the team with Rolls-Royce and Bukser og Berging. We are receiving a high level of inquiries from all around the world and we expect to build a number of new LNG fuelled vessels in the future."
At the time of writing Borgøy was due to start on a comprehensive programme of sea trials prior to its delivery voyage to Norway under its own power. Both tugs are expected to be in service at Kårstø early in the New Year.
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