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    Viking Energy - first supply ship to burn LNG

    Vessel & ROV News // May 23, 2003
    Norwegian shipbuilding group Kleven Maritime has provided more details about the Viking Energy, the first platform supply vessel to be fuelled with liquefied natural gas, which it built for shipowner Eidesvik.

    Said the yard: "Viking Energy is the realisation of the vision of the ship owner Eidesvik AS that gas fuelled support vessels could provide a useful contribution to reducing exhaust emissions. Both this vessel and a sister ship to be owned and operated by Simon Møkster Shipping AS will work on a ten-year charter for Statoil. They will help Statoil to reduce both carbon dioxide and nitrogen oxide emissions across its range of activities, aiding Norway's commitment to the Kyoto agreement."

    Kleven Verft in Ulsteinvik, Norway, part of the Kleven Maritime Group with long experience in constructing offshore service vessels, won the contract to build Viking Energy as its Yard No. 303 to the VS 4403 design from Vik-Sandvik.

    As an important part of the quest for low emissions, the design incorporates the latest thinking in low resistance hull form to reduce the propulsion power needed for the required service speed and carrying capacity, and uses efficient azimuth thrusterswith contra-rotating propellers for main propulsion.

    Apart from its unique propulsion system, Viking Energy is a conventional, large supply vessel, 94m long by 20.4m beam, having a deadweight of 6,013 tonnes at the summer draft of 7.9m and dynamic positioning to IMO DP2.

    Eidesvik has had the vessel built to a very high standard, both technically and in terms of living conditions for the crew, with DnV Clean and COMF-V(3) notation. On sea trials the noise and vibration levels under both transit and manoeuvring conditionswere very low.

    Four main generator sets each rated at 2,010kW supply electric power for propulsion and all services. ABB was responsible for the electrical system.

    The prime movers for the generator sets are Wartsila 6L32DF dual fuel engines, designed to burn gas or oil in any proportion. For minimum emissions LNG is used, but should the ship move away from an area where gas can be bunkered, the engines can run ondiesel fuel, and the 116kW Caterpillar powered emergency genset also uses diesel oil.

    LNG is contained in a giant thermos flask in the middle of the vessel, well protected. The tank is a horizontal cylinder with domed ends, fabricated from 304 grade stainless steel. It comprises an inner and an outer chamber, with a gap of 300mm between the two maintained under a high vacuum to insulate the LNG at -162C from the surroundings. Tank volume is 234m3, giving an effective fuel capacity of 220m3 when filled to the allowable limit. The tank in turn is fitted in a compartment with A60 fire insulation.

    Safety precautions are extensive. All gas lines and valves are enclosed in ventilated sheaths, with alarm sensors to give warning of leakage, and all areas where gas could collect are monitored.

    Before use, the liquid gas has to be vaporised, and supplied to the engines at about 20C and 5 bar pressure. This is carried out by means of a hot water vaporiser unit attached to the gas cylinder. Two coils are fed with hot water from the ship's system;one rated at 390kW vaporises the fuel gas to supply up to 600m3/h of free gas, the other smaller unit boils enough LNG to maintain pressure in the tank.

    A bunkering connection is located on the starboard side of the ship, its enclosure inerted with nitrogen for safety. Bunkering of gas will normally occupy three hours once a week, of which actual LNG transfer takes about two hours. Cryo AB was responsible for the ship's complete LNG system up to the connections to the main engines.

    Viking Energy is able to transport all the usual supplies. Liquid mud is carried in eight tanks flanking the LNG system amidships.

    Aft of this are a further eight pressurisable tanks totalling 400m3 for dry bulk. 1,300m3 of fuel can be carried, together with 2,000m3 of ballast/drillwater, 1,100m3 of potable water and 200m3 of methanol or special products. The cargo deck is sheathedin wood and has an area of 1,030m2.

    High plated bulwarks enclose it and right aft at either side of the vessel above the rail height are manifold stations for supply transfer. Two Hydramarine deck cranes are mounted at the aft end of the superstructure, while the Norsafe MOB boat is cradled to port and davits for the Viking liferafts are provided on both sides of the vessel.

    Viking Energy is equipped with dynamic positioning to DnV AUTR class, using a Kongsberg Simrad DP system. Rolls-Royce provided the propulsion and manoeuvring outfit, comprising two main Contaz 25 azimuth thrusters powered by 3,000kW ABB motors, two 1 000kW tunnel thrusters and an 880kW ULE1201 retractable thruster, all electrically driven.

    The accommodation is spacious, finished mainly in light colours with wood trim, and has 12 single berth cabins and six two berth. In the wheelhouse, there is a console facing the bow for transit conditions, and two identical stations looking the other way, with controls and data screens from with the operators have a good view over the working deck. Main controls are duplicated at the bridge wings.

    Using LNG as a fuel means a higher capital cost for the ship. The attraction is a cut in NOx emissions of about 200 tonnes per year compared with vessel using oil, and a major reduction in carbon dioxide. Statoil can use this saving as a quota to offsetagainst other operations. A second factor is that Viking Energy is expected to use about 7,000 tonnes of natural gas a year. This helps to improve the economics of building LNG bunkering facilities at locations on the Norwegian coast to provide fuel fora growing fleet of gas-fuelled vessels in the future.

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