Norwegian supply ships go gas powered

This year marks a remarkable double event in the Norwegian offshore industry with the delivery of the world’s first two gas-driven cargo carrying ships. These platform supply vessels, ordered by the shipping companies Eidesvik and Simon M?kster Shipping, will operate on a 10 year charter to Norway’s state owned energy company Statoil.

Eidesvik took the initiative for, and headed the development of, the gas-driven ship concept in close cooperation with Statoil. The project was aimed at limiting emissions from the Norwegian maritime industry. This three year development project culminated with the placing of the building contract for this duo with Kleven Verft in Ulsteinvik, Norway.

The first unit, delivered on April 25 and named Viking Energy, is the realisation of the vision of the ship owner Eidesvik that gas fuelled support vessels could provide a useful contribution to reducing exhaust emissions. Both this vessel, and the Simon M?kster owned and operated sister ship, to be named Strill Pioner (slated for delivery mid-July this year), are based on the VS 4403 design from Vik-Sandvik.

The ships will help Statoil to reduce both carbon dioxide (CO2) and nitrogen oxide (NOx) emissions across its range of activities, contributing to Norway’s commitments to the Kyoto agreement. To assist 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 thrusters with contra-rotating propellers for main propulsion. It is fitted with a Kongsberg Simrad DP2 dynamic positioning system.

This 94m long by 20.4m beam supply vessel has a displacement of 6,013 dwt at summer draught of 7.9m. The construction of the hull and superstructure was subcontracted to the Polish yard of Maritim in Gdansk from where it was towed to Kleven’s yard for outfitting. The vessel has been built to a very high standard, both technically and in terms of living conditions for the crew, with DNV Clean and COMF-V(3) class notations. On sea trials the noise and vibration levels under both transit and manoeuvring conditions were reported to be very low.

Machinery

Four main generator sets each rated at 2,010kW supply electric power for propulsion and all services, with ABB being responsible for the electrical system. The prime movers for the generator sets are four Wärtsilä 6L32DF dual fuel engines, designed to burn gas or oil in any proportion. For minimum emissions LNG will be used but, should the ship move away from an area where gas can be bunkered, the engines can run on diesel fuel, and the 116kW Caterpillar powered emergency genset also uses diesel oil.

Rolls-Royce provided the propulsion and manoeuvring outfit, comprising two main Contaz25 azimuth thrusters with contra rotating propellers and powered by 3,000kW ABB motors, two 1,000kW tunnel thrusters and an 880kW ULE1201 retractable thruster. This all-electric ship has a service speed of 16 knots.

LNG containment system

LNG is contained in a giant thermos flask in the middle of the vessel, well protected. The 220m3 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 -162?C. The tank in turn is fitted in a compartment with A60 fire insulation.

Safety

precautions are extensive and 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 20?C and 5 bar pressure. This is carried out by means of a hot water vaporiser unit attached to the gas cylinder consisting of two coils 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 was responsible for the ship’s complete LNG system up to the connections to the main engines.

Large cargo carrying capacity

Apart from its unusual fuel, the newbuilding is a normal PSV, able to transport all the usual supplies. Liquid mud is carried in eight tanks flanking the LNG system amidships while aft of this are a further eight pressurised tanks totalling 400m³ for dry bulk. Some 1,300m³ of diesel 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 sheathed in wood and has an area of 1,030m² and a deck load of 2,500t. Two Hydramarine deck cranes are mounted at the aft end of the superstructure, while a Norsafe MOB boat is cradled to port and davits for the Viking liferafts are provided on both sides of the vessel.

The spacious accommodation consists of 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 facing the stern with controls and data screens from which the operators have a good view over the working deck. Main controls are duplicated at the bridge wings.

Economics

Using LNG as a fuel meant a higher capital cost for the newbuilding compared to ships driven by oil while additional annual costs will amount to about $0.87 million. The attraction is a cut in NOx emissions of about 200t per year and a major reduction in carbon dioxide. Statoil can use this saving as a quota to offset against other operations. A second factor is that Viking Energy is expected to use about 7,000t of natural gas a year which will help to improve the economics of building LNG bunkering facilities at locations on the Norwegian coast to provide fuel for a growing fleet of gas-fuelled vessels in the future.

By introducing LNG as an alternative to marine diesel, the result will be an 85 per cent reduction in the outlet of NOx, 20 per cent CO2 and 100 per cent SOx. A complete business model has been developed, where commercial shipping in cooperation with a major energy company, utilises LNG as fuel for ship propulsion while the energy company, in this case Statoil as charterer, provides the economic basis for the ship operation and compensates the higher charter by including the environmental benefits in its own environmental accounting.

Safety

It must be possible to carry a certain volume of gas on board in a safe manner in order to use it as a fuel and Eidesvik emphasises that safety has been an important aspect of the project. Risk analyses have been used systematically and extensively as part of the development. The engine system is divided into fireproof and explosion proof zones, and a number of constructive safety measures have been incorporated. Eidesvik points out that customers and users will not notice anything different just because the ship is gas-driven.

These so-called dual-fuel engines give the shipping company substantial flexibility, which is necessary since LNG bunkering stations can only be expected to be in a few places along the coast as of yet. This type of engine was previously used in some power plants and on offshore platforms, but has never been used on ships. Operating conditions on a ship are very different from a power plant, with completely different requirements for load variation and adjustment. A lot of work has gone into developing solutions that provide a great degree of operating reliability while, at the same time, solutions have been developed with the aid of risk analyses that safeguard safety. Special systems and ventilation solutions have been developed to intercept any gas leaks and channel off any explosions with only limited local damage being caused.

New rules

During development of the gas-driven car ferry Glutra for MRF (M?re og Romsdal Fylkesbåtar), regulatory requirements were prepared to cover this project. These regulatory requirements were in draft form in the Norwegian Maritime Directorate and Veritas, but had not been coordinated and were in general not applicable to other types of ships.

The Norwegian Maritime Directorate then started preparing new regulatory requirements which it coordinated with DNV, which also adjusted its draft regulations. The result of this is that from July 1 2002 both the Norwegian Maritime Directorate and DNV have regulations for gas-driven ships. No other national authority or classification societies have this type of regulations.

The Norwegian Maritime Directorate’s new regulatory requirements stipulate that the shipping company will be responsible for internal control. This is to a great extent patterned on the petroleum legislation. This is a new challenge for the shipping industry and also gives shipping companies greater freedom in developing concepts.

Emission-free ships for the future?

Eidesvik sees that the environmental technology can be further developed and that the next generation of gas-driven ships probably can be simplified and made cheaper. The development of Viking Energy has shown the way towards new technology that can further reduce emissions such as engines powered by fuel cell generators which generate no emissions of NOx, while CO2 emissions can be halved in relation to diesel operation. By using hydrogen as an energy source instead of LNG, the emission of CO2 will also cease.

The Norwegian ship owner’s objective is to develop ships with this technology and assessments have been started. In this connection collaboration with the Oslo-based environmental organisation, Bellona Foundation, has been initiated. It will probably take some years before hydrogen ships become a practical and viable concept but Simon Eidesvik, Eidesvik’s managing director, believes that gas-driven ships will be a necessary intermediate stage so that the industry can become accustomed to the use of gas.