Dual-fuel technology meets owners’ needs

The Wärtsilä 50DF engine The Wärtsilä 50DF engine

Concerns over the extent and pace at which LNG will become obtainable as a marine fuel, and shortcomings in the international bunkering network, make dual-fuel (DF) machinery rather than pure gas engines the favoured choice for many owners looking to use natural gas fuel, writes David Tinsley.

DF plant may be regarded as the more practical option as concerns the recipient vessel’s trading or service pattern. Although the general view is that the price of oil will increase more than that of gas, opting for DF could also be a hedge against future price variations in an uncertain world energy market.

Due to be delivered from the STX Turku yard at the start of 2013, Viking Line’s 56,850gt newbuild ro-pax vessel will be the world’s first large ferry to use LNG as its main source of power. The Finnish ship will provide a milestone reference for DF engine technology, in the shape of four Wärtsilä 8L50DF prime movers, delivering a combined output of about 30MW.

With a maximum speed of almost 22 knots, the ro-pax will operate between Turku and Stockholm, carrying up to 2,800 passengers plus 1,300 lane-metres of trucks and 1,100 lane-metres of cars.

“LNG tends to suit ferries better than other types of vessel as they follow fixed routes between ports with LNG terminals in the neighbourhood, which makes them easy to bunker,” observed Matti Niskala, Lloyd’s Register’s country business manager for Finland, to the society’s publication Horizons.

“The ro-pax will be the first newbuild to comply with our (LR’s) provisional rules for LNG propulsion, although we’ve overseen and applied the same set of rules to a number of other vessels, notably the Accolade II bulk carrier, the world’s first LNG-fuelled ship,” said Niskala.

Led by the wide-bore 50DF type, which is said to have become the system of choice for LNG carrier operators favouring diesel-electric dual-fuel propulsion, Wärtsilä’s DF medium-speed engine family now also comprises the 34DF and 20DF designs.

Salient to future emission stipulations in designated sulphur emission control area(SECA) regions, Caterpillar’s deal this year to supply MaK M32C-based propulsion systems for Scandlines’ two ferry newbuilds in Germany included the option to have the five MaK 9M32C medium-speed engines retrofitted as dual-fuel units at a later stage if required.

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