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Three large new escort tugs contracted by Norwegian operator Ostensjo Rederi are to feature Wartsila dual-fuel engines integrated with a customized gas storage and supply system also supplied by Wartsila, the Finnish firm today confirmed in a statement.

The tugs are to be built to operate primarily on liquefied natural gas (LNG), but Wartsila points out that the dual-fuel engines will "provide the flexibility to select the most suitable fuel according to availability, price and local environmental restrictions".

The contract for the Wartsila solution was signed in December 2014. The design of the tugs was carried out by Canada-baed Robert Allan Ltd in cooperation with Ostensjo Rederi.

According to Wartsila, the overall LNG system, which incorporates its LNGPac fuel system, a fully integrated gas handling system, and the Wartsila Gas Valve Unit (GVU), has been "specially designed by Wartsila to accommodate the need for a compact solution".

The tugs are to be powered by 6-cylinder Wartsila 34DF dual-fuel engines. The Wartsila equipment is scheduled to be delivered during the first half of 2016.

"These are trend setting tugs in that they provide environmental sustainability through the use of LNG fuel. Wartsila is the technology leader in making this trend possible. At the same time, the flexibility of the dual-fuel engine technology also ensures a high level of operational security since the switch from gas to diesel can be made at any time without loss of speed or power," commented Carl Johan Amundsen, Project Manager at Ostensjo Rederi.

The vessels are designed to have a bollard pull of 100 tonnes, and are due to operate at Statoil's Melkoya terminal near Hammerfest, Norway.

"Wartsila and Ostensjo have cooperated closely to develop the chosen LNG solution for these new vessels," Wartsila said.

Ostensjo Rederi is a provider of offshore services and operates a fleet of 28 modern vessels. The company's tugboats currently operate at four terminals located in Norway, England and Ireland. The group has offices in Norway, the UK, Ireland and Malta.

Image: Ostensjo Rederi's offshore supply vessel (OSV) Edda Fram.