In November 2017, Østensjø Rederi’s LNG-fuelled escort tugs were jointly declared Tug of the Year by Tug Technology & Business.
Dux, Pax and Audax were singled out for the accolade due to several innovations, such as being the first tugs fitted with Wärtsilä dual-fuel engines and their ability to operate in extreme weather and sea conditions within the Arctic Circle in temperatures down to -20˚C.
The 40.2-m escort tugs were designed by Robert Allan as RAstar 4000-DF class tugs and built by Spanish shipyard Astilleros Gondán. They comply with IMO Tier III emissions standards, can achieve a maximum free-running speed of 15 knots and produce up to 107 tonnes of bollard pull.
The IMO Type C insulated LNG tank and regasification system is located below deck, with the dual-fuel main engines in a gas-safe (non-hazardous) engineroom. Østensjø’s tugs each have two Wärtsilä 6L34DF main engines with a power rating of 3,000 kW each, which drive transverse thrusters.
Schottel developed a specific type of thruster for these three dual-fuel tugs and six units with the new VarioDuct SDV45 nozzle were supplied to the Spanish builder. On each tug, Gondán installed two Schottel SRP 630 CP azimuthing propellers and an STT 170 fixed pitch thruster rated at 250 kW in the bow.
All three tugs are heavily fendered to protect them and the gas carriers even in extreme weather and sea conditions. They have bow fendering consisting of a 1,000-mm diameter cylindrical fender extending well aft along with a lower course of 400-mm thick W-shaped fender, which was specially designed to limit fender contact pressures to 20 t/m2.
The tugs have been providing escort services to LNG carriers at Equinor’s Melkøya production terminal since August 2017. They are also maintained in readiness for emergency services such as long-line towing, fire-fighting and oil spill response.