Energy-efficient escort

Ship & Boat International: eNews September/October 2019

Luleå Hamn, manager of the port of Luleå on Sweden’s northern Gulf of Bothnia shore, has taken delivery of a multi-role capability escort tug designed by Vancouver-based Robert Allan Ltd (RAL) and distinguished by its combination of diesel main engines, shaft motor/generators and battery bank. Christened Vilja, the tug was built by Spain's Astilleros Gondan.

Despite typically experiencing ice cover between January-May, Luleå remains fully operational all year round. While the port has a mixed traffic, about half of the annual 8 million tonne cargo throughput comprises bulk goods.

Using her twin diesel engines alone, Vilja’s ahead bollard pull capacity is 85tonnes, but this can be upped to nearly 100tonnes by engaging electrical boost power.The tug also provides an early showcase for the Wärtsilä HY hybrid power module solution, providing functional integration of engines, energy storage system and power electronics, optimised for operation through an energy management system (EMS). The latter enables the tug to cope with the rapid load and speed changes inherent to its service profile, and one that alternates between normal summertime conditions and cutting through 1m-thick ice in winter.

The main machinery comprises a pair of 8-cylinder Wärtsilä L26-series diesel engines, each rated 2,720kW at 1,000rpm and driving a Kongsberg (formerly Rolls-Royce) US355 controllable-pitch, azimuthing thruster, capable of generating 3,100kW of power. Twin 1,000kW, in-line shaft generators-cum-electric motors and batteries provide extra boost. The configuration means the tug can run on batteries alone, or utilise a) a single main engine in hybrid diesel-electric mode, or b) both engines in diesel-mechanical drive with the option of boost power. The latter function is reckoned to yield a higher bollard pull than any conventional arrangement of comparable size. The system’s characteristics also feature a ‘smokeless’ phase, where no smoke is produced during start-up of the main engines.

Vilja has been accredited with Lloyd’s Register’s 1A Super ice class notation, and can break 1m-thick ice while maintaining a speed of 3knots. RAL, which used its TundRA 3600-H design as the template for the newbuild, lists the tug’s free running speed, ahead, as 14.6knots.

A Brunvoll rim-driven tunnel thruster, rated 300kW, has been installed in the forward part of the skeg for enhanced manoeuvrability. The two auxiliaries are Caterpillar C7.4 diesel gensets, each with an output of 118kWe.

TECHNICAL PARTICULARS

Vilja