In March 2012 Europe’s first true hybrid shiphandling tug, the RT Adriaan, entered service with the KOTUG fleet in the port of Rotterdam.

Known as the E-KOTUG, the vessel was the result of a carefully planned and executed conversion of an ‘almost new’ ‘Rotor Tug’ built in 2010. Since returning to service, RT Adriaan has worked very successfully as part of the very busy fleet operating throughout the Rotterdam/Europort area. With more ‘hybrid’ Rotor Tugs planned, KOTUG kindly invited your correspondent to spend a couple of days aboard RT Adriaan for a first hand look at the operation of this ground breaking vessel.

RT Adriaan is a 32m tug built in 2010 by Niigata Shipbuilders in Japan and powered by the unique Rotor Tug triple unit azimuthing ‘thruster’ propulsion system, comprising three main engines producing a total of 6,884 bhp to give a maximum bollard pull of 84 tonnes towing ahead, astern or sideways.

The vessel was converted into a fully functioning ‘Hybrid’ tug in a little over three the Padmos shipyard at Stellendam and retrofitted with a XeroPoint Hybrid Propulsion System designed by Aspin Kemp & Associates (AKA) of Canada. Prior to the conversion of its own vessel KOTUG was inspired and encouraged by the world’s first two hybrid tugs operated by Foss Maritime of California, which also have similar AKA power management systems.

During the conversion process electric motor/generators and clutches were installed in the driveline of each of the three propulsion systems. The XeroPoint hybrid power management switchboard was installed and wired in to the existing auxiliary generators, the newly installed motor/generators and a Lithium Polymer battery pack. An essential part of the conversion process is to optimise the XeroPoint power management system, to ensure that the vessel operates efficiently in each of it’s ‘hybrid’ modes and, if required, reverts to a conventional diesel tug.

The main objectives of this and any other hybrid tug is to significantly lower emissions, lower fuel costs by optimising fuel consumption, reduce maintenance costs and engine running hours, lower noise levels and improve working conditions for the crew, and improve propulsion system redundancy.

In a conventional diesel powered tug the main engines and the diesel driven auxiliary generators are rarely operating in their most efficient mode, which is heavily loaded. Studies have shown that during harbour towage, 100% of full load (maximum bollard pull) on the main engines is used for only 2% of their operating life, leading to very poor fuel consumption and excessive exhaust emissions. Much the same can be said for the auxiliaries that spend much of their time idling or lightly loaded. Prior to conversion, RT Adriaan always operated with three main engines and one auxiliary generator on-line, meaning that the engines were operating well below maximum efficiency most of the time. With a ‘hybrid’ the Captain is able to choose the mode of operation most efficient for the job in hand.

At first sight RT Adriaan looks little different from other Rotor Tugs of the same class and is well equipped to carry out a full range of towage operations with exactly the same capability as its sisters. While working in port the tugs normally operate with a crew of three and sometimes with an additional trainee. Captain Jasper Goedhart and chief engineer Willem de Boer, along with ABs Soutaiman Zarouel and Gertho Beishuizen, are well used to visitors and a deluge of questions regarding their unique vessel. MJ is grateful for their help and hospitality.

In the wheelhouse are all the familiar controls, instruments and displays associated with the propulsion system, winches, navigational and communications equipment, all mounted on the split console and overhead panels. In common with all Rotor Tugs there are three Schottel hand controllers, one on either side for the forward thrusters and an additional one on the portside for the aft thruster. The only evidence of the tug’s hybrid propulsion system is a small panel marked Hybrid Marine Power System on the starboard console and a small electronic display panel.

Two small rotary switches on the panel, with associated indicator lights, give the Captain complete control of the hybrid system. One selects HYBRID or NON-HYBRID propulsion. The other selects any one of five operating modes: STOP – IDLE – TRANSIT 1 – TRANSIT 2 – ASSIST. The Xeropoint Hybrid colour display screen mounted close by shows in diagrammatic form the entire propulsion system, the active components and the flow of electrical and diesel power. A similar display is mounted on the AKA control cabinet in the forward thruster compartment.

With HYBRID selected on the switch panel and the mode selector set to STOP, no engines are running and the vessel’s own electrical system is fed by the battery pack via the main switchboard. When fully charged the batteries can maintain vessel services for up to eight hours. Once the battery capacity falls below 30%, one auxiliary generator will come on line. Alternatively, if shore power is available the batteries can be charged and the vessel systems maintained.

In the IDLE mode thrusters are powered by the motor/generators in the shaftline on batteries alone, enabling the tug to maintain position with a maximum speed of 2.5 knots for about half an hour.

With TRANSIT 1 selected the thrusters are powered by the motor/generators with both auxiliaries running to give vessel speeds of up to 6.5 knots. The vessel systems are supplied and any surplus power is used for battery charging.

With TRANSIT 2 selected the port and starboard thrusters are powered by their electric motor/generators from the main switchboard and the centre (aft) main engine drives the aft thruster to give a vessel speed of up to 11 knots. The motor/generator in the aft shaft line acts as a generator and if necessary one auxiliary will go on-line automatically.

In the ASSIST mode all thrusters are being driven by the main engines for towage assistance and speeds of up to12.5 knots. The motor/generators supply the vessel services and any surplus power is used for battery charging.

The engineroom aboard RT Adriaan houses three Caterpillar 3512 C-HD main engines, delivering a total of 3 x 1,765kW (6,884 bhp), two Caterpillar C9 250kW auxiliary generators and one 36kW Caterpillar C4.4 harbour set for use when shore power is not available.

A 500kW TECO-Westinghouse motor/generator is neatly installed in each shaftline close to the flexible coupling of the Schottel SRP 1215 FP azimuth thrusters. The main electrical switchboards are located against the forward engineroom bulkhead.

Forward of the watertight bulkhead, is a compartment containing both forward Schottel thrusters. Electrically powered variable frequency steering motors have replaced the original hydraulic equipment. The compartment also houses the Corvus battery array made up of 12 Lithium Polymer packs connected in series and rated at 78kWh with a nominal voltage of 532V. Nearby is the AKA XeroPoint power management switchboard and engineroom control panels.

The power management system, controlling both AC and DC supplies, is complex and a full description is well beyond the space allocation for this feature.

As a direct result of the Hybrid conversion, KOTUG quote an approximate reduction in fuel consumption of 20% and the following percentage reductions in emissions: particulate matter -44%, unburned hydrocarbons -48%, Nitrogen Oxide (all NOx converted to NO2) –32%, CO2 -35%.

During the MJ stay aboard RT Adriaan the tug was ordered to carry out three shiphandling jobs, two with incoming, heavily laden, bulk carriers of approximately 180,000 dwt. The trip out to meet both ships at about 8 knots was uncannily quiet with mode TRANSIT 2 selected and just one engine running. Once in position, ASSIST mode was selected and the remaining two main engines started automatically to give sufficient power and agility to make a towing connection. In the case of the first ship, Cape Canary, a towline was made fast to the bow from the aft winch. Working with two other KOTUG vessels, RT Champion and SD Shark, the ships were berthed some distance into the Maasvlakte complex.

For the second bulker, Nord Energy, RT Adriaan was made fast in the centre lead aft position from the single-drum forward winch. Prior to berthing the heavily laden ship was swung and towed stern first to the jetty, an operation made easier by the triple unit propulsion system, rapid reaction and bollard pull of the two Rotor Tugs. RT Adriaan’s third operation, carried out at night, was to assist a large Maersk container ship from its berth with no other tugs involved. TRANSIT 2 mode was used to reach the berth and while waiting for the ship to complete working, cargo IDLE mode, which was virtually silent. Once permission was granted to pass the towline at centre lead aft, ASSIST was selected. Using its powerful bow thrusters and the tug aft, the ship came neatly off the berth and within 20 minutes RT Adriaan was dismissed.