A new generation of Rotortugs

ART 80-32 Hybrid demonstrating its agility (photo courtesy Hans Hoffmann)
ART 80-32 Hybrid demonstrating its agility (photo courtesy Hans Hoffmann)
RT Evolution has a specially configured Alphabridge Tugboat console with all of the essential controls within easy reach
'RT Evolution' has a specially configured Alphabridge Tugboat console with all of the essential controls within easy reach
All of the Hybrid controls and manual engine stop-start buttons are located on a single panel on the wheelhouse console
All of the Hybrid controls and manual engine stop-start buttons are located on a single panel on the wheelhouse console
The forward winch and towing staple onboard RT Evolution
The forward winch and towing staple onboard 'RT Evolution'
RT Evolution before launch showing its smooth double chine hull design and triple-thruster configuration
'RT Evolution' before launch showing its smooth double chine hull design and triple-thruster configuration
The RT Discovery completed by Cheoy Lee is equipped for fire-fighting
The RT Discovery completed by Cheoy Lee is equipped for fire-fighting

The first four Advanced Rotortugs of the ART80-32 class, incorporating the unique triple Azimuth drive concept, were delivered to their owners Elisabeth Ltd during the last two months of 2014 for use by Kotug International. 'RT Evolution' and 'RT Emotion' with Hybrid propulsion systems were built by Damen Shipyards Hardinxveld –Giessendam in the Safe Ltd facility in Gdynia and are currently stationed in Rotterdam.

A second pair RT Discovery and RT Endeavour were delivered by the Cheoy Lee Shipyards in Hong Kong, to the same owners for use by Kotug and their joint venture partners in Port Hedland, Western Australia. These two vessels represent the first part of four-tug order placed with Cheoy Lee, with the prospect of further additions in the near future. This batch are virtually identical to the Hybrid version, described in this feature, but have diesel propulsion systems, slight differences deck machinery, and are equipped for fire-fighting.

The ART 80-32 was designed by naval architects and consultants Robert Allan Ltd (RAL) of Vancouver with significant input from Kotug and Rotortug BV reflecting some 25 years of consolidated operational experience. After previously working together on several design projects an agreement between Rotortug BV and RAL was signed in 2012 which made Robert Allan the exclusive designer of all Rotortugs worldwide. Likewise Damen Shipyards and Cheoy Lee Shipbuilders were given the right to build and market Rotortugs as part of their own sales portfolios.  

The hullform for the ART 80-32 incorporates many features developed by RAL for high performance escort tugs and adapted to suit the Rotortug concept to provide enhanced stability, sea-keeping and escort performance. The design process involved a detailed Computational Fluid Dynamic (CFD) study of different hull forms to determine the preferred hull characteristics. After considerable research the resulting double chine hull incorporates a pronounced sheer, a semi-raised foredeck, small bilge keels and sponsons to minimise the possibility of ‘deck-edge immersion' during escort operations. At the same time it was essential to retain and enhance the Rotortug’s unique omni-directional manoeuvrability and shiphandling characteristics.

Design and construction of the new ART 80-32 series meets the class requirements of Lloyds Register of Shipping with the following notation:+100 Tug+ LMC,UMS,IWS. They are vessels of 491gross tons, measuring 31.95m in length overall, with a beam of 12.60m and a maximum draft of 6.93m.

On trials all four tugs achieved bollard pull figure exceeding the specified 80 tonnes pulling in either direction along with a free running speed of 13.5 knots sailing ahead and astern. The agility of this new breed is spectacular, manoeuvrability and station keeping are quick and precise, along with side stepping capability to port and starboard at 7.5 knots.

When RT Evolution, the first Hybrid version of the ART 80-32, arrived in its home port of Rotterdam it caused considerable interest. Your MJ correspondent is grateful to Kotug and Rotortug BV for the privilege of visiting and taking a trip on the new vessel.

At first sight RT Evolution is of a spacious and clean design an impression that prevails throughout the vessel. The decks and full height bulwarks have been kept as free as possible from unnecessary obstructions and the inherent sheer of the hull is plain to see. Shiphandling fenders at the bow comprise an upper row of 800 mm diameter cylindrical rubber moulding with a lower course of ‘W’ section moulded rubber blocks. The stern is protected in the same way and the sheer lines have two rows of ‘D’section 300 mm x 300 mm lightweight Polymarine foam moulding.

A single drum, electrically driven towing winch, manufactured by DMT, is installed fore and aft. The forward winch incorporates a windlass for the vessel’s single anchor. The drums on both winches have a brake holding capacity of 230 tonnes and accommodate a 230m towline of 80mm diameter ‘Ultra-line’, with a 20m forerunner (pennant) of 64mm diameter Dyneema  connected by means of a Kotug patented ‘ ‘Ko-link’. The towline from each winch is deployed via an ‘A’ configuration tubular towing staple lined with stainless steel. The precise positioning of the staple on the deck forward and aft is critical in order to provide a safe and effective tow-point.

A spacious engineroom houses all three main engines, two auxiliaries and most of the necessary ancillary equipment. Each of the "C" rated, IMO Tier II Compliant, Caterpillar
3512C HD main engines is rated at 1765 kW (2365bhp) running at 1800 rev/min. Power is transmitted from each main engine to a Schottel SRP 3000 fully azimuthing thruster with a 2.3m diameter fixed pitch propeller, via a Twin-Disc MCD 3000 LD slipping clutch.  Also located in each shaft-line is a Westinghouse-Teco 500kW motor/generator.

The Schottel azimuthing thrusters, two forward and one aft, are located in separate compartments separated from the engineroom by transverse bulkheads and watertight doors. Each unit is fitted with frequency controlled electric steering motors designed to achieve the required response time of one 360 degree rotation in 16 seconds.

RT Evolution has two auxiliary generators of different capacities. A Caterpillar C18 diesel driven generator of 450ekW provides current for the Hybrid propulsion system and winches. A smaller Caterpillar generator C9 of 200 ekW supplies the ship’s systems, battery charging and the Hybrid system when required.

Two Corvus Lithium Polymer battery packs are housed in a specially designed compartment adjacent to the engine room, with its own ventilation, monitoring and alarm systems.

Access to the engine room is through the engine control room and its adjacent switchboard room at main deck level which to offers a degree of acoustic isolation from the crew accommodation.

The Xeropoint Hybrid power integration system installed in RT Evolution and its sistership was devised by the Canadian company Aspin Kemp Associates Ltd (AKA) and is a refined version of that developed for use in Kotug’s hybrid Rotortug the RT Adriaan. The latter was one of an earlier series of Rotortugs built in 2010 and retrofitted to become Europe’s first true Hybrid tug in November 2011. RT Adriaan has been in service almost continuously since its conversion and has achieved a reduction in fuel consumption of approximately 15% and reductions of 44% Hydrocarbons, 33% NOx and 38% SOx emissions. The new ART 80-32 Hybrid Rotortug is expected to improve on those figures thanks to the vessel’s improved hullform and hydrodynamic characteristics.

An important advantage of the Hybrid system is to ensure that the diesel engines onboard the vessel are operating as close as possible to their designed optimum and most efficient condition. In most diesel driven tugs the main engines only operate at maximum power for as little as 2% of their working lives. With a hybrid propulsion system much of the slow speed, low load, operation is carried out using electrical power from the batteries or from diesel generators operating close to their most efficient condition. Among the added advantages are reduced maintenance costs due to lower main engine running hours. Reduced noise levels in a Hybrid vessel improve working conditions for the crew. In all Rotortugs there is greater propulsion system redundancy thanks to the triple thruster configuration. In the Hybrid the electric motors are also available in the event of a main engine failure.

The Hybrid propulsion system is very simple to operate from a panel on the wheelhouse console. 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 on the overhead console 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 switchboard 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 8 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 shaft-line on batteries alone, enabling the tug to maintain position with a maximum speed of 3 knots for about 1 hour.

With TRANSIT 1 selected the thrusters are powered by the motor/generators with both auxiliaries running to give vessel speeds of up to 7 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 to 13.5 knots. The motor/generators supply the vessel services and any surplus power is used for battery charging.

The wheelhouse aboard RT Evolution is one of the vessel’s most striking features offering exceptional all-round visibility through full height windows. Located in the centre is one of the first Alphatron – Alphabridge Tugboat consoles to be fitted in a vessel of this type. Comprising two ergo dynamically designed consoles with a central Captain’s chair mounted on rails, the consoles contain the majority of controls and instruments required to operate the tug. At each end of both consoles is a semi-retractable screen, one with the radar display, switchable for the river and sea sets, and the other a multi-function screen displaying navigational and other functions. The Captain’s chair can be turned and positioned to face in either direction and the displays are arranged to ensure that the screen functions are always in the same position. All of the other controls and instruments are cleverly grouped together on purpose designed panels. An overhead console is provided for radios and other instrumentation and includes a centrally mounted screen showing the Xeropoint data.

RT Evolution has fully climate controlled accommodation fitted out to a high standard for a maximum of six persons, although in Rotterdam a crew of three is the norm. The main deckhouse contains the entrance lobby, galley, mess, a WC and two single en-suite cabins for the Captain and Engineer. The lower deck contains two double berth en-suite cabins, a laundry, and galley stores.

By Jack Gaston

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