<spanarial",sans-serif;>Un segundo par de remolcadores, el RT Discovery y el RT Endeavour, fueron entregados por los astilleros Cheoy Lee en Hong Kong a los mismos propietarios para su uso por Kotug y sus socios de la empresa conjunta en Port Hedland, Australia Occidental. Estos dos buques representan la primera parte de un pedido de cuatro remolcadores realizado a Cheoy Lee, con la perspectiva de nuevas incorporaciones en un futuro próximo. Este lote es prácticamente idéntico a la versión híbrida, descrita en este artículo, pero cuenta con sistemas de propulsión diésel, ligeras diferencias en la maquinaria de cubierta y está equipado para la extinción de incendios.

<spanarial",sans-serif;>El ART 80-32 fue diseñado por los arquitectos navales y consultores Robert Allan Ltd (RAL) de Vancouver, con una importante contribución de Kotug y Rotortug BV, lo que refleja unos 25 años de experiencia operativa consolidada. Tras haber colaborado previamente en varios proyectos de diseño, en 2012 se firmó un acuerdo entre Rotortug BV y RAL que convirtió a Robert Allan en el diseñador exclusivo de todos los Rotortugs a nivel mundial. Asimismo, Damen Shipyards y Cheoy Lee Shipbuilders obtuvieron el derecho a construir y comercializar Rotortugs como parte de sus propias carteras de ventas.  

<spanarial",sans-serif;>La forma del casco del ART 80-32 incorpora muchas características desarrolladas por RAL para remolcadores de escolta de alto rendimiento y adaptadas al concepto Rotortug para proporcionar mayor estabilidad, comportamiento en el mar y rendimiento de escolta. El proceso de diseño incluyó un estudio detallado de dinámica de fluidos computacional (CFD) de diferentes formas de casco para determinar las características de casco preferidas. Después de una considerable investigación, el casco de doble quilla resultante incorpora una marcada curvatura, una cubierta de proa semielevada, pequeñas quillas de sentina y flotadores para minimizar la posibilidad de "inmersión del borde de la cubierta" durante las operaciones de escolta. Al mismo tiempo, era esencial mantener y mejorar la maniobrabilidad omnidireccional única del Rotortug y sus características de manejo de buques.<spanarial",sans-serif;'>

<spanarial",sans-serif;>El diseño y la construcción de la nueva serie ART 80-32 cumplen con los requisitos de clase del Lloyds Register of Shipping con la siguiente notación: +100 Tug+ LMC, UMS, IWS. Son buques de 491 toneladas brutas, con una eslora total de 31,95 m, una manga de 12,60 m y un calado máximo de 6,93 m.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>FIRST STEER
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.

<spanarial",sans-serif;>At first sight <spanarial",sans-serif;>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. <spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>POWER APLENTY
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 <spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>XEROPOINT
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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>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.

<spanarial",sans-serif;>El puente de mando a bordo del RT Evolution es una de las características más llamativas del buque, ofreciendo una excepcional visibilidad panorámica a través de ventanas de altura completa. En el centro se encuentra una de las primeras consolas Alphatron – Alphabridge Tugboat instaladas en un buque de este tipo. Compuesta por dos consolas de diseño ergonómico y dinámico, con un asiento central para el capitán montado sobre rieles, las consolas contienen la mayoría de los controles e instrumentos necesarios para operar el remolcador. En cada extremo de ambas consolas hay una pantalla semiretráctil: una con la pantalla del radar, conmutable para los modos de río y mar, y la otra una pantalla multifunción que muestra información de navegación y otras funciones. El asiento del capitán puede girarse y orientarse en cualquier dirección, y las pantallas están dispuestas para garantizar que las funciones de la pantalla se encuentren siempre en la misma posición. Todos los demás controles e instrumentos están ingeniosamente agrupados en paneles diseñados específicamente para ello. Se proporciona una consola superior para las radios y otros instrumentos, que incluye una pantalla central que muestra los datos de Xeropoint.

<spanarial",sans-serif;> El RT Evolution cuenta con alojamiento climatizado completo y equipado con un alto nivel de confort para un máximo de seis personas, aunque en Rotterdam una tripulación de tres personas es lo habitual. <spanarial",sans-serif;>La superestructura principal alberga el vestíbulo de entrada, la cocina, el comedor, un aseo y dos camarotes individuales con baño privado para el capitán y el ingeniero. La cubierta inferior cuenta con dos camarotes dobles con baño privado, una lavandería y almacenes de cocina.

<spanarial",sans-serif;>Por Jack Gaston