A Tug Like No Other

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By MarEx 2018-03-02 21:39:00

Last month, Dutch towing group Muller Maritime took delivery of the harbor/escort tug Multratug 32. Despite the long number in its name, it is both the first in its class and the first vessel of its kind.

Designer Robert Allan Ltd. calls it a "Carrousel RAVE Tug," or CRT, and it integrates two features into a novel new package. First, it has two Voith cycloidial drives arranged fore and aft (the Robert Allan-Voith RAVE design). Second, its towing winch is mounted on a giant circular bearing - the "Carrousel Towing System" - which sits around the entire wheelhouse. With these design elements the tug can rotate with a load on its line, without fouling the towline on its own superstructure or girting. It is designed to pivot relative to its direction of travel, creating drag with the width of its hull. 

Robert Allan says that it is the tug’s relative heading that determines the magnitude of the towline force. At speed, large forces can be generated by applying a small amount of thrust to change the tug's orientation to the escorted vessel. The propulsion system is primarily used to control the tug’s heading, position and speed - not to generate bollard pull. 

Robert Allan Ltd. says that this provides inherently safer towing and escort operations, with enhanced maneuverability in confined waterways. It can exert thrust at towline angles not practical for previous generations of tugs. It produces escort steering and braking forces approximately 50 percent greater than any other type of tug of similar size, at greater transit speeds and with reduced risk. This means that it can get the job done with less installed engine power, improving fuel economy and exhaust emissions.

Robert Allan, Voith, Theodor Buschmann GmbH and Damen’s Maaskant Shipyards all contributed to the multi-year effort to design and build the vessel. Multraship and Novatug provided input from their experience during the development, construction, and operation of the first Carrousel tug, Multratug 12.

"The first trials showed that the tug is fully controllable, fast, powerful and has fully fulfilled the designer’s and owners expectations," Robert Allan said in an announcement. "The [CRT] can be considered a fully proven, state of the art ship-handling tug and definitely not just another experiment."