Marine Log - February 2009 - (Page 26) IC B Y J O H N R . S N Y D E R , E D I T O RE CLASS TANKERS HERE COME THE E xcept for a hybrid logo emblazoned on its superstructure, you wouldn’t know that the Carolyn Dorothy is different from any other tug you might see in the harbor. That’s because the Carolyn Dorothy’s secret lies below deck in its engine room, where you’ll find a bank of 126 gel cell batteries in high voltage cabinets. Unlike any other tug in the world, the Carolyn Dorothy is the world’s first hybrid tug. Unveiled last month during ceremonies on a gray, rainy day at the Port of Long Beach by Foss Maritime, the tug is a symbol of the bright future of green technologies in the marine industry. What’s impressive about the tug is that it is expected to significantly reduce nitrogen oxide, particulate matter, sulfur dioxide and carbon emissions, while providing the same performance as conventional tugs. Designed by the world renowned naval architectural firm Robert Allan Ltd., the Carolyn Dorothy is the tenth Dolphin Class tug built by Foss Maritime at its shipyard in Rainier, Ore., so it shares the same hull as its nine sisters. That was one of the engineering parameters that Foss demanded when it set out to build its hybrid tug. The hybrid tug is 78 ft x 34 ft, with a depth of 14 ft and operating draft of 15 ft 6 in. Propulsion for each of the conventional Dolphin Class tugs consists of two Caterpillar 3512D HD Tier 1 diesel engines, rated at 2,540 hp each, that drive Rolls-Royce US 205 fixed pitch azimuthing stern drives via marine gearing. For the hybrid tug, the propulsion system consists of two Cummins QSK50 Tier2 diesel engines, with two Siemens Motor-Generators, two Cummins QSMII diesel generators and 126 gel cell lead acid batteries, which can be used in various propulsion modes with a pair of Rolls-Royce US205 azimuthing stern drives. The total horsepower is 5,080 hp. The Carolyn Dorothy will produce the same bollard pull—64-1/2 tons either ahead or astern—as its conventional sisters. It will be capable of running at 6 knots off of one generator and a top speed of 13-1/2 knots. 26 MARINE LOG FEBRUARY 2009 Other significant equipment on board includes a Markey DEPGF-42 bow winch and Schuyler Rubber fendering. As for the battery life, Foss Maritime vice president Susan Hayman says, “The replacement is theoretical at this point and is dependent on how often the batteries are discharged to low levels and brought back up again. We estimate the replacement will be in the range of 2.5 to 5 years. The batteries will be sent back to the manufacturer and recycled at that point.” HYBRID ADVANTAGES The advantages of the hybrid are that it optimizes the power sources (engines, batteries and generators) to run only when they are needed. The power sources run at or near their design point for maximum efficiency. One of the dilemmas for harbor tugs is that a lot of their time is spent idling at very low power levels where fuel consumed per horsepower produced is very high. With the hybrid solution, there is no unnecessary engine idling, thus reducing fuel wastage. Engines run at or near best efficiency, reducing emissions. Minimizing engine use also means that there is reduced operating and maintenance costs. Foss partnered with Aspin Kemp Associates (AKA), Owen Sound, Ontario, Canada, and its affiliate, XeroPoint Energy, on the hybrid technology. AKA designed, manufactured and installed the hybrid propulsion system. FOUR MODES OF OPERATION The Foss hybrid tug has four modes of operation: Minimal emissions for a power range of 0 to 5%, eco-cruise in the 6 to 22% range, mid-range for 23 to 46%, and full mode in the 47 to 100% range. • Minimal Emissions Mode is for idle periods and no-wake maneuvering. The main engines are off line. It uses battery storage for hotel load and station-keeping maneuvering. One genset comes on as needed to recharge batteries. Hotel load alone can be provided from batteries alone for extended periods. • Eco-Cruise Mode is a continuous slow transit and low power ship assist work. The generators or one main engine or both provide power for the Z-drives. The batteries provide “buffer” for transient load changes. • Mid-Range Mode is for continuous fast transit, controlled ship assist and barge movements. Generators and main engines provide propulsion power. The batteries provide transient ride-through. • Full Mode is for continuous fast transit and full power ship assist. Both the main engines, one or two generators and batteries are available for power. Foss says compared with the operating duty cycle of the conventional Dolphin Class tugs in San Pedro Harbor, there is a 44% reduction in NOx, 44% reduction in particulate matter and reductions in CO2 and SOx. Batteries www.marinelog.com SEE EXCLUSIVE VIDEO IN OUR DIGITAL EDITION Foss hybrid tug unveiled http://www.marinelog.com
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