Feature 2 | TUGS Greener future for tugs
Seattle-based Foss Maritime Company is due to release what is claimed to be the world’s first low-emission hybrid tug.
T
he hybrid Dolphin-class tug promises significant reduction in emissions and fuel consumption
whilst maintaining the same performance standards as her sister Dolphin- class tugs. The new 5080hp tug, Green Dolphin,
is being built at Foss Rainier Shipyard in collaboration with the ports of Long Beach and Los Angeles. The hybrid tug combines batteries, generators and main engines to reduce air pollution and offer greater fuel economy. The design represents Foss’ commitment to reduce its emissions profile. Tugboats, it would seem, are particularly
suited for hybrid technologies, as they have extremely high power requirements but for mostly short durations. Foss, partnered with Aspin Kemp
in the tug, and has a flexible design that allows it to be adapted to a variety of power and duty requirements. The system addresses some of the issues
experienced by harbour tugs, namely keeping engines running at or near their design points when needed, and shutting them down when not actively required, allowing the hybrid tug to develop the same high power and bollard pull as the conventional Dolphin class boat.
and
Associates (AKA) and their affiliate XeroPoint Energy, proposed a design based on Quanta distributed energy systems (DES) hybrid technology. The Quanta DES system is an existing hybrid technology that will be modified for use
Design advantages The proposed design runs on lower horsepower main engines than a conventional tugboat, which results in lower emissions. Another advantage of the new design is that it has four operating modes, thus taking advantage of the fact that tugboats mostly operate at the lower end of the total power curve. The four operating modes are Stop, Transit, Ship Assist and Battery Recovery. The majority of the time the hybrid tug will be utilising the motor generators and batteries. In comparison to the conventional Dolphin
Morgan Foss, sister vessel of the Hybrid Green Dolphin tug. The hybrid will look just like her but will have a different mechanical arrangement (credit: Foss Maritime Company).
class tugs, the hybrid uses a combination of smaller main diesel sets and larger diesel-generator sets, main shaft-driven motor/generators, batteries and state-of- the-art power conversion and control technology. The boat can operate in three configurations: direct-diesel, diesel- electric, and electric.
Generation The hybrid boat has two diesel auxiliary generator sets to supply electrical power for propulsion, hotel services for the boat and to charge the batteries as needed. The hybrid model incorporates four
Setting the hull for the hybrid tug, starting with joining the bow and stern, at the Foss Shipyard in Rainier, Oregon, USA (credit: Foss Maritime Company).
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power bands and four readiness levels. The readiness levels are mentioned above and the power bands are: minimal emissions, eco-cruise, mid-range and full range. The minimal emissions band is intended for inactive periods while the vessel is secured and not on shore power, while stopped at sea between jobs or when maximum continuous load does not exceed 5% for extended periods. The eco-cruise band gives the capacity for continuous slow transit, or low-power work such as barge
Ship & Boat International November/December 2008
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