Home' Work Boat World : July 2009 Contents The world's reportedly "first true hybrid tug" was unveiled in
January 2009 in southern California, USA.
Named the 'Carolyn Dorothy', the tug is powerful, green and
quiet. She is likely to have many followers, as hybrid tugs are
expected to be a significant trend in the marine industry. Vacon AC
drives technology is used as part of the hybrid propulsion system.
A typical harbour tug has highly variable duty requirements but
a very inflexible power plant. This results in inefficiency, higher
costs and a negative environmental impact. Seattle-based Foss
Maritime, specialising in worldwide marine transportation and
logistics, decided to solve this problem and concluded that the
answer lies in hybrid technology.
Foss partnered with Canada-based Aspin Kemp & Associates (AKA)
and its affiliate XeroPoint to develop a unique hybrid energy
conversion and power management system that would be
environmentally responsible without sacrificing horse power or
manoeuvrability. With an efficient combination of batteries,
generators and main engines, the hybrid tug offers improved vessel
performance and lower fuel consumption, maintenance costs and
emissions. It is also quieter than its Dolphin-class sister tugs, when
operating on batteries that can be recharged using shore power or the
vessel's own electrical generating sources. Foss anticipates that there
will be a growing market for its "green" tugs in the years to come.
The 3,728kW 'Carolyn Dorothy' will be used primarily for
harbour assist services -- moving vessels such as tankers and
container ships in and out of the harbour and into their berths.
"Green" technology suitable for conversions
Tugs at Los Angeles and Long Beach spend up to 50 percent of
their time idling, with the main engines running and ready to
respond, but with no power actually being used for propulsion. With
the Foss' hybrid tug, energy when idling is provided by batteries or
smaller diesel generators, so the main engines no longer need to idle.
The hybrid tug provides the same high power and bollard pull as
a conventional Dolphin-class tug, but uses a power management
system that keeps the main engines running at or near their design
points when needed, and shuts them down when they are not
required. To support these requirements, the boat uses a
combination of smaller main diesel engines and larger
diesel-generator sets than on a conventional Dolphin-class tug,
main shaft-driven motor/generators, state-of-the-art power
conversion and control technology, and storage batteries. The boat
can operate in direct-diesel, diesel-electric, diesel plus electric, and
The design of the Foss hybrid tug makes it suitable for
converting existing harbour tugs of all types to hybrid vessels. The
flexible design of the tug means it can also take advantage of
emerging technologies such as improved fuels, for example
bio-diesel and ethanol. The tug can also utilise cleaner, less
expensive shore power to charge the batteries. The fuel efficiency
of the main engines or the diesel generators is improved by
recharging the batteries as required.
For further information contact:
Vacon, USA. Web: www.vacon.com
WORK BOAT WORLD July 2009 45
World's first true hybrid tug sets a new benchmark
The Foss-built 'Carolyn Dorothy' hybrid tug
Developments in MARINE ENGINES and PROPULSION SYSTEMS
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