of the main engines
online to provide the
necessary power.
The hybrid tug design minimizes fuel
consumption by using
a power management
system to match the
required power to the
most efficient combination of batteries,
generators and main
engines for that particular power level.
For example, instead
of idling the main engines while in standby
mode when alongside
a vessel, the hybrid tug
will run on battery
power with the main
engines shut down.
Foss’ “Eco tug” will still incorporate diesel engines to provide the power needed to guide containerships or pull a The bottom line is
loaded barge. In this hybrid design, Cummins QSK50 Tier 2 main engines rated 2535 k W will be used in lieu of the that the tug will re-
3788 k W engines used in the regular Dolphin-class tugs. The hybrid-electric system will feature two 500 k W battery duce all engine emis-
packs and two 275 k W Cummins diesel generator sets. sions and exceed
EPA’s Tier 2 emissions requirement for marine engines.
Initial estimates are that particulate
matter and nitrogen oxides are reduced by 44% for the same duty cycle
as the current Dolphin tugs operating
in San Pedro harbor.
The hybrid tug could also take
advantage of cleaner, less expensive
shorepower to charge the batteries. All
major container, selected liquid bulk
and cruise ship terminals at the POLA
will have shore-side electricity within
five years and all container terminals and
one crude oil terminal at POLB within
five to 10 years. This will allow shutting
down diesel-powered auxiliary engines.
The Foss hybrid is scheduled for
delivery to Foss’ Southern California
operations in 2008. The hybrid tug
will be introduced there because the
hybrid tug technology is best suited for
harbor tugs that need high amounts of
power for short periods of time.
Foss said the hybrid design will
make it adaptable for retrofitting of
existing harbor tugs and the tug also
has the ability to take advantage of
emerging technologies such as improved battery and fuel advances. A
designed what it called the world’s first
true hybrid tug boat. The hybrid
propulsion system will be installed in
Foss’ 23. 7 m Dolphin-class tugboat
that externally will look like its conventionally powered sisters and will retain
the Rolls-Royce azimuthing stern drives for propulsion. The hybrid tug will
be built at Foss’ Rainier, Oregon,
U.S.A., shipyard.
The “Eco tug” will still incorporate
diesel engines to provide the massive
power needed to guide containerships
or pull a loaded barge. In this hybrid
design, Cummins QSK50 Tier 2 main
engines rated 2535 k W will be used in
lieu of the 3788 k W engines used in the
regular Dolphin-class tugs. The hybrid-electric system will feature two 500 k W
battery packs and two 275 kW Cummins diesel generator sets. Although the
main engines will have lower ratings
than in the existing Dolphin tugs, the
vessels will have about the same total
3788 k W as its sisters.
When idling in a harbor or doing less
strenuous tasks, the vessel will rely on
battery power, supplemented and
maintained by the diesel gen-sets. This
will significantly reduce PM, NOx, SOx
field editor and CO2 emissions, Foss
said, and will reduce fuel consumption
and limit noise.
When working together, the batteries and generators can deliver nearly
1500 k W to the tug’s electric motors.
This level of power is enough for standby and slow-speed operations, which
accounts for a large percentage of the
operating time for a typical harbor assist tug. For example, tugs at the Ports
of Los Angeles and Long Beach spend
up to 50% of their time on standby.
In this parallel hybrid configuration,
electric power is transmitted to the
propulsion system via a pair of motor
generators. The main engines and the
motor generators are mounted on the
same shafts with clutching systems that
allow either or both power sources to
be used for propulsion.
A sophisticated power management
system brings batteries, generators
and main engines online for seamless
delivery of power, Foss said. For more
demanding situations such as moving
a ship or escorting, the power management system will bring one or two
