Shop Talk BY CONSTANTINOS CONSTANTINOU
Our guest columnist, Cos Constantinou
of Greenline North America, explains the
design decisions that culminated in the sale
of more than 400 hybrid-powered boats, a
remarkable number given the worldwide
economic downturn.
Back in 2007 when our engineers first conceived the idea of designing and engineering a new boat propelled by diesel-electric
power, countless hours were dedicated
to defining the scope of the project, the
various key design parameters, along
with the specific type of propulsion
system that would best be suited to
the delivery of performance, as well as
reliability.
Two of the four main parameters
were not about propulsion per se. Our
engineers called for a slippery hull
with seakindly running characteristics.
Attempting to just drop an electric
propulsion system into a conventional
hull was the perfect plan for failure.
Enter our “Superdisplacement Hull.”
The second parameter, weight
optimization, was achieved using resin
infusion technology.
THE THIRD PARAMETER:
PROPULSION
For some time now, automobile
manufacturers have produced vehicles
with hybrid technology. In cars, the two
main types of hybrid technology are
parallel and series, with many variations
of each. However, boats are not cars,
the biggest difference being a boat’s
lack of ability to create regenerative
power either from friction or braking.
Combining the engine with the electric
motor, as is common with automotive
parallel systems, was rejected as a
solution since these fully integrate the
internal combustion engine with the
electric motor—without allowing one to
operate independently of the other.
On the other hand, a series system
was also deemed unsuitable, since
propulsion of the vessel would have
been restricted to the electric motors
only, while needing an auxiliary internal
combustion engine to recharge the
battery and extend the range. Instead,
working with a renowned automotive
industry supplier, Greenline developed
a proprietary propulsion system that
allows the vessel to be operated either
with electric motors or diesel engines–at
the operator’s discretion.
Greenline’s propulsion system
operates as follows: The electric
motor is coupled to the diesel engine
via a hydraulic clutch, and both are
connected to the same shaft. While
running the boat under diesel power,
the electric motor is connected to the
engine’s flywheel via the clutch. In this
operating mode, the diesel engine turns
the electric motor, and while doing so,
the electric motor generates power that
recharges the vessel’s lithium polymer
batteries.
With a flip of a switch at the helm, the
vessel’s operator can switch from diesel
propulsion to electric, whether that is
to conserve fuel or to enjoy the serenity
of cruising without any engine noise.
Engaging electric mode automatically
separates the electric motor from the
diesel engine by disengaging the clutch.
The vessel can be then put into gear,
and operate in zero-emissions electric
power.
The diesel engine and the electric
motors operate entirely independently,
the only interface being the shift/
throttle controls which are in turn
independent. The system’s design
and configuration thus provides full
redundancy, something that is of
fundamental importance in the marine
environment. This redundancy also
applies to port and starboard propulsion
packages, which operate independently
in diesel as well as in electric mode, with
dedicated lithium polymer battery packs
on each side.
Should the vessel experience any
technical issue related to the diesels, the
operator can easily switch to electric
mode and, depending on conditions
and battery charge state, can enjoy
an electric range of up to 20nm. If the
vessel experiences any issue with the
electric propulsion system or with the
charge state of the batteries, the boat
can be operated in diesel mode.
THE FOURTH:
VESSEL INTEGRATION
While the propulsion system is a
key feature of our boats, Greenline
Yachts are conceived in a manner that
maximizes livability. The boats have
open layouts, and plenty of natural
light flooding the upper deck as well
as the accommodations below. More
significant though, Greenline has
integrated the huge amount of energy
stored in the batteries with the house
electrical needs.
Greenline boats can operate
independently of a diesel generator.
All systems, including air conditioning,
entertainment, appliances, etc. are
powered by the lithium polymer
batteries, via an inverter. Without the
need for a noisy generator, life on board,
especially overnight, becomes a very
relaxing and calming experience. The
lithium polymer batteries are charged
via the boat’s solar panels when the
diesels aren’t running.
With full redundancy again in mind,
the lithium polymer battery system
operates entirely independently from
the other marine deep-cycle batteries on
board, which are typically two batteries
for the 12V consumers, one starting
battery for each engine, plus separate
batteries for the bow and stern thruster
if the vessel is so equipped.
Hybrid: Concept to Reality
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