Passagemaker Magazine

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.