A small engine under the stern flap of the concept boat, but a big step for the boating industry – that, in a nutshell, is what Volvo Penta, the leader in marine diesel engines, and Beneteau, the world’s largest shipyard for leisure boats, presented in Sweden last week.
On the Krossholmen peninsula near Gothenburg, where Volvo Penta – similar to Mercury Marine in Lake X – has been researching and testing its prototypes for decades, float had the opportunity to get to know the new propulsion system before the public presentation and to drive it itself. The partnership between the two industry giants was announced at boot Düsseldorf in January 2023.
float gehörte zu den ersten Testern des Hybrid-Motors von Volvo Penta © Volvo / Hakansson
The approach is astonishingly simple: the combination of an electric motor with a conventional diesel engine from the Swedish manufacturer as a plug-in hybrid solves several problems of electric boating at once. Until now, there has been a technological barrier to combining fast speed and a decent range in electric mode for fast boats in family cruiser format.
How loud is quiet?
With winds of up to 24 knots and plenty of sunshine, we set off from the Penta Marina in Krossholmen with the Jeanneau NC 37 and the first ever international test crew. In hybrid mode, it goes out slowly, with only the electric motors running, where otherwise two Volvo D3 diesels work as standard. Two D4 diesel engines with 320 hp each form the counterpart in the stern of our test boat.
Compared to boats that run purely electrically, for example with the Deep Blue from Torqeedo, the first model from Volvo Penta is unusually loud to my ear. On the first day of testing, the noise development with the boat not yet optimally noise-damped is significantly higher than what I know from a high-voltage drive system.
The sound level is not disruptive; a conversation in the cockpit of the Prototpyen, under which the engines are working in the locker, can be held at any time. The next step, the Penta product engineer on board explains to me, will be to identify and eliminate the sources of noise that occur during purely electric operation.
Automatic change – and back
The two diesel engines switch on at around 1,500 engine revolutions per minute, just like in a car. Acoustically, it is very noticeable as soon as the conventional engine kicks in with its sonorous, typical diesel sound.
The fact that the electric motor sits between the diesel unit and the actual drive system like a narrow towel as a parallel hybrid means that the electric vehicle can simply stop at higher speeds and the diesel takes over. The electric motor then runs along, similar to the freewheel on a bicycle. In this setting, the running electric motor is used as a generator, which is driven by the diesel and can thus charge the batteries while driving.
Bei unserer Probefahrt... © Volvo / Hakansson
... geht das Boot schnell in Gleitfahrt... © Volvo / Hakansson
... und erreicht vor Göteborg 28 Knoten Maximum © Volvo / Hakansson
In the moderately choppy Baltic Sea off Gothenburg, we reach a maximum of 27 knots in fairly strong winds – with the diesel engines. This is a very decent top speed for the 37-foot Jeanneau family boat, which is usually equipped with D3 diesels. Under optimum conditions, the demo boat is expected to travel at 35 knots. With batteries, electric motors and control technology, the NC 37 weighs around 600 kg more than a conventional model.
Electric as a booster
If we reduce the speed significantly, for example when we are heading back to port and the engine is running more slowly, the diesel is automatically switched off in hybrid mode at around 1,200 rpm. The electric motor then takes over again.
If you want to accelerate from zero to the highest possible speed, this is done with the support of the electric motor. This is because the electric motor delivers its full power almost immediately, while the diesel is a little slower due to the system and has to get into gear first. It takes about six seconds for the boat to lower its nose and start gliding again.
Umgeschaltet zwischen den Fahrmodi wird im Hybrid-Display © Volvo / Isaksson
The seamless transition between electric driving and driving under diesel in “Hybrid” mode is charming. One click on the very tidy display is enough. Our test boat offers two additional driving modes: “Electric” as a purely electric operating mode for protected waters, and “Power” when it is important to reach a destination as quickly as possible with the combined power of the electric and diesel engines.
For the chronicle: In all-electric mode, our NC 37 reaches a speed of up to 10 knots. The range is 15 nautical miles at a constant speed of 5 knots. This corresponds to a travel time of around three hours before the diesels are back in operation.
Only a glimmer of silver can be seen
Der E-Motor sitzt schmal am Diesel Volvo / Isaksson
The batteries are located in storage compartments under the saloon and under the floor of the bow cabin. They are, of course, aligned with the boat’s center of gravity, so that the placement of the batteries has no influence on the boat’s heel. That would be even nicer.
We open the engine compartment and see that we can’t see much. Only a narrow, shimmering silver element between the diesel engine and the output to the Z-drive shows that this is the freewheel to the electric motor. With twin engines, as on our test boat, there are two electric motors with 2 x 60 kW continuous output.