Exclusive test: Powerful combination - Volvo Penta relies on diesel engines with electric drives
Torsten Moench
· 04.09.2023
Hybrid drives are nothing new. While they paved the way for today's fully electric vehicles in cars - we remember the legendary Toyota Prius - they have not yet been able to establish themselves in pleasure craft. The reason: there was simply no demand. Why would shipyards install such an exotic and expensive drive system if customers didn't want it and there were plenty of inexpensive combustion engines available?
This is currently changing. Firstly, customers have been sensitised and secondly, it is to be feared that the availability of marine combustion engines will also become more difficult in the future following the EU-wide decision to phase out combustion engines in motor vehicles. Volvo, for example, has decided to stop building vehicles with combustion engines from 2030 - that's around 6 1/2 years from now.
Whether this is the reason why the maritime sister company Volvo Penta is "stepping on the gas" when it comes to hybrid drives is pure speculation. The fact is, however, that the Gothenburg-based engine manufacturer is currently devoting massive resources to the topic of e-mobility on the water.
BOOTE was one of the first magazines to drive the prototype of the new Volvo hybrid drive in the company's own test centre Krossholmen near Gothenburg, installed in a Jeanneau NC 37.
Inconspicuous, but powerful
As you approach the boat, with the exception of the "Hybrid Electric" lettering, there is nothing to indicate the unusual drive system. Even when opening the engine compartment, the two disc-shaped 60 kW electric motors are barely noticeable. The space is dominated by the standard D4-320 engines with their auxiliary units. Only at second glance do you notice the inconspicuous but powerful electric motors between the engine block and the DPI-Z drive. The professionals call this a "plug-in parallel hybrid".
More striking are the 67 kWh battery blocks consisting of eight individual modules under the floorboards of the saloon. They come from MG-Energy-Systems in Holland, are manufactured to industry standards and are approved for commercial use on ships. Where the Jeanneau NC 37 otherwise shines with ample storage space, battery cells, cooling lines and thick cable harnesses dominate the scene here. All in all, Volvo puts the additional weight at 600 kg compared to the standard NC 37.
The first impression
Although officially declared as a "prototype", the entire drive and battery system makes an almost production-ready impression up to this point. But let's move on to the test drive, the reason for our visit to Sweden: when manoeuvring the hybrid NC 37 out of the harbour, it operates purely electrically up to around 1200 rpm (9 knots). In addition to the lack of engine noise, the perfect interaction between the Volvo joystick control and the electric motors is particularly noticeable. Thanks to the immediate application of full torque, even the slightest movement of the joystick is sufficient and the boat willingly follows every change of direction. There is also no more of the notorious "switching pops" of the drives from earlier times. Our test protocol: "butter-smooth manoeuvring control".
Volvo Penta installs three modes
We continue silently on the open water of the Gothenburg archipelago. We let the NC 37 run at a canal speed of around 8 knots and hear nothing! Only at 1300 rpm can the fully automatic starting of the two D4-320 diesel engines be heard through a slight vibration of the floorboards. The driver does not need to do anything. If he pushes the throttle further, the boat accelerates normally in planing mode and reaches its top speed at around 35 knots. We ease back on the throttle and the D4s resume operation at around 1300 rpm. The automatic start-stop system familiar from cars sends its regards. The boat now runs purely electrically again. As the driver, you can choose between three modes, which you can set on the touchscreen specially developed for this drive system:
- Fully electric - the diesels stay off, for example when travelling along a canal
- Hybrid - the standard setting
- Power
"Power" sounds exciting to our ears and we decide to try out this mode for the next test run. To explain: in "Power", the power of both systems, i.e. 2 x 235 kW diesel power, plus the 2 x 60 kW of the electric motors is added to a system output of 590 kW, i.e. a hefty 800 hp. Quite a lot for a 37-foot family cruiser and a challenge for the mechanics of the Z-drives.
This time, too, we drive slowly out of the harbour, but then put both levers "on the table" without a long preliminary skirmish. The result is impressive. Instead of 25 seconds from zero to 35 knots in hybrid mode, the NC 37 now accelerates to the same speed in 17 seconds. In plain language: if you give all four engines free rein, the boat accelerates around 30 % faster. Respect!
Volvo Penta provides sufficient power
The questions remain: What about the range and charging technology? If you drive the boat purely electrically at a displacement speed of around 5 knots, the end of the journey is 15 nm or the equivalent of three hours. Sounds meagre, but in practice it is often enough. And this is also where the advantage of the hybrid over the purely electric boat comes into play. If the route is longer, the weather is worse than expected or you want to go faster at some point, you don't have to worry about anything. Push the lever forwards, the diesels start automatically, take over the propulsion and automatically charge the batteries with up to 20 kW along the way. At anchor or in the harbour, the charging power of the D4 engines increases even up to 60 kW, so that the batteries are full again after an hour's "coffee break". A useful side effect: there is no need for an additional 230 V generator on the NC-37 Hybrid. Sufficient power is always available - as long as there is still diesel in the tanks. If you charge at the shore connection in the harbour, Volvo specifies a charging time of three to 12 hours, depending on the shore-side infrastructure.
To summarise: based on our experience on the NC 37, hybrid technology is a good compromise, but it is still quite expensive at the moment and the market launch is not expected for at least three to five years. Nevertheless, it combines the best of both worlds and enables carefree boating with the electric motor. Much like the Toyota Prius in its day.
Technical data
- Topspeed combustion engine:35 kn
- Topspeed electric:10 kn
- Range at 5 knots: 3 h/15 nm
- Power D4:2 x 235 kW
- E-motor performance: 2 x 60 kW
- Battery capacity:67 kWh
- Charging power D4 engines: 60 kW
- Charging power shore power:20 kW
- Charging time D4 engines:1 h
- Charging time shore power:3 h
- Drives: 2 x DPI Aquamatic
