When Volvo Penta and the Beneteau Group team up on a quest to make sustainable powerboating a reality, it’s time to sit up and take notice…
The drive for a sustainable boating future is broadly divided into two camps – the passionate advocates of wholesale greenness and those who would welcome a workable market-ready improvement.
As we sit at Volvo Penta’s Krossholmen test facility a few miles north of Gothenburg, Sweden, the implication is that the world’s most prolific marine engine builder belongs to the more ambitious camp.
There’s a very clear understanding here that the hybrid diesel-electric prototype we’ve come to see is just one element of a multi-tiered approach that needs to include fuel cell development, fossil fuel alternatives, bio-sourced materials, efficient hull designs and end-of-life recyclability.
But if that all sounds a touch speculative, Volvo Penta’s new parallel hybrid system has already been operating successfully for several thousand hours on a wind farm personnel transfer vessel and on a support boat used by arctic surfers.
The fact that it’s performed so well means it’s now been integrated onto a leisure boat for the first time, and the test platform they’ve chosen to use it on is right here, waiting for us to take a look…
System basics
Jeanneau’s NC37 is a longstanding and well respected family sportscruiser. But when you lift up the engine hatch and peer inside, full of gleeful expectation, it all looks oddly commonplace.
What we have in here is a pair of Volvo Penta D4-320s hooked up to DPI Aquamatic Sterndrives. The engines have been shifted forward 25cm, freeing up the space for a pair of 60kW electric motors.
These are subtly (almost imperceptibly) integrated into the aft ends of the diesel engines with a freewheel clutch, so they can engage and disengage with ease.
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The electric motors are hooked up to a battery bank comprising eight modules with a total capacity of 67kWh. They’re mounted forward and split equally between the NC37’s starboard double berth and the space beneath one of the beds in the port twin.
The batteries themselves constitute 600kg of this system’s all-in 900kg – and while they take up quite a lot of space on a boat of this scale, the fact that they can be remotely positioned frees up plenty of volume in the engine room and enables much better distribution of the weight.
As regards the operation of the system, there are three basic modes: “Electric” mode engages the electric motors only, bringing you a 10-knot top end and a cruising range of 15nm at five knots.
The electric motors can be used to boost acceleration as well as for quieter slow speed cruising duties
“Hybrid” mode uses the electric motors for anything up to 1,500rpm before the diesel engines kick in. In this mode, the electric motors will then continue to aid acceleration whenever you push the throttles forward, before cutting out once you’ve reached your desired cruising speed.
When you then come back down off the plane and the revs drop to 1,200rpm, the diesel engines stop and the electric motors take over propulsive duties for displacement speeds.
The final mode is known as “Power”. This uses all four motors in unison, enabling you to get the full benefit of their combined thrust from idle right up to the 35-knot top speed.
As for charging, that’s done in three ways: by plugging into shore power; by automatically topping up while under way in Hybrid mode; or by hitting the Generate button at rest and running your diesel engines, bringing your batteries to capacity in just an hour.
On the water
As we get under way in Hybrid mode, a distinct whirring sound emerges from beneath the aft deck. It’s not unpleasant or intrusive but neither is it silent. If you imagine a food mixer in a neighbouring room, that comes pretty close.
We’re using the joystick at this stage and the fact that you can operate it with the electric motors means that, for the most part, there’s far less lag when you give it a tweak.
There’s no clunking in and out of gear either and with those 60kW motors, there’s loads of thrust too. But if you feel like the elements are getting too much, a simple push of a button enables you to re-engage your trusty diesels.
Hybrid display shows whether electric motors, diesel engines or both are being used as well as range and battery state
When we get away from the pontoon and transfer to the throttles, what’s really impressive is the way this system seems to alter your mindset. You find yourself reining in your right hand to avoid having to use internal combustion.
Then you look down at the data display and discover that 7 knots only gives you an hour of running time, so you ease it back to 5 knots, increasing the running time to three hours.
Then you ease it back again to 4.4 knots in a bid to mute the gentle splashing sound. And you feel good about embracing that serenity because you don’t need extra revs to settle down the vibrations or extra wind blast to whip away the fumes.
Conventional throttles control both the electric and diesel motors
When you do want to get up to speed, the results are again interesting. While the hybrid mode takes us from a standstill to 25 knots in about 19 seconds, the Power mode achieves the same feat in 12 seconds.
But of course these are software issues rather than mechanical ones and the transition from electric to diesel and back as you move up and down the rev range is very smooth and intuitive.
Notwithstanding the fact that it delivers a variety of largely superfluous data, the key elements of the digital interface (mode selection, battery state and time to run) are also pretty easy to use. But arguably the greatest reward is the way this system opens up your scope of applications.
Joystick control works even more smoothly in electric mode
You can sneak into a marina berth late at night or leave early in the morning without disturbing your neighbours. You can ease into a bay without scaring off the wildlife.
You can enjoy restricted waters conventional powerboats aren’t allowed to access and the fact that you have a relatively large battery bank means you can come to an anchorage for the night and operate all your domestic systems without having to kickstart a noisy generator.
More to the point, if you’re happy to sacrifice a little top-end speed, this system might also enable you to spec smaller engines on a large powerboat and then use the supplementary thrust of the electric motors when the time comes to get on the plane and cover some miles.
Twin 320hp D4s provide the diesel power
But of course, not every boat is a planing vessel and even those that are only spend a fraction of their time running at pace. The rest of the time, you find yourself pottering about at displacement speeds in estuaries, creeks, bays, anchorages and marinas.
Therefore a system like this that eradicates the noise, smells and vibrations when travelling at everything below 10 knots (without incurring the restricted range of a full electric boat solution) has the potential to improve your day’s boating to a really quite radical degree.
And yet as things stand, could you really call this a green solution in its own right? Probably not. After all, charging the batteries with your engines increases fuel flow, as does carrying around an extra 900kg in weight.
The electric motor only adds 25cm to the length of the engine
Batteries are also receiving some perfectly warranted criticism in terms of their green credentials because of the ecological and human impact of mining vast quantities of cobalt, nickel, manganese and lithium.
And although not the case in Sweden, the majority of users are likely to use fossil-fuel derived electricity to top up their battery banks from shore power.
Glimpse into the future?
It’s easy to imagine a time when a system like this might be combined with sustainably generated electricity and an affordable fossil-free diesel alternative like HVO (hydrotreated vegetable oil). That would create a realistic and desirable powerboating package.
There may equally come a time when potent, lightweight, recyclable battery banks change the conversation and necessitate a push for a sustainable future that eradicates internal combustion altogether.
But for now, where this system really scores is in its ability to leverage both electric propulsion and internal combustion for the things they do best.
The battery packs can be spread around the boat to balance the trim
You use the electric motors at displacement speeds, exactly when freedom from noise, fumes and vibration is most crucial. You can then engage your diesel motors when you want to get on the plane and achieve greater speed.
Whether a system like this also improves the eco credentials of motor boats is open to question, particularly given the temptation to activate the Power mode and enjoy a bit of extra poke.
But what’s not in doubt is the degree to which it can improve your day out. It marks a clear upgrade on a standard powerboat and it’s one for which we would happily pay a premium.
We don’t yet know how much that will be but we do know Volvo is committed to bringing production ready hybrid drivetrains to market in the next few years. If it can do this while adding less than 20% to the boat’s total price, that’s a powerboating future we could buy into.
First published in the August 2023 issue of MBY.
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