The electric propulsion revolution is happening, aided not only by fuel prices but also increasingly stringent emissions regulations coming out of Europe and the USA.

Unfortunately, neither the physics of the energy density available with current battery technology, nor the economics related to the cost of those batteries, quite stacks up for all-electric solutions.
An all-electric drive can only provide a limited running time with a short overall range. Extending that range requires eye-watering amounts of money and a massive weight increase (more batteries). Most fully-electric boats are custom designs, built to be super-efficient and often compromising on internal space, handling or ride comfort.

Which is why a hybrid drive may offer the best of both worlds. Engineers at world-renowned Christchurch company HamiltonJet have come up with an elegant, workable and cost-effective solution that combines an electric drive and an internal combustion engine, connected into the same driveline. Even better, this can be retro-fitted to an existing boat – as illustrated by the 14.5m catamaran Aria – the company’s recently-launched concept boat.
What makes this system different from other hybrid solutions is that the electric motor is located permanently in the drive shaft between the inboard engine and the jet unit. HamiltonJet managing director Ben Reed says there is almost zero power loss from spinning the motor when it is not needed, and it can be instantly activated into either engine or generator modes. The motors are remarkably small and in this case were fitted without needing to relocate the existing Yanmar diesels.

Aria was up in Auckland during the America’s Cup regatta for demonstration purposes to potential customers. The 19.5-tonne vessel started life as a recreational, foil-assisted catamaran designed by Teknicraft’s Nic De Waal. Built by Wanganui’s Q-West, she was set up as a family cruiser, not the usual platform for an electric drive. But she’s the perfect testbed for developing the technology and retro-fitting a hybrid drive system.
Reed says they’ve been involved in a number of electric and hybrid projects prior to this, but one of the practical problems boatbuilders face is some reluctance by individual suppliers to take overall responsibility for the project. So when two systems don’t play nicely together there are often issues with resolving the problem.

Since HamiltonJet provides marine propulsion systems, it made sense for it to expand its capability to provide the entire end-to-end solution. So HamiltonJet worked in partnership with Danish company Danfoss (one of the world’s leading suppliers of electric motors and drives), and Corvus (suppliers of battery technology) to supply, install and configure every part of the drive and control systems.
Another issue for anyone looking to install an electric drive system is the complexity of the components. It’s not just the motor and battery (together with a control system for regulating power to the battery), but also a battery management system to handle efficient battery charging. The batteries also need cooling, so an automated cooling solution is required.
With this hybrid drive, those same motors can function as generators (driven by the diesel engines), so a control system to feed the electrical output back into the batteries is required.
Lastly, for safety reasons the systems need to be fully redundant, with backup options should any component fail during normal operation. Which is why HamiltonJet acts as the system integrator for any project.
Because HamiltonJet already has a suitable control system (the AVX range), it has done extensive work to integrate AVX into the hybrid drive components. The objective was to make the system as easy to drive as a Toyota Prius – you simply drive it, without worrying about which mode to use.

At low speeds (such as around the marina) it runs fully electric. For cruising it is fuel-powered, and at wide open throttle, in boost mode, it can be both. And the batteries are automatically charged whenever the motors have spare capacity. Although the skipper can manually override which mode is used, he can also leave it to the computer to decide the most appropriate system to use at the desired speed.
Reed says the hybrid solution can be added to any of the company’s broad range of waterjet solutions, together with the AVX controls. Combined with GPS assistance, this integrates the steering and propulsion systems to provide pinpoint manoeuvring using a range of possible controllers – conventional helm, joystick, tiller or their ‘mouseboat’ three-axis controller.


The system is modular so various combinations are possible, and up to six waterjets can be controlled by the AVX. The hybrid system adds one more touchscreen to the helm station, displaying the current drive characteristics and allowing single-tap switching between modes.
Before starting to implement a hybrid solution such as this, HamiltonJet provides a free applications engineering and design service, working with the owners to decide what characteristics they want for the boat.
In the case of Aria the requirement was silent running in and out of the marina, and fully-electric propulsion at under 10 knots. So a 100kW electric motor on either side complements the twin 530kW Yanmar 6SY diesel engines.
A battery module of 78kWh allows around 40 minutes of running time in fully-electric mode, while 2,300 litres of diesel provides considerable range on the main engines. An HTX30 waterjet either side turns all that power into motion. At displacement speed the effective 100kW total output is more than adequate for moving the boat at a reasonable pace.

How does this hybrid perform?
In a word – astonishing. To be fair she was no slouch beforehand, turning up 37 knots at full roar from the diesels. But in boost mode (when the electric motors are also turned on) top speed jumps to 42 knots – almost fast enough to keep up with an AC75 foiling sailboat!
Perhaps more impressive for the intended use is the 9 knots under fully-electric drive, with enough battery power to get around even extended low-speed areas. And of course, under electric power she’s virtually silent so could slip into an overnight anchorage without disturbing the residents.
Overall, says Reed, the boat’s weight remained virtually unchanged with the hybrid system conversion. The 608kg of batteries was offset by removing some of the cruising equipment, such as a water maker, plus the separate genset (no longer required). The need for a new ratio meant that the original gearboxes were also replaced with a pair of ZF305-3 models – more compact and lighter – as were the latest generation of HTX waterjets.

Apart from the batteries and associated management systems, the other major new requirement was air conditioning – for the batteries!
Charging and discharging batteries generates heat, even when the very latest technology lithium nickel manganese cobalt oxide (LiNiMnCoO2) batteries are used. For safety reasons these are air-cooled, with a system capable of up to 14kW of heat rejection. The batteries are also individually fire-insulated, an important consideration in getting the all-important NZ Survey signoff.

The result is a superbly capable vessel, which from the outside gives no hint of its partly electric heart. The hybrid drive eliminates any of the ‘range anxiety’ sometimes suffered by electric vehicle owners, since Aria’s diesel tanks offer a huge range.
On the other hand, the electric drives reduce the load on the Yanmars, especially that low-rev period through the marina, and can considerably lengthen the time between services for those engines.

For more details contact Brendan Bourneat HamiltonJet on 03-962-0520 or visit