Electric and Hybrid Marine Technology International speaks to electric and hybrid marine propulsion consultant Jamie Marley who built an electric catamaran powered by twin outboards.
How did the idea of building your own boat come about?
I had previously converted a 6m RIB to full electric, and learned a whole lot from the project. But in my eyes, that was relatively easy as I used a commercial-off-the-shelf (COTS) electric propulsion system. If I was to gain an in-depth understanding of a complete electric propulsion system, I needed to build it from the ground up. I also needed greater range and some redundancy, so I went down the catamaran route this time.
I wanted complete control and understanding of the propulsion systems, and love the second life, recycle and reuse mentality. It was also particularly important to me, as an impartial consultant working in the marine electric propulsion sector, that I did not have or own one particular manufacturer’s system.
What was the timeline of the project?
We contracted the boat builder to start laminating in June 2020. I started building the electrical system immediately and fitting out the console. We received the hull in January 2021 and launched her in November 2021.
How is the vessel in the water?
The trim is near perfect, she hits the designed hull speed of 25kts, and is a great platform to work on and for recreation, due to the size. She sits no lower than other versions that are set up with IC engines and all the commercial fishing gear fitted.
How did you right-size the battery capacity and the motors?
The boat builder was able to inform me what was possible with ICE engines (twin 115bhp/84kW), so that gave me a starting point to understand what power I’d need. The Nissan Leaf EM57 electric motors are rated at 80kW, so I knew I was in the right ballpark. I knew that the Tesla Model S modules were suitable and gave me the best Wh/kg I could easily get my hands on at the time. I physically sized up the spaces within the hulls, and designed and built battery boxes that would give me just over 60kWh per hull/system. This capacity would enable me to operate her for reasonable periods at the hull’s eco cruise speed, which was reported to be around 16kts. Having now run her for over a year, I am very content with the total kWh capacity and am now focusing on optimizing how she operates, to gain added range.
Why Nissan and Tesla systems?
The Nissan motors physically fitted beneath the Mariner Optimax cowls and were able to be controlled by a COTS solution. The Tesla batteries gave the right kind of weight-energy density that I knew I needed to keep the catamaran at a low total weight. The Tesla module slave boards were also able to work with a COTS solution.
How complex was the process of integrating the motors?
Now that I’ve done it I would say not so hard. But I do recall many hours of research and head scratching. As I mentioned, what made the Nissan Leaf motors usable was a COTS solution that I found from a Canadian manufacturer, which basically means we could control the motors’ direction and RPM from a 0-5V throttle input.
Were there any challenges when assembling the system?
One of the longest head scratches I did was over the throttle. Marine throttles control not only the revs but also the gears, which in turn means you go forward or backward. The COTS solution was designed for a foot pedal with a direction switch. I needed to convert my standard marine twin throttle levers to work. A friend pointed out that mechanical throttles work in the same linear way, so I sourced a linear potentiometer and ditched the rotary version I had been fixed on.
I also admit that the Nissan Leaf EM57 Gen 2 motor was my third attempt – I had originally converted the Mariner Optimax outboards with the Mitsubishi Outlander PHEV’s rear motors, then a 110kW Nissan Leaf motor. No control solution was available for the Outlander motors or the 110kW Nissan motor, so I had to revert back, finalizing on the 80kW Leaf motors.
During energizing, I also realized that I’d wired the Tesla modules’ BMS slave boards up incorrectly, so I had to re-enter each of the HV battery boxes in situ to rectify. This was not an easy task. The Nissan motor also requires water cooling via a marine heat exchanger. I did not pay enough attention to the design of this system, so it was a real devil to fill and then continued to get air locks when the outboards tilted. I’m pleased to say I’ve now nailed this by positioning the circulation pumps in the lowest location in the cooling circuit.
How did you test the system before launch?
I was able to run up all parts of the system while the catamaran was ashore, even connecting a water supply to the outboards so I could spin them up. There were lots of challenges when energizing, simply because the components and system parts had, in many cases, never been put together in a propulsion system, or even a vessel. I was only really able to load the motors up when the boat was launched. I never opened up the throttles while tied alongside, but I did get some way to redesigning the marina’s sea bed, which was often churned up for hours on end.
I also started building in monitoring, and was able to get a vast amount of the data, logging and details up onto a Raymarine Axiom MFD (multifunction display), something that has been of great benefit operationally, and for me professionally. The systems run well, there were no temperature issues and plenty of power to enable her to run at a maximum of 25kts, plus economically at around 15kts, planing.
Finally, would you do a project like this again?
I think my marriage might last, but I don’t have the heart to put my wife through all this again! But to answer the question… absolutely. I’d love to build an oceangoing, live-aboard, full-electric, self-sufficient catamaran.
This article was originally published in the April 2023 issue of Electric and Hybrid Marine Technology. To view the magazine in full, click here.