My motives for going electric were both environmental and curiousity in origin. I had no previous experience with electric outboards, but have had plenty of experience with cantankerous petrol outboards and the joy of trying to top up a small outboard with petrol while leaning over the back of a pitching dinghy! Petrol on fingers is no fun for subsequent sailing and biscuit consumption.
An early challenge was finding useful information about the performance of electric outboards so I could choose an appropriate unit.
My choices and experiences follow.
The single biggest question was: How much power do I need?
This was not easy to resolve. There is no direct comparison between the power output of a petrol outboard's HP rating and an electric outboards output. In the end, I decided to aim for 1kW output as a conservative choice.
With this in mind, I went shopping. There was not a lot of choice in New Zealand at the time. The local Minn Kota folk I called could barely have been less interested. Eventually, I settled on an Epropulsion Spirit 1.0kW unit. One upside to this unit was it had a very nice battery included that floated. The downside (for me) was that with the battery on top, the motor was a bit bulky for the inboard space available. There is nothing wrong with the motor at all, it was just the constraints of having the motor inboard.
So, I modified the motor! The first thing I did was remove the top assembly of the motor and replace it with a custom wooden one that fitted more easily. The second thing I did was cut the cable that connects the battery to the motor and lengthen it. This meant I could stow the battery to one side and operate the outboard without the battery perched on top.
This worked fine.
I soon learned that 150W of power would push the boat along easily at 5kph and 200W would push the boat along at 6-7kph even with some gentle waves. I have rarely exceeded 400W of power and never hit full throttle. Even in strong winds and lumpy seas 400-500W of power is ample.
The great majority of the time the outboard is operated at around 200W output. This is all that is required for getting from one spot to another and dragging a lure while doing so.
The battery that comes with the outboard is fine. It is of 1kWhr capacity and therefore good for up to five hours use and around 25km of range - at 200W in calm seas.
I wanted a bit more though. I wanted to be able to blast around after fish with no range anxiety :-)
There were a few options: Buy another Epropulsion battery; buy a third party battery and drive the outboard directly; buy a third party battery and use this to charge the Epropulsion battery.
Purchasing another Epropulsion battery was not appealing. They are more expensive than third party options and can only be used to drive the outboard. Powering the outboard directly from a third party battery would be possible, but tricky. There is some handshaking going on between the battery and outboard for sensible reasons. It is not just a case of plugging a battery in! I devised a plan to do this, but decided not to.
I decided to go with using a third party battery to charge the Epropulsion battery. The main reasons were:
It was more simple than driving the outboard directly with a third party battery.
The Epropulsion battery can be charged while it is being used to drive the outboard.
The battery charges at around 200W, which is all I mostly use anyway. So there was no advantage to driving the outboard directly.
The lower current required for charging meant there was less demand on the third party battery and related electronics.
As far as battery chemistry is concerned I am a fan of LiFePO4. Whilst Lithium Ion batteries can be more energy-dense, they also can catch on fire and don't last so long. LiFePO4 batteries with a built-in BMS are rock solid and last a very long time. I chose two 48V 1kWhr LiFePO4 batteries. This tripled the range of the boat to around 75km under power in calm seas.
I went with 48V batteries as this was close to the outboard battery charging voltage of 46.2V.
There were two things to consider when powering the outboard via the charger port. One is getting a physical connection, the other is not harming the outboard electronics.
To connect the battery I cut the desktop charger cable and put a waterproof connector on it. It is now easy to either connect the Epropulsion battery to the desktop charger, or the third party battery.
The Epropulsion battery charges at 46.2V maximum and up to 4A. I am using a Riden RD6018 DC power supply to take the output of my LiFePO4 and make sure it conforms to the charging input specification for the Epropulsion battery. The Riden RD6018 is a great unit that allows the maximum voltage and current to be set, it looks after everything else.
Typically I wait until the Epropulsion battery is about 30% down before turning the Riden unit on. This then starts charged the Epropulsion battery, which is often fully charged by the time I get back to the marina!
The single biggest lesson I learned is how much power is required for the Pathfinder. I now know that a 500W outboard would have been fine.
So.... if doing this again I would get a smaller outboard without a built-in battery. The main reason for this is that physical size matters for me, given that this "outboard" is actually inboard!
I love being in control of the power supply so I can use it as I choose. Purpose made batteries for the motor are fine, but you can't charge your phone with them.
I LOVE having an electric outboard.
It is quiet. It is clean. It starts with the touch of a button. There are no servicing hassles. It is very robust as water as water is concerned, you can dunk it and it keeps going!
It is ridiculously cheap to run. For less than NZ$1 I can charge all three batteries and buzz around for say 75km. Wow!
Yes, the upfront cost is more than a small petrol outboard. But that is life. I am happy to pay for better.