Converting A Speedboat To 100% Electricity

By Scott Masterson

I have been an avid boater and EV enthusiast for years. I do mostly pleasure boating and enjoy boating with a few exceptions:

  1. Waiting in line for other boaters to finish fueling
  2. Expensive repairs and lack of qualified mechanics
  3. Frequent maintenance
  4. The noise
  5. The smell
  6. The polluting of our lakes

scott-electric-boatI decided I needed a solution. Years ago I had converted my pontoon boat to all electric by replacing the ICE powerhead with a 15hp AC motor. At the time, my intent was to merely toddle around at hull speed, around 5mph. Since then, I miss being able to quickly go to the various points of interest on the lake. I originally thought of scrapping the 15hp AC motor and starting over with something more powerful, but then it occurred to me that if getting somewhere quicker is my new quest, a pontoon boat is not the most efficient boat to try to go fast in.

My thoughts went to a speed boat. After a long thought about how fast, how long, and how much, I decided on a 17.5 foot bowrider. There were several reasons why. First, I started to look into what motors were available with what horsepower and for how much. I found that boats over 18.5 feet in length would require motors at and above 200hp. I quickly noticed that there is a large difference in cost between making up to 150hp vs 200hp in electric. The leap from 150hp to 200hp is almost double with the currently available options. The second consideration to the length is the size of my garage. A 17.5 foot boat just makes it.

So I came to the conclusion that my ideal motor will have around 150hp peak. As a side note, don’t let anyone tell you that an electric motor will have four times the power of an ICE. There is no substitute for horsepower. That being said, pick a motor that has the same peak power as the ICE you are replacing. The next requirement for the motor is to provide enough continuous power to maintain a good cruising speed, (between 25 and 30mph works for me). By using calculators I found online and asking people in the know, I determined that right amount is 50hp. The next choice is air or liquid cooling for the motors and controllers. I chose to liquid cool due to the air circulation limitations and the continual power demand, which is more than a car.

The next task was to put a battery pack together. I chose a controller that was rated 120V max with 200 amp continuous. The choice in motor was actually a dual motor, so two controllers were required. The total max continuous output is 120V, 400 amps. This is typically where I cruise at. Each controller is capable of a peak current of 650 amps for 2 minutes, for a total of 1300 amps. Working backward from the controller requirements, I chose to construct a pack with an emphasis on maintaining the controllers continuous requirements of 120V, 400 amps. I did not concern myself so much with the peak power requirements because I knew I would never run at those levels for more than a few seconds. I ended up using 57V 57Ah battery modules made by Tesla, two in series, five in parallel.

Now that I had my major components researched, I set out to buy a boat to convert. My original plan was to buy a used boat in good condition, but maybe with a blown motor, that I could buy cheap. Unfortunately, I could not find one. All the used boats available for sale with a bad motor I could buy cheap were in poor condition. Instead I changed my mind and went with a brand new 2016 Bayliner 175 Bowrider. I had the dealer pull a brand new 3.0L motor and deliver it to me on a pallet along with my brand new boat with no motor in it.

I put the boat in my garage and went to work. The conversion was surprisingly easy. I used the existing rear mount with the help of an adapter plate I designed, and I modified the front mount to make it possible to mount it to an adapter plate as well. For the most part, I am using the original mounts. The motor came together with the outdrive in a similar fashion. I used the existing flywheel and coupler and simply made an adapter to attache the original coupler to the motor. The original throttle and shifting linkage were relocated. There was no alteration need for the shifting linkage. The throttle was simply attached to the motor’s electric throttle.

The motor is cooled by means of circulating transmission fluid through both the motor and controllers by means of a 12V pump and a marine heat exchanger. A little wiring and a little plumbing later, I was ready to hit the water. The first time I went out on the lake, the adapter I had connecting the motor to the coupler walked down the motor shaft and the coupler started to scrape against the flywheel housing. I took the boat back to the garage, pulled the motor and discovered that one set screw on the shaft key was not enough. I add another set screw to the top of the adapter to meet with the key and another on the opposite side where I actually drilled a whole in the motor shaft so I could screw another set screw into the motor shaft itself. I have taken the boat out numerous times since and that appears to have solved the problem. That being said, there was very little re-working of the original conversion plan.

The boat performs very well. My original range estimate was 25 miles. At that time, I was carefully making shorter runs until I was more confident in my build. I was only using 20% of the battery each run and that was easily giving me an eight mile round trip. Since then, I have made runs closer to 15 miles round trip and I’m still only using 40% of the battery. I feel confident that a 30 mile range is easily achieved. I will continue to push the envelope.

So how has my boating experience changed? Lets go back to the things I didn’t like about boating that I mentioned earlier. Here’s how things have changed:

  1. Waiting in line for other boaters to finish fueling. (Now I just plug in at my marina. Next day I come out, it’s charged up and ready to go.)
  2. Expensive repairs and lack of qualified mechanics. (With the conversion to electric, many of the components that exist on an ICE motor do not exist on an electric. No starter, no coils, no injectors, no fuel pump, etc.)
  3. Frequent maintenance. (Now that it’s all electric, no need for regular oil changes, plugs, wires, belts, fuel filter, etc.)
  4. The noise. (No noise with electric.)
  5. The smell. (No smell with electric.)
  6. The polluting of our lakes. (No polluting with electric.)

These days, I simply have the marina’s valet take my boat from my stall and put it on the water. When I’m done, they put it back in the stall and I plug it in. All done. I guess only time will tell if all this will work out. For now, it’s boating heaven. For more information and videos, follow this link:

2 thoughts on “Converting A Speedboat To 100% Electricity

  1. Awesome work! That’s the future!

    I only wish you could convert one for me since I’m not good with this kind of stuff. You should definitely think about selling these.

    Can you please tell us more about the costs for the conversion?

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