Balance of Power

A DIY diesel-to-electric repower required a lot of education but only a little engineering.

Issue 143: March/April 2022

While motoring my 1968 Mason 40, NorthWind, out of the marina on a beautiful spring morning on Puget Sound, smoke began billowing up through the companionway, and I quickly glanced at the engine temperature gauge to see it climbing fast. My first thought was, “Not again!”

I shut down the engine, ducked below, and pulled up the floorboards to the engine compartment. Our old Perkins 4-108 had blown a hose—the same one we’d replaced a few weeks earlier. Instantly, I knew we were going to need a tow back to the marina, and by now, the BoatU.S. towing crew were not strangers to us.

All of which gave me plenty of food for thought later as NorthWind rested in the boatyard undergoing some restoration work. I began wondering if I should finally repower. I’d already spent a lot of money on the boat during this refit, but my overall lack of trust in the old Perkins convinced me that now was the time.

First, I contacted the local Beta dealer and discussed a Beta 38 or 43. Beta motors have a good reputation for reliability and ease of maintenance and repair, so they were a logical choice. I thought it would be the simplest option since I was pulling out a diesel, and dropping one in its place should be easy. Right? Not exactly. The Beta dealer said everything except the fuel tanks should be replaced, including fuel lines, exhaust components, hoses, shaft, propeller, and shaft bearing. This quickly added to the total cost before we even discussed the installation, which prompted me to expand my search to electric motors.

 

 

Learning the E-Options

To educate myself about electric, I commenced conversations with representatives from Oceanvolt, Elco, and Electric Yacht. All were easy to reach, quick to respond to questions, and helpful in planning my potential repower.

Truth be told, I had long pined for an Elco motor—they have a long and excellent reputation—so they were the first company I contacted. Their motors run at a higher voltage than the others I considered, which meant battery planning would be a challenge. I thought the EB-40 (40-hp comparable) would be the best Elco model for NorthWind. This motor required 108 volts, which made sourcing batteries difficult and way over my budget. That being the case, I went back to the Internet in search of a 48-volt system.

Oceanvolt, also a reputable manufacturer of electric and hybrid systems, offered several 48-volt motors. However, I soon learned that these would be quite underpowered for my 40-foot, 12-ton, full-keel sloop. They recommended their 20-kW shaft motor. Oceanvolt bundles a battery into a complete system with all their motors over 10 kilowatts, and they provided a professional, extremely detailed quote for a very smart system.

But even though I knew any repower is more than simply the cost of the motor, my back pocket, where my wallet usually resides, was starting to cause some pain.

Accepting once again that repowering was not going to be cheap, I contacted one more 48-volt marine propulsion company that I found in a magazine article, Electric Yacht. I liked that I could search the company’s website, pick out a motor, add it to the cart, check out, and pay with a credit card, as if I were buying a book online. And because I’m an engineer, I appreciated the spec sheets and drawings they provided so that I could plan accordingly. Electric Yacht’s other big selling point is the assurance that their motor is easy enough to install that somewhat handy do-it-yourselfers can do it, potentially saving me thousands of dollars in installation costs.

Choosing the Batteries

I spoke with one of Electric Yacht’s representatives, who helped me determine that the QT20 (20-kW) motor would be a good match for NorthWind, and if I wanted to use LiFePO4 for my battery bank, I would need a maximum continuous discharge of over 416 amps. Meeting or exceeding that in my battery bank should prevent the battery management system (BMS) from shutting the batteries down or limiting the full available power from the QT20. (Incidentally, using the motor settings in the display, you can limit the power of the QT20 for battery banks with fewer maximum continuous amps, allowing people to start with a smaller battery bank and build onto it over time. This flexibility can help keep initial costs down.)

There are so many battery options out there, and most of the chemistries on the market—AGM, Gel, or LiFePO4—will work with the Electric Yacht motor. LiFePO4 lithium batteries have grown enough in popularity that the prices have gotten competitive. They’re only a little more expensive than similarly sized AGM batteries, and they have many more charge cycles, so I wouldn’t need to replace them as often. In for a penny, in for a pound; if I was going to the trouble and expense to repower NorthWind with an electric motor, I should have a LiFePO4 battery bank.

I found Big Battery out of Southern California, which offers LiFePO4 batteries in many configurations and stocks several that are 48 volts. They provide a 10-year warranty, and their customer service and tech support are easily reachable. Since this was my first installation of this magnitude, I knew I might need last-minute questions answered and problem-solving assistance throughout the process. I purchased four of their Husky 48-volt 103-Ah batteries. At 6,700 maximum continuous watts or 139 discharge amps, I could get by with a minimum of three; however, a fourth came with a deep discount, so I went with that.

The batteries arrived first—four of them filled a pallet! The motor came next and included everything, along with a display to replace the diesel engine’s gauges and a single throttle control lever for both forward and reverse—a welcome change for NorthWind. Only some wiring components not attached to the motor—such as those for the main battery switch—weren’t included; my Electric Yacht rep explained that this is because each installation is different, and the wiring for each is customized. While some boat owners need longer wiring runs to accommodate batteries and associated components in various places, I was able to fit the entire QT20 system and the 48-volt battery bank in the same deep bilge space that once housed the Perkins 4-108 and transmission.

For the complete Electric Yachts QT20 motor package and the Big Battery 48-volt bank, I was into this project for just less than $18,000—about 25 percent more than the cost of a new diesel (but no fuel). Although I did not need to replace my drive shaft, propeller, fuel lines, hoses, and exhaust system, I did need a 48-volt battery charger. I added a 340-watt 4-volt solar panel, solar charge controller, and a small 2,000-watt gas generator as emergency backup. Those add-ons came to an additional $1,500, putting me slightly under $20,000 for the complete system.

The Install

Once the old diesel engine was pulled, I prepped the space by running 4-x-4 frames to mount the new motor and routed in a 1-inch-thick plywood bridge to hold the battery bank. I coated all the new wood with a good boat paint, since there wouldn’t be stray oil spray or drips to protect it from moisture.

The mounts that came with the QT20 package allow for wide adjustments, so it was easy to mount the motor into the same cradle as that of the diesel. The QT20 only weighs 135 pounds, so a friend and I easily lifted it down into place and bolted it in. We mounted the batteries on the new platform right behind the motor.

In between, I built a bracket/mount for the parallel box for the battery bank and mounted the detached relays for the motor. The wire installation took nearly all day (it’s not easy to cut or bend into position 4/0-gauge wire). Finally, I installed the display and control lever in the cockpit and ran those wires back to the motor.

By now it was fall, and not wanting to spend winter in the boatyard, I splashed NorthWind and returned to my marina some 25 miles away with parts of the refit incomplete. Since some key equipment still wasn’t installed (including my windlass and running rigging), I opted for a tow to my homeport, rather than do a full sea trial on my new engine.

Still, while under tow I tested the system’s regeneration capabilities— recharging the batteries while the propeller spins. Being towed at a steady 5 to 6 knots, I was pleased to see the motor returning 160 to 200 watts of charge back to the batteries. This was great news, since it doesn’t take a lot of wind to get NorthWind to 5 to 6 knots under sail.

A few weeks later, I headed out for a short sea trial. I easily got the boat to 5 knots, about cruising speed, for two hours as I crossed Puget Sound and back. Back in the marina, I plugged in the 48-volt charger, and its display showed that I had used about half the battery bank.

I’m planning more tests after NorthWind’s restoration is further along and I can factor in the solar panel’s effect on the battery bank’s charge level. Over time, if I decide I want more range, I can add more batteries, since I have all that space that once held two 50-gallon fuel tanks.

Overall, this project has been an education and actually a pleasure. I am looking forward to exploring my home waters from a brand new, e-powered perspective.

Larry Ordoins has been living aboard, sailing the Salish Sea and down the Pacific Coast for over a decade now. His 1968 Mason 40, NorthWind, is a wood hull, offshore sloop he has been restoring for the last few years in preparation for more Pacific Coast travels and beyond.

 

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