Electric Outboard Motors
This past summer I tested the latest generation of electric outboard motors from Torqeedo. These are much more efficient than traditional electric outboards, but with this advance comes a quantum leap in sophistication and electronic complexity.
I find it intriguing that these outboards have been designed by landlubbers. One of the owners of Torqeedo, Dr. Christoph Balin, bought a house on a German lake where the use of fossil-fueled motors is banned. He acquired a skiff with a traditional electric outboard motor. He and his friend Dr. Friedrich “Fritz” Bobel took one look at this outboard and said, “This is a horrible motor. With new technology we can do three times better than this!” Christoph conducted a market study and Fritz a technical study. They decided there was a viable business model and launched Torqeedo in 2005 with an initial goal of producing motors at least twice as efficient as the competition.
Having no previous experience with electric outboard motors, they were unhampered by preconceptions. Their single-minded pursuit of efficiency led them to adopt a new generation of brushless permanent magnet electric motors driven by electronically controlled pulse width modulated motor controllers. (If this sounds complicated, it’s because it is.) This is the same technology now used on a much larger scale in almost all hybrid boats. Fritz and Christoph made their motors small enough that they can fit inside a small pod not much larger than a propeller hub. Putting the motor right next to the prop eliminates losses that arise from transmitting power down a shaft through one or more right-angle bevel gears. Immersing the pod keeps the motor cool, an important issue in motors of this type. The motor controller is in the upper part of the outboard; all that runs down the shaft is the wiring between the controller and the motor.
To help with product development, Fritz and Christoph hired a German submarine propeller designer who used digital prototyping techniques to create four generations of propellers in six weeks. Along the way they learned that the key to propeller efficiency is large diameter and slow speed. Unfortunately, the only way to make motors small enough to fit in a pod is to have them run at incredibly high speeds (up to 30,000 rpm). So they designed a miniature 100:1 planetary reduction gear, which is also built into the propeller hub.
After eight weeks they had an electric outboard that was twice as efficient as traditional motors. They assumed this would stimulate rapid competition from bigger players, so they moved quickly and brought their motor to market in just 11 months. This was when they discovered that they had a lot to learn about the marine environment.
It’s been a painful few years coming to terms with corrosion and similar issues. Torqeedo’s outboards are already into their third generation and have gone through considerable re-engineering. This includes galvanic isolation of the electric motor, so no zincs are required on the shaft, and waterproofing to IP67, a standard that requires the entire outboard to withstand full immersion to a depth of one meter for 30 minutes. During one demonstration, a Torqeedo ran underwater until its battery went dead, and it still worked when recovered by a diver a couple of weeks later.
Regardless of how efficient and waterproof these outboards may be, their greatest weakness is the relatively low level of energy that can be stored in a battery as compared to a tank of gasoline. This, in turn, severely limits their range. To solve this problem, Fritz and Christoph designed their own lithium batteries to achieve the highest energy-to-weight ratios possible. As with any new technology, these batteries have had their glitches. But with around 15,000 of them now in service, Fritz and Christoph say they have seen “everything that can go wrong,” and have used this experience to create a new generation of battery packs.
One of the biggest problems Fritz and Christoph had to solve with their first-generation batteries was life expectancy. Given the high cost of lithium batteries, this is the single most important factor in figuring the long-term economics of operating one of Torqeedo’s outboards. Only time will tell whether these have been addressed in the latest generation.
We tested the Travel 1003 model on an Avon dinghy with an inflatable floor. Assembling and disassembling the Torqeedo control handle and battery pack is very easy. The units are amazingly light relative to the power they produce. There are no cranking issues–you turn the handle and away you go. It really is fun to putter around without the noise and exhaust fumes of a traditional outboard.
Somewhere inside the battery pack is a GPS receiver. Data from both this and the motor controller is fed to an LCD display built into the handle, which shows your speed over ground, the power being used, the state of charge of the battery, the remaining time and distance at your current speed and various error codes. It’s really impressive stuff!
At 4 knots with four people in our dinghy we had a maximum range of 8 miles, though this is very dependent on such factors as wind, waves and tide. We did not have enough power to get on a plane, but there is a larger Torqeedo model that reportedly can do this (though it requires a lot more battery power). The minute we tried to push the boat beyond 4 knots, our projected range dropped rapidly. Once the battery is depleted, it requires an overnight recharge to get topped up again. This, of course, requires an AC power connection, though there is an option to charge from solar panels.
Naturally, there are some things I would like to change. The screws and handles for securing the outboard to a transom seem somewhat flimsy to me, and there is no good way to protect the battery pack and handle from theft. The battery pack and handle also come off easily, which is a liability when lowering the unit into a dinghy or picking it up again. The natural tendency is to grab the handle, which immediately comes off, except for the wiring! Some kind of a lifting handle built into the battery pack would be really useful, but then I’d worry about the ability of the plastic locking pin for the battery pack to stand up to the shock loads that can occur in choppy conditions. Finally, when steering the unit turns too freely. It could do with an adjustable friction brake like those found on other outboards.
These, however, are quibbles. The greatest issues are range and recharging time. The Torqeedo’s range is more than adequate for puttering around a harbor, or between the boat and a beach, but will limit more adventurous cruisers, especially given the overnight recharging time. I’d like to see an option for a powerful fast charger. Most modern cruising boats have inverters large enough to recharge a battery pack in an hour.
Overall, this is a really impressive, beautifully engineered piece of kit that now appears to be well in tune with the marine environment. Assuming the new generation of batteries holds up over time, I’d be delighted to have a Torqeedo on my dinghy for short-haul applications, especially given its “green” credentials. For more demanding applications, unfortunately, there is still no substitute for the power and convenience of fossil fuels.
