When Electric Drive Works For a Cruising Sailboat

Block Diagram of Jimmy Cornell's System. Kindness of Oceanvolt

A few months ago several people wrote to me linking to an article by Jimmy Cornell in which he detailed the reasons for abandoning his Elcano Challenge, a project to sail around the world on an all-electric catamaran.

Ivan and Jimmy Cornell at Cape Horn on an earlier voyage.

Many people will expect me to start crowing about Jimmy's failure because I'm on record as being sceptical about both electric drive and electric cooking for offshore cruising boats...for most usage profiles.

Not a bit of it. In fact, I don't regard Jimmy's experience as a failure but rather, a real-world demonstration that going cruising with electric drive and sails as the only means of propulsion is practical, albeit at higher capital cost than most other options.

So let's analyze Jimmy's experience to figure out where he got it right (most of it) and what we could change to turn failure into success, without cheating by installing a generator.

Making It Work

You will notice that most anytime engineers like Matt Marsh and Eric Klem, who really understand this stuff, or even yours truly who rides on their coat tails, write about electric drive, the qualifier "usage profile" or some equivalent gets used—now you know why I put the term in bold above.

And that's really all we need to know to make electric drive work:

We must change our usage profile to fit the limitations and strengths of the technology. End of article...

...OK, that's not going to work, I can hear the howls from here.

So, first off, let's dig in to understand what went wrong for Jimmy. To do that, I suggest you read Jimmy's excellent and honest article, but here's the key quote:

Our 1000-mile maiden voyage from La Grande Motte to Seville showed up some of the weaknesses of the regeneration system when it failed to keep up with the overall consumption on a proper voyage, not during a test in calm waters. The consumption included both the autopilot and instruments, and also domestic demands such as induction cooker, microwave oven, two fridges, etc. My doubts started after we had sailed 82 miles in a period of 10 hours at an average speed of 8.2 knots. The net gain was a disappointing 9.5% of our total battery capacity, equivalent to 5.32 kWh, or 532 Watts per hour.

...I kept a detailed record over this entire passage, and the results were consistently and disappointingly the same...

Jimmy Cornell (emphasis mine).

At first blush that seems like a deal breaker, but let's not forget that Jimmy and his crew managed to sail the boat all the way from the south of France to the Canary Islands and back without burning a drop of diesel fuel, although, to be fair, I'm guessing they charged the batteries from shore power whenever they were in a marina. If so, some carbon was emitted, but a tiny amount. Whatever, an inspiring achievement.

Now, after that moment of optimism, I need to get realistic—electric drive fanboys will call it pessimistic—but don't despair, my ending is all optimism, so stay with me.

John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for 25 years, first in yachting magazines and, for the last 20 years, as co-editor/publisher of AAC.

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