Real Numbers For Electric And Diesel-Electric Drives


Note October 2020: Do not let the original date of this post and model dissuade you for using it. The basic physics have not changed since 2014 and you can change things like the price of batteries and efficiencies of solar cells to reflect changes since then.

I have always believed that one of the most important things you can do in sailing, as well as life, is do some basic arithmetic before you make a decision. That would seem to be self evident, but it’s amazing how many of us (I have made this mistake too) rush into things just because they are cool and/or the latest fashion without subjecting them to a bit of arithmetic rigour.

I guess the classic error in this regard is whipping out a credit card and buying something without doing the simple arithmetic to figure out how long it will take to pay down the card or how much interest we will incur while doing so. In the same vein, investing large amounts of money in electric or diesel-electric drive options without doing the maths first can be expensive, as well as extremely time consuming and disheartening.

The fact is that in many, perhaps most, cases such systems simply don’t work very well for voyaging boats, sail or power, as I discussed, along with doing some basic arithmetic with the help of engineers Eric and Matt, in this post. (You can also read a very well reasoned analysis by AAC Engineering Corespondent, Matt Marsh over at his site of why this is.)

Some people, after reading my post, came away with the idea that I had some kind of vendetta against electric and hybrid diesel-electric systems. But actually nothing could be further from the truth. I fully support their use, when they make sense.

But the big problem with making informed decisions about electric and diesel-electric drives is that although the caveats that Eric and I expressed in my last post on the subject are easy to understand and only require a bit of basic arithmetic, if you want to really examine how the various drive options that you are contemplating might perform with various different usage profiles, things start to get complicated and the associated mathematics beyond us lay people to reliably calculate.

Kind of reminds me of the investment industry that way. And just like in the investment industry, this level of complication lets some of the promoters of some of this new drive technology make a lot of wild claims with impunity.

So do I have a solution? Well, no I don’t…but engineer, sailor, AAC commenter, and all around smart guy, Eric Klem does:

Eric used his considerable experience with this technology to build a spreadsheet model that will allow boat owners to experiment on their computer with different drive systems for different usage profiles and see what the real effect is going to be of installing diesel, all electric, serial-hybrid and parallel-hybrid drives.

And most important of all, Eric’s model also spits out capital and lifetime costs, two numbers that many proponents of this technology are just a tad quiet about.

Download the model by clicking on the icon at the end of the post and have fun. (You will need a copy of Excel on your computer to run it).

I for one have had a fascinating time with the model and come to the conclusion that here at our Base Camp in Nova Scotia, where we could have her alongside our wharf plugged in, a day-sailer or small cruising boat with an all electric drive would suit Phyllis and I very well for cruising around Mahone Bay.

On the other hand, for the highly efficient hull form, long, thin, high-latitude expedition motor boat that I have been noodling around with for years, a good old fashioned low speed, high torque diesel, possibly turning a controllable pitch prop, is the way to go.

Thank You

A huge thank you to Eric Klem for this great resource. He came up with the idea and didn’t get a dime for the many hours building the model must have taken him.


If you have questions about the model or if in using the model you discover something interesting, please leave a comment. One request though, please include the relevant user input parameters that you used. And if you tweaked the base model in any way, please ‘fess up.

Click to download model
Like what you just read? Get lots more:

Learn About Membership

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 twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

Notify of
Inline Feedbacks
View all comments