One man’s experiment with electric propulsion

Electric vehicles (EV) are the future of light duty vehicle, with some forecast that put internal combustion engines (ICE) to soon be less competitive when compared to EVs. Other experts are more conservative on how soon this is going to happen, but it seems clear that ICE is fated to become obsolete as EVs are “the rational, economic choice”.

The simple yet powerful setup for Tesla S
The simple yet powerful setup for Tesla S  (photo by Oleg Alexandrov)

But what is the situation with marine electric propulsion? Can small sailboat be propelled by electric motors?

Over the water, the most common form of auxiliary propulsion for sailboats over 25ft is marine diesel engine. This proven technology benefits from many years of successful use and a well established industry of dealers and technical repairs. It’s easy to say that the diesel ICE dominates the market on sailboats. Before owning a boat with electric propulsion, my only experience was with diesel engines and, less often, gasoline outboards.

The engine room of a small sailboat
The engine room of a small sailboat (photo by PHGCOM )

Diesel fuel has a couple of good features: a high flash point that allows a relatively safe handling and a good energy density that provides satisfying motoring range with limited storage required. Today new, smaller and more efficient units fit easily in every engine room. Marine diesel give a sailboat an extended range under power and enough horse power to face any difficult situation.
When I first faced electric propulsion it was a quirky novelty, something I was not prepared to deal with. The most important discovery was that we all share a diesel engine bias. The common temptation is to approach the topic trying to ask the question if electric propulsion can replace the diesel engine.

After carefully going through a lot of research, re-doing myself the installation, and using it for more than 2000 nautical miles, I finally have an answer.
No, electric propulsion can’t replace the diesel engine. What it did for me was to change the way I see and use auxiliary propulsion.

It is common practice on a sailboat to turn on the engine not only when you need to maneuver around tight docks or anchorages, but also when wind or wave direction shifts to an undesired angle, when the speed drops under a certain threshold, if the battery charge is low or to fight against tides and currents. No matter what is the source of the annoyance, it takes little effort to fix it. Just turn the ignition key on, wait one second and put the throttle in gear and the problem is solved.
Fuel and general consumables are what sit between the choice of motoring or not motoring, and they are usually very easy to find everywhere and reasonably cheap. This mindset implies that power is abundant and available at all times, we can get to destination in less time, going through very little trouble.
Electrical propulsion on the other hand, requires a switch from this mindset, from considering power abundant to scarce. Scarce however doesn’t mean non-existent, it simply means that your reserve has to be cared for and maintained.

Tranquility, our Columbia 29 built in 1965 is powered by an inboard electric propulsion. The conversion from presumably an Atomic 4, was performed by a former owner who installed an earlier model from the company Electric Yacht. The motor is a simple DC Eltek brushed motor mounted on a 2 to 1 gear, and it works at 36Vdc-65Vdc (48Vdc nominal), with a maximum peak of 130Amps and 100Amps continuous. The power conversion is estimated equal to 6 horse power. It is small and weights a little more than 40 pounds.

Here is a video of Tranquility’s conversion to electric propulsion:

At the time of purchase the boat and the propulsion system needed serious updates, and we were forced to replace the existing battery bank with a new one. We opted for eight 6v Trojan T-125 batteries connected in series for a total capacity of 240ah at 48v. The reasoning behind the choice of a “traditional” lead acid 6v battery is both economical and practical. Lead acid batteries are at least five time cheaper than Lifepo4, and our sailing budget is very limited. Also, in case of a single battery failure it would be easier to replace one “golf cart” battery in different places of the planet, without dealing with expensive shipping and duties.
We use wind, hydro, the grid and fossil fuels to o recharge our batteries. In details, we installed a 48v wind turbine, a 20amp AC to DC battery charger powered by the grid when we are at the dock and by a portable gas generator when at sea, the 12×12 fixed three blade propeller that regenerates power under sail when boat speeds exceed 5 knots.

CRUISING WITH ELECTRIC PROPULSION: THIS IS HOW WE DO IT        With our current system we are able to motor in calm conditions at 3 knots while drawing 20 amps for approximately 15miles before we need any recharge. This estimated range is considered an ideal situation and we try to avoid to use our motor for that long. If we have to motor for more than 1 hour for instance, we would use our gas generator on deck to give some power back to the batteries. The motor rarely runs at more than 20 amps, and when it happens my hearth races as if they were taking my blood rather than electrons from the battery plates.
If we are drawing more than 20 amps it’s because we are fighting headwinds, currents in a narrow passage or a maneuver that requires high thrust, situations that should not last long if we plan our sail wisely and that not affect too much our power reserve. We always try to be very conservative with our batteries but at the same time we are happy to know that we can demand more power if conditions arise. How little we can motor became a game for us, and we feel particularly accomplished when we don’t use it at all.

Motor sailing on the Intracoastal Waterway
Motor sailing on the Intracoastal Waterway

Coastal sailing is the most demanding situation for auxiliary propulsion because of narrows, currents, navigational hazards that make sailing hard work and sometimes extremely time consuming. For these reasons, most of our sailing is done offshore where we don’t need auxiliary propulsion. Since we fixed our boat and hooked up the electric propulsion we have been sailing the East Coast of the United States from Massachussets to Georgia round trip with electric propulsion. As we are planning to take on more distance sailing, we considered that a successful test.
Occasionally we useD the ICW, especially on the southbound trip when we went from Norfolk, VA to Beaufort, NC. In that situation, time was a constraint as we were cruising in cold weather and our priority was to get south as fast as we could.
One day for example we needed to sail from Manteo NC, to Hatteras, NC via the Pamlico Sound. The forecast gave us very light wind for the next day, not great sailing conditions. If we waited, we would have to face strong headwinds for the rest of the week and get stuck there. Considering the scenario, We decided to leave early, hooked up our gas generator to motor all the way in a flat Pamlico Sound. Because of the short winter days we arrived at night but once there we had no worries about when to leave for the next leg of the trip that was done under sail.
The rest of the trip we sailed and motor-sailed along “the ditch”. A gentle breeze is sufficient to sail faster than we would motor, and we also tolerate to move slower if that is possible under sail. Carefully timing the tides we can motor faster using less power and so our journey is entirely planned in consideration of weather patterns and current.

Kate and I live aboard and cruise full time. So far electric propulsion has never been a concern, nor we live it as a limitation. After some adjustments in our cruising style, we quickly adapted to it. Cruising with an electric inboard propulsion means to compromise. The reduced range limits our possibilities in terms of routes and landing options. Sometimes it’s necessary to leave earlier from places we like to take advantage of a favorable weather window. Sometimes we had to stay longer in places we liked less. More than once a sudden calm, a favorable tide or other “disturbances” led us to places we din’t plan to visit. With this limitations, we learned that it’s not a coincidence that most of the main harbors are built in locations accessible under sail in most conditions, as historically that was the only way to get there.

Electric propulsion forces us to keep sailing even when the boat speed goes below 3 knots. These limits had forced me to work on having a better sailboat. Because of limited power we keep our bottom as clean as possible (I often dive myself or hire a professional when I don’t feel like). Because of our limited power, we purchased better sails for light air and installed a retractable bowsprit to increase our sail area. We spend more time studying landings on the charts, including alternative points of refuge in our planning and always trying to match the tide and the current. Paying closer attention to weather is another consequence of dealing with a limited range. Even if it would not be our first choice sometimes we have to leave at night or arrive with the dark. In other words, our sailing skill and navigation competence have improved thanks to electric propulsion.

What I am doing today is a sort of a beta test, the science fair version of astrophysics. Considering our limited budget and resources, the results are encouraging and what is really exciting is that there are optimistic signs that this technology will be more and more viable for future use and diffusion in the marine industry.
Even if we are being thrifty, we are aware how our battery bank have a relatively short lifespan. Well cared lead-acid batteries can last 7-10 years but the test of electrical propulsion is a harsh one, that’s why we are doubly careful on how we treat how power reserve
With this in mind, I look forward to what may be available in 2020 in terms of batteries and their cost. The electric car industry, Tesla in primis, has shown the world that the technology is already here and that only scale production and policy are the limits to a wider diffusion. The marine industry is opening up to LiFePo4 technology for power storage, and even if today is still very expensive, there is no need for technological breakthroughs, just a more mature industry and a wider market.
I would use Lifepo4 batteries today if I could afford them. This way I would extend my motoring range by 40% at 50% the weight of my actual setup. In this way I would be less concerned to push down harder on the throttle if I feel like, or worry about the time between full recharges, as lead plate sulfation would not be an issue. I this way I would feel more confident and leave behind our gasoline generator. The much decreased weight would give me better sailing and motoring performance in return. In other words, power will still be “scarce” but less so.

We rarely encounter other cruisers with electric propulsion (but thanks to the internet we met a guru and now we know some others) and we feel that somehow we are an anomaly, especially when it’s a calm day and other vessels motor at full steam, while we bob around with full sails trying to catch any breeze and spending very long time to cover few miles. Sometimes it’s not fun. We are lucky that our sailing doesn’t have to follow a particularly strict schedule, so it’s not dramatic either.
When we purchased our boat the type of auxiliary propulsion was not among the most important criteria in our selection, and the fact that Tranquility came with electric propulsion was somehow a coincidence. We thought that we could any time switch to a different system if we wanted to, but after trying it we got intrigued and realized that even with its limitations electric propulsion works for us.

Today electric propulsion would be my first choice for a sailboat up to 35ft. Its minimum maintenance, the fact that is quiet, reliable and simple and has no fumes from fuel and oil are the perks that balance the labor that takes to sail more, which coincidently is why we are on the water in the first place.

24 thoughts on “One man’s experiment with electric propulsion”

  1. I couldn’t agree more with you. My own system is very similar to yours and 3.75 knots in calm waters gives me 20 nautical miles range from my 200 Ah, 25.6V LIFePO4 bank. I believe I have become a better sailor because of my electric. Sure I could have upped my power and range but mine (like yours) was designed as a sailing auxiliary and that means paying attention to tides, currents, wind, sea conditions and searoom more so than with a diesel designed to punch on reagardless.

    1. Thank you John, I’ve always looked at your systems as an example, and thanks also for all the precious advices you gave me. I am sad to hear that Elektra is for sale, it’s a trustworthy boat and deserves to keep sailing. Well I am sure you are enjoying biking as a good alternative. Myself I think the best form of transportation is walking, cheaper, easier, enjoyable!

      1. Walking is great, if you can. Up to the point I got the bicycle I was still hobbling after a year sitting in a chair. My knee still has problems but as cycling is non load bearing it is much easier than pain when walking. Yes, I don’t really want to sell the boat but health has pushed it that way, so it will be replaced by a 2nd hand motorhome so I can still travel.

        1. Nice plan. Biking is a great way to travel too! I did some cyclo-camping-touring when I was younger, Holland and Denmark amongst others.

          1. Great stuff. Interestingly cycling , subject to speed as it is with walking, can be more efficient in calories used. Regardless with my health issues it works great with the electric assistance and I can choose the power assist level to suit. I’ll not be giving up sailing, just taking on less of a challenge to single handing – so it’ll be the occasional champagne cruise on my friend’s 58′ Discovery instead 😏 Happy sailing Fabio.

  2. I wonder where we’ll be 5 years from now regarding electric engines on boats.
    Given that even today the mainsail can be used as solar panel.

    Over the next 5 years I’ll be preparing a 41″ ketch for a circumnavigation, it will be interesting to so how far this road we’ll be able to go …
    Would be nice not to have to haul 250+ liters of diesel around …

    1. The electric motors will be the same, it is a very old technology that doesn’t need any improvement.
      Batteries are the frontier, especially their cost.
      You’ll have the equivalent weight of fuel in batteries, but a much more lighter motor! In 5 years there should be more options on the market, that’s what I hope because in the same time my batteries will be dead, and I will look for a new bank.
      On a 41′ you should have plenty of surface for solar panels!

    2. I wrote that blog. Solar cloth and solar boom and mast panels are developing well, as are brushless motors with prop regeneration. The best example is probably the Oceanvolt equipped Arcona 380Z.

  3. I sail on a 38ft Kennex catamaran that was converted to electric propulsion in 2010. It is fantastic. With a great battery bank and generator, we have done some awesome sailing with only minimal expense for fuel [for the generator and outboard motor for the dinghy]. Sailed to the Bahamas for 5 weeks in May/June 2015 and 2 weeks in Cuba in May 2016. We removed the propane stove and use electric fry pan. electric pots, electric coffee maker, toaster, etc., for cooking along with a microwave and, of course, a propane grill [which is pretty much mandatory on any boat].

  4. I’m in no way trying to highjack this blog, but there seems to be some very sensible people here that know about EV-boats.
    So if you don’t mind, I’d like to exchange some ideas/possible issues here.
    If not we could take this private (by e-mail).


    1. Hey Jurgen thanks for your concern but I feel that the comments here are the best space to talk about Electric propulsion, so don’t worry about hijacking the blog! I myself as a user of electric propulsion I am very keen in sharing ideas and questions, as I am interested in improving this technology and make it more viable, for a a very selfish point of view. Comments, questions or suggestions are always welcome!

  5. In that case …
    Like you guys I would like my 41′ Ketch (a 1972 Dufour Sortilege, to be precise) to be a testbed for ‘green propulsion’.
    I don’t quite follow Marilyn when she states using electricity for everything aboard, and using a generator to balance the power deficit?
    My idea would be to minimalise electricy use (using leds, ..) and maximize generation in order to be self-sufficient. That is why I’m interested in that solar-cloth…
    Also I would recon there to be a big difference using the same engine on a non-displacement hull (the 38′ cat) versus on a 41′ ketch (8900kg of water displacement)?

    Also I’m wondering what kind of hp engine one would need for such a (heavy) boat, and how about the related batterybank?

    John, what is the problem with the brushed engine and propane gas? Explosion, and it the danger bigger then with a conventional Diesel? (I’m an IT-guy, sorry for my ignorance).
    And how about another fuel source, fi an Origo 6000 burner using denatured alcohol as fuel)?
    And the brushless DC engines you said are being developed would solve this?


    1. Jurgen,

      In the firt instance I suggest you buy this book, which will help with your questions:

      It’s a PDF download and James Lambden knows his stuff from hard won experience. Much of what he has written, I have confirmed with my own conversion.

      The issue with a simple DC brushed motor and gas (we actually call gas petrol in UK so I’ll stick to the word propane) of the propane variety is it is heavier than air so if it sank into the bilge you may not smell it and even if you have a propane alarm sensor (hi and lo level alarms) they can fail – so propane and potential sparks equals a big bang. Hence many use brushless AC motors, but the Lynch design I use which is basically the same as Fabio’s is a well proven design that can run up to high voltages at up to 93% efficiency (7% wasted as heat).

      You mention the Origo and denatured alchol (bio-ethanol) which is in fact what I use, a great stove. I use this fuel:
      Marilyn is talking about AC electricity cooking I think using an induction hob, which is driven from the DC battery voltage via an inverter to create AC. The generator could be DC or AC to charge the batteries. This is how I use my generator, both as a range extender and as a small supply that can also be supplemented by the addition of inverter power for electric cooking etc, so I don’t need to run a generator. I explain it here (I hope!):

    2. Jurgen,

      First I think you should figure out what use of auxiliary propulsion you have in mind. Having previous experience helps, but in my memory when I used to have access to diesel engine, I wouldn’t think twice about turning it on.

      One thing is if you are looking for a system that simply helps you maneuver in tight areas and help you in little waterways transit. Another one is if you are looking for a reliable and powerful motor that pushes you at hull speed for extended time. No amount of solar and wind would be able to guarantee you extended range, so if you want that you should think about a generator to back up the battery bank.

      If you are more on the minimal scenario you have to make sure you would tolerate certain “annoyances” that the modern cruiser don’t want to cope with. Think about a situation where the wind dies and you still have few miles to destination, how would you feel about sitting there and drifting waiting for some breeze, or you have to anchor or heave to and waiting for favorable tide to come into an inlet? Maybe it’s about to get dark, and you know that at your current speed you would get there in the dark.

      For a heavy displacement boat like yours I would think AC three phase motors will be more powerful (and safer compared to DC). That is the same system Tesla uses, through an inverter that converts batteries DC current into AC. I have no first hand experience on this but it’s probably not rocket science.

      The people on UMA that displaces 13,500lbs ( ) have a very minimal system that work for them. They use a 6.3kW DC motor (Tranquility’s 5kW).

      Anyway, before designing the system I think it’s vital that you clarify in your mind what performance you are expecting from your auxiliary. It would make for very different scenarios and budgets.

  6. The closest thing I have seen to ‘our’ boat would be

    I have been a racing IOR halfton yachts most of the time since I picked up sailing, so I think I could do with waiting a little. Mostly I see an engine as something that is used for manoeuvering in a marina, besides that it gets little use.

    Considering that most of the path we’ll be following for that circumnavigation is going to be the tradewind route (with a couple of deviations), and hopefully some extended periods that we won’t need the engine, I’m still wondering if it can’t be done with an oversized batterybank.
    I’ll need to look up the numbers and do the math, but I think it will be an interesting exercise.

    Oh BTW, I’m no fanatic! I never said that I absolutely refuse to take a generator, but I believe more in conserving electricity by using other sources of fuel for cooking (like the bio-ethanol) or even marine power cells ( for
    power generation …


  7. I appreciate all the information shared here. I’m currently looking at a 1985 Hunter 33 that I can buy for less than $8K. It floats. It has a leak or possibly 2 from the short visit I had onboard the day during rains. There’s also stuff like a plotter, older vhf radio, alcohol stove….
    The one thing that stands out though is the Thunderstruck 10kW electric motor and parts he ordered but never installed.
    It all sits in 2 boxes in the empty motor compartment (removed the original motor for this project).
    The boat will come with an outboard.
    Taking this idea to online sailing forums brings back an almost unanimous, “WALK AWAY NOW!” type of attitude.
    Partly because of concerns of what I might find after buying the boat and hauling it out… mostly due to the uninstalled ELECTRIC motor.
    I am comfortable doing electrical work on houses, small electronic projects, and even replacing the large traction battery on my Prius.
    From everything I saw on Thunderstruck’s web page, and from the experiences you all are providing here (as well as details of your own installs), I’m thinking this ‘project’ boat might be a doable thing without too much pain!
    Thank you again for sharing your information as well as links. I’m checking it all out! 🙂

    1. You are welcome! I would say focus on the sailboat and not on the propulsion system. You can change the propulsion system anytime but you can’t modify a hull. Make sure the boat you buy is manovrable and sail decently because you will have to sail more with an electric propulsion.

      1. Thank you for your reply. I agree with how the boat sails and also what structural shape it is in.
        I’m taking several months and many hours pouring over as much information as I can find on different boats. I have been thinking a lot about the purpose I intend for my future boat. Price started out as the top factor, but has slid down as I gain experience in boat shopping, with helpful advice from many on the subject! 🙂
        For the Hunter 28.5, the big question was about the motor issue. I started away from it purely due to the need to install an electric propulsion system I had no experience with. But reassessing my use for the boat, what instances I feel I would need the auxiliary power of a motor, and educating myself further on the electronics world (thanks again to your blog and videos), this boat is back in the running.
        Still more to learn and more boats to look at before the final decision is made and a commitment taken! 🙂

        1. The electric motor, especially if it is a DC setup, it’s not a complicated installation.

          Good luck with your boat quest!!

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