I live on a small sailboat with electric motor as auxiliary power, and even if this happened by accident, I decided to try out this technology as a total novice. Five years and 6000 miles later I describe my experience in this post, trying to draw a general picture of the use of electric motors aboard small sailboats.

Electric vehicles (EV) and hybrids are conquering little by little the market of light duty vehicles, 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”.

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 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 clear that the diesel option dominates the market on sailboats auxiliary propulsion. In fact, before owning a boat with electric propulsion, my only experience was with diesel engines and, less often, gasoline outboards.

THE DIESEL BIAS
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 power to face many difficult situations and emergencies.

When I first encountered electric propulsion it was a quirky novelty, something I was not prepared to deal with. I was reluctant, but I knew that if I was not happy with it, I could easily revert to ICE. It was hard to find good information on the topic, so I guess the only way to know was to run the experiment myself.

One of the common temptations is to approach the topic trying to answer the question if electric propulsion can replace the diesel engine. After all why choosing an option that cannot compete with the market leader? After a lot of research, re-doing myself the installation of my electric motor, and using it for more than 2000 nautical miles, I finally have an answer.
Electric propulsion can’t replace the diesel engine. What it did for me was to change the way I see and use auxiliary propulsion.

A DIFFERENT MINDSET
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 few seconds 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. 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.

ANATOMY OF OUR “LOW COST” SYSTEM
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 5kW (6 h.p.). It is compact in size 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 reasons behind the choice of a “traditional” lead acid 6v battery are 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 the manufacturers of a “rare” battery, 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.

When we are drawing more than 20 amps it’s because we are fighting headwinds, currents in a narrow passage or performing a maneuver that requires high thrust, situations that should not last long if we plan our sail wisely and that does 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.

OUR TESTING GROUNDS
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. Our priority was to get south as fast as we could, without taking the risk of rounding Cape Hatteras during winter.

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 possibly 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.

During the rest of the trip we sailed and motor-sailed along portions of “the ditch”, but making most of our miles offshore picking good weather windows. 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.

THE ART OF COMPROMISE

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 makes it necessary 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 these 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 MAKES BETTER SAILORS

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). Because of our limited power, we purchased bigger nylon 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.

FUTURE DEVELOPMENTS

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 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 extremely careful on how we treat our power storage.

With this in mind, I look forward to what may be available in 2020 in terms of batteries cost for a sailboat with electric motor. 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 setupand 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.

With Lifepo4 batteries 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.

A SMALL MINORITY

We rarely encounter another sailboat with electric motor (but thanks to the internet we met a guru and now we know some others) and we feel like 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, and we wished we had a diesel engine. We are also 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. We were pleased by her sound hull and the solid rig, we loved the interior and other features. The fact that Tranquility came with electric propulsion was somehow a coincidence. We thought that we could switch to a different system if we wanted to, and 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.