Electric Propulsion

Electric Outboards, are they worth it?

Electric propulsion is growing in popularity! A few years back, the thought of something being powered by an electric motor was just a distant dream.

I remember when our school was “visited by an electric car.” The engineering department at the local university put a considerable amount of focus and effort into creating an electric vehicle. This car was something out of a science fiction movie, with everything being ultra sleek and efficient in an attempt to barely meet the minimum standards of what a normal citizen would consider to be a “car”!

Jump forward a few years and electric cars are common place on streets and parking lots. They no longer draw a crowd around them when they appear, as they have become somewhat accepted and commonplace.

The same seems to have occurred in the marine environment. Boats are being powered by electric motors instead of by an internal combustion engine. Large boats have inboard electric motors, and their dinghies are being fitted with electric outboard motors.

When it comes to propulsion for your dinghy, is it worth the upgrade to electric? Well, it depends on what you want.

The most prominent and trusted brand in electric outboard motors is Torqeedo. They are the motor that people picture when they are talking to someone about electric outboards. This is because Torqeedo made the perfect electric outboard.

The battery is included in the motor assembly, so it looks like a clean installation. Then they made the battery information clear and easy to understand! When you are motoring along, it tells you how long you can sustain this speed and how many miles you can go at this speed. This made it easy for people to realize and understand that you can’t go full power all the time! The faster you go, the shorter a distance you can motor. The slower you go, the farther you can go on a single charge.

So, what are the great advantages to a Torqeedo motor? Well, first of all, the thing is silent! The motor is powered by electricity, not thousands of explosions per minute. This means that the motor will be silent when you are coming in to dock, which makes it easy to communicate with people in the boat with you as well as those on shore. How often is it that someone is trying to tell you something but you can’t hear them because you are sitting right next to the noisy outboard? That problem disappears!

The drawback to this very green situation is that the motor runs on electricity and that power won’t just fall out of the sky! Or will it? Charging the battery is a slow process. If you have the time and enough solar panels, you can easily charge the battery with the sun, which does mean that power is falling from the sky. Charging the battery up is going to take a few hours, whether you have a giant solar array and all the sun in the world, or if you are plugged in to a generator. Charging takes time and that time means that you can’t use the outboard while the charging is taking place.

I had the opportunity to speak with the Torqeedo representative at the Annapolis Boat Show in 2018, and he said that the outboard will charge overnight when plugged into the mother ship. This is fine, but the problem of generating the power just got shifted over to the main boat.

In our opinion, the boat or the dinghy can be electric, but not both. We have an electric motor in our sailboat, and therefore can't run our motor to generate the power to charge the outboards’ battery; we already need that power for the boats battery bank! We rely on solar power to charge up the boats batteries, and barely have enough for that task, throwing in the need to charge another battery is simply out of the question.

We find that when we anchor somewhere, we then motor around in the dinghy to get to different beaches, snorkeling spots, or shore. We have to be conservative with our motoring when on the boat, since we have limited range with our electric motor, and the thought of having to be equally conservative in the dinghy would get old really fast!

Sometimes, we feel like we are putting on a show in the anchorage, as we will go between shore and our boat a few times before we actually “go to shore.” This is because we may have forgotten something and need to return to the boat to fetch it before we go. With an electric outboard, these “whoops I forgot something” trips might be too much and consume your range too quickly. We also do a fair amount of exploring by dinghy, going into uncharted waterways where we can explore. Having the worry of range will quickly take away from the carefree joy that comes from exploring new mangrove canals in an island you just landed on.

For these reasons, we have a gasoline outboard which we use on our dinghy. We have a 2hp Honda air cooled outboard, because it is light enough that I can carry it in one hand, which makes mounting it on the dinghy even easier, and it has an internal gas tank that holds a quart of fuel.

The setup is just as clean of an installation as the Torqeedo, and the range is probably also very similar, but the charge time is where the Honda runs ahead of the Torqeedo.

Since the fuel tank is 1 quart, we simply carry a 1 quart mason jar of gasoline in the dinghy, along with a funnel. Should we find ourselves low or out of fuel, all we need to do is decant the jar of gasoline into the outboard motor, then we can fire back up and continue on our way. Technically, that was the recharge phase which would take the Torqeedo hours to complete.

The Honda is much louder, and you can’t really have a conversation in the boat while motoring, but you will get there faster than rowing, and you can carry an entire “tank of fuel” with you.

We feel that if you have an electric motor on your boat, maybe a gasoline outboard would be a good idea over an electric outboard. This is because charging is the biggest hurdle to overcome with electric motors, as the power has to come from somewhere and if the sun isn’t power the solar panels and the wind isn’t powering the wind generator, you will need to fall back on fossil fuels for electrical production.

If you have an internal combustion motor in your boat, then you can generate the power needed for the outboard motor’s charging, and suddenly, the thought of producing power for the outboard’s battery doesn’t seem like such a stressful point!

So, if your boat is electric, consider a gasoline outboard for your dinghy.
If your boat is not electric, an electric outboard would be a fun way to enjoy the joys of electric propulsion while still having a reliable source of electricity for the charging times.

Watts, Volts, and Amps

Batteries, Electric Motors, Solar Panels, Generators, and Wind Generators all have one thing in common, their outputs are typically measured in Watts?

Why watts and not amps or volts? Well, the answer is actually rather simple: watts don’t change depending on your setup.

You see, Watts, Volts, and Amps are linked in a mathematical formula. W = V x A

From this formula, you can determine the third value when you are only given 2 of the values by way of simple algebra (and you thought you would never need to use it again)

To not bore you with math, I will surmise to say that as volts and amps fluctuate inversely to each other (as volts climb by a factor, amps decrease by the same factor) watts remain unchanged!

For example (I couldn’t resist):

100W = 12 volts x 8.333 amps
100W = 24 volts x 4.166 amps
100W = 48 volts x 2.08 amps

So, when you purchase an electrical device, they can simply tell you how many Watts it produces or consumes, and the way you wire it will determine the voltage and amperage that it will operate.

To take this further, with electric propulsion, you will see the motors listed in the form of kW instead of Horsepower. The reason is the same, as the motors can come in a whole range of voltages, as low as 24 volts and well up over 96 volts! By listing the motors output in kW, they are uniform and comparable.

For example, a 48v motor that is rated at 20kW will draw 416.6 amps at full throttle. A 96v motor that is rated at 20kW will only draw 208.3 amps. In the end, it is the same amount of power being moved, just at different voltages and amperages.

So remember, next time you look at an electrical gizmo for your boat, consider rating it in watts to compare one device to another instead of looking at the amps it produces or consumes; you might get tricked up by the voltages. Then you can compare the cost of these items with the watts they produce or consume and spend your money in the most effective way to get as many Watts as you can out of each dollar.

Electric Motor Regen

It seems that little is ever truly discussed about regenerative capabilities (or regen) of an electric motor on a yacht. Those who don’t have electric motors often tout that regen is fictitious and doesn’t actually produce any usable power, while those with electric motors seem to keep quiet about it.

I wish to break that silence and go into the details of regen and what it can actually do.

Regen occurs when you are sailing and the force of the water over the propeller causes the propeller to spin. Since the propeller is connected to the motor, the motor will also spin. With a small electrical current supplied to the motor, the magnets in the motor will begin to act as a generator and produce power that will feed back into the battery bank. This process can add a lot of power to your batteries, giving you more range under power later while also supplying power to run your yachts electrical systems.

But how does it do this and how does regen work exactly? Regeneration is the transformation of kinetic energy into electrical energy. This takes work to accomplish, and leverage really helps here.

The magnet inside the electric motor is resisting movement thanks to the electromagnetic field created by supplying a small amount of electricity to the wires that are wound up around the motor. To make the magnet spin, you need enough torque on the shaft (work supplied by the propeller) to overpower the force of the electric field and cause the magnet to rotate. You also need the magnet to spin quickly to pull the electrons in the field around fast enough to create a flow of electricity. So, you need fast spinning and you need lots of torque.

As you can imagine, it all comes down to the propeller, as this is the structure that is going to create the spin and supply the needed torque to the motor. The more blades your propeller has, the more effective it will be at being turned by passing water. Also, the longer the blades are (larger diameter of the propeller), the more torque can be generated.

Imagine that you are trying to change a tire and the lug nuts just wont budge. You are faced with two options: get stronger or get a longer wrench.

Getting stronger will apply more force to the same wrench which will then supply enough torque to the suborn lug nut and remove it. This is the equivalent to sailing faster to cause more water to rush by the propeller and force it to spin.

Getting a longer wrench allows you to multiply your force thanks to leverage which will supply more torque to the stubborn lug nut while you are still applying the same amount of force on the wrench. This is the concept behind “foot pounds”. If you hang 1 pound from a 1 foot wrench, you would be exerting 1 foot pound on that stubborn lug nut. But if you hang that same 1 pound from a 2 foot wrench, you would now be exerting 2 foot pounds on that same lug nut!

Having a larger diameter propeller means that the force of the water at the tips of the propeller blades will have much more leverage and will generate much more torque. This will allow you to spin the magnet in the motor with more torque which will in turn generate much more power than if you had a small propeller which supplied much less torque.

Sadly, due to clearance issues, it is impossible to simply “make the propeller huge” on a yacht, as you are limited by the space and clearance of the hull structures around your propeller.

It seems that the minimum propeller size to generate any appreciable regen is 16 inches. Larger propellers produce more torque and therefore can generate much more regen power, while smaller propellers don’t seem to have enough torque to overcome the electromagnetic field of the motor and generate sufficient amounts of power.

This is where the bad reputation gets further muddied. Smaller yachts that are used as day sailors tend to also have small propellers, so they are not being used for long enough distances and have propellers that are too small for the task at hand. Larger yachts have larger propellers and are often cruised over long distances. There are many more day sailors than there are blue water cruisers, so the number of stories of “it doesn’t work” vs “it works great” gets skewed.

I feel the best way to look at regen is not to view it as instant power being added back into your batteries, but more in the view of power that can be harvested over a distance that is sailed. Regen needs a few key ingredients to work, you need a large propeller with many blades and you need speed. We are equipped with a 16 inch diameter three blade propeller, which apparently is the smallest size and number of blades to get any appreciable regen from, and are able to generate around 2 amps @48v while sailing at 5 knots, and 6 amps @48v when sailing at 6 to 7 knots. We never seem to sustain speeds of 8 or 9 knots for a long enough time to retrieve the really high amps that are being produced, so for all intents and purposes, I ignore them.  If we are sailing at speeds less than 5 knots, regen is insignificant and we actually turn the system off so that the propeller can free wheel without slowing us down much. 

So, imagine that we are sailing along at 5 knots and producing 2 amps @48v. This means that in 1 hour, we would have sailed 5 nautical miles and generated 2 amps @48v. If we sail at this speed for 10 hours, we would cover 50 nautical miles and generate 20 amps @48v (or 80 amps @12v). At the same time, if we managed to sail at 7 knot for that same distance, you would only sail for 7.1 hours but have produced 42.8 amps @48v (or 171.2 amps @12v) in that same distance! As you move faster through the water, you will spin the propeller more quickly and that will generate much more power; but you do have to sail the distance to extract the power for your batteries. 

Nighttime photo of motor display while sailing between 6 and 7 knots.

Nighttime photo of motor display while sailing between 6 and 7 knots.

In the display above, you can see that it is producing 6.0 amps at 51.22 volts DC, and 0.30 kilowatts because the motor is spinning at 247 revolutions per minute.

What this all means is that our electric motor is producing 300 watts of power and that power is being fed back into our batteries. 6 amps might not sound like much, but this is in a 48 volt system. When the power is stepped down to 12 volts to power the yachts electrical systems, those 6 amps are the equivalent of 24 amps in 12 volt!

Suddenly, the tiny electric motor is producing the same amount of power as three 100 watt solar panels, but this is occurring all the time! It can be high noon on a cloudy day, or in the middle of the night, the motor will produce this kind of power when you are sailing through the water with enough speed to turn the propeller.

So, why is regen not typically talked about? Well, the numbers are not representative of what you are getting at every single moment, but more of what you could get in an hour. People like instant results and don’t want to wait around for it, but they don’t seem to realize that they have to wait for everything anyways. Solar panels take hours to charge batteries, and so do generators, but these are things that people usually set and forget. Regen requires the boat to constantly remain in motion and if your speed falters, so will your power production. If you are hand steering, then you are going to have to work for that power! If you have a balanced sail plan and wind steering, then it becomes just as passive as your solar panels, wind gen, or genset.

In this example, 300 watts added to the battery bank would only be there after a full hour at this speed. If you are puttering around for a few hours, 300 watts per hour might not add up to anything appreciable, which is why regen has gotten a bad reputation. When you are passage making and sailing around the clock for days, these numbers become very real and very important.

Hour: Watts / Amps @12v / Amps at 48v

1: 300W / 24 amps / 6 amps

2: 600W / 48 amps / 12 amps

3: 900W / 72 amps / 18 amps

4: 1200W / 96 amps / 24 amps

5: 1500W / 120 amps / 30 amps

6: 1800W / 144 amps / 36 amps

7: 2100W / 168 amps / 42 amps

8: 2400W / 192 amps / 48 amps

9: 2700W / 216 amps / 54 amps

10: 3000W / 240 amps / 60 amps

11: 3300W / 264 amps / 66 amps

12: 3600W / 288 amps / 72 amps

13: 3900W / 312 amps / 78 amps

14: 4200W / 336 amps / 84 amps

15: 4500w / 360 amps / 90 amps

16: 4800W / 384 amps / 96 amps

17: 5100W / 408 amps / 102 amps

18: 5400W / 432 amps / 108 amps

19: 5700W / 456 amps / 114 amps

20: 6000W / 480 amps / 120 amps

21: 6300W / 504 amps / 126 amps

22: 6600W / 528 amps / 132 amps

23: 6900W / 552 amps / 138 amps

24: 7200W / 576 amps / 144 amps

300 watts per hour tallies up in the table.

What this means is that if you only sail at 6 to 7 knots for a few hours, you will only gain a few hundred watts, just the same as you would produce from a 300W solar array in peak sunlight hours. This will give you a few watts to play with here and there but probably nothing you would really notice.

If you go out for a daysail and plan on having the regen charge you back up to bring you back into port, but you only sailed for 2 hours, you can only expect to see up to 12 additional amps in your motor battery bank if you managed to sail at speeds over 6 knots for the entire time. This is really insignificant and probably where the bad reputation comes from.

When you are sailing a long distance, and are under sail at speeds over 6 knots for around 12 hours, you could expect to see up to an extra 72 amps in your motor bank! This is a significant amount and will provide you with the power needed to bring your yacht back into port with ease.

When we were crossing the ocean, we were sailing for days (almost a month actually) and we had full batteries the entire way!

Our motor bank is 210 amp hours @ 48 volts and our house bank is 525 amp hours @ 12 volts.

If we left port with completely empty batteries (which was not the case) we would have been able to charge the house bank fully in 22 hours, and have the motor bank completely charged in the next 35 hours! This means that in 57 hours, we could fully charge all of our batteries without using a single drop of fossil fuels; just by sailing fast!

In our case, we actually left with full batteries, but all of our electronics needed lots of power on the crossing, and they were all supplied completely by the regen of the electric motor.

Now, not all electric motors have regen, so it is imperative that you make sure the one you are looking at does. Our electric motor is a QT20 (Quiet Torque 20kw) from Electric Yachts

This motor is a plug and play design, allowing you to have all the benefits of a well engineered system that simply drops into your boat. It gives you all the information you need to properly operate it while maximizing your range and motoring time. It also has a very simple user interface to set the regen level you desire. When we were looking for which type of electric motor to use, we noticed that many of them had complicated procedures to regen, and some of them could easily begin to draw power if you were not paying close attention! This one is pretty much fool proof, as regen occurs when the throttle lever is in the neutral position and power consumption occurs when you move the throttle lever forwards or backwards.

Regen is a truly remarkable feature of an electric motor which I feel makes it the best motor to have for blue water passage making. If you are a coastal cruiser who only does short trips, regen might not be very apparent to you, but the moment you head out on your first long leg, regen can keep you charged up.

Upgrading to Lithium Batteries, Battle Born vs. Renogy

Electric motors are great, they have few moving parts to maintain or fail, and they can run effortlessly forever…or until the power runs out!

The heart of an electric setup is not the motor, but actually the batteries. These boxes of energy house the electricity that the electric motor needs to propel your yacht. The more power you can carry in your batteries, the more power you can use with your motor.

When we did our conversion to electric propulsion back in 2014, we chose AGM batteries, simply because they were the most cost effective at the time. They provided us with a lot of power in a large space and required little maintenance.

Fast forward to the present, and our AGMs are old and outdated. Better battery technology has come down in price and the “better batteries” of 2014 are no longer prohibitively expensive.

At the moment, there are two companies that seem to be reigning as king over the “direct replacement” lithium batteries. These companies sell lithium batteries that are the same size as the more popular lead acid and AGM batteries, but at a fraction of the weight.

The first company is Battle Born

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Source: https://amzn.to/2TfdpoP

These batteries are the same size as a Group 27, but contain the power of a Group 31. Moreover, they only weigh 31 pounds! Our current AGMs are Group 31 and weigh 67 pounds each, meaning these batteries weigh less than half of what our batteries weigh.

The next battery company that we will look at is Renogy.

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Source: https://amzn.to/2TgtLO3

Renogy Batteries are also direct replacements for lead acid and AGM batteries, but these are even lighter in weight! Their 100ah battery weighs in at only 28 pounds!

Now that we know the major players in “direct replacement” batteries, lets look at why they are more sought after than a regular lithium battery. The first thing is familiarity. For our entire lives, batteries have been this rectangular box that sits in our boat or car and has two terminals on it. Lithium batteries can come in a huge variety of shapes and sizes, which sadly leads to people wondering “which side is the top?” Direct replacement batteries do away with this metal block to lithium by packing it into a familiar shape and size.

The second advantage comes with the voltage. Lithium batteries are made up of cells, and the entire battery pack can have any voltage value you want! This once again becomes a problem since people are used to a battery being 12 volt. In our case where we run a 48v motor, we simply have four 12 volt batteries hooked up in series to create the 48 volts we need to operate. Instead of Battle Born and Renogy offering their batteries in “custom voltages” they packaged them as 12 volt batteries.

You might be wondering, why switch to lithium at all if they take up practically the same space and give you the same amount of power? There are two answers to this question. The first is weight, and the second is usable power.

Lithium batteries weigh less than half of a regular battery. The best way to visualize this is to look at the Amps per Pound at 12 volts.

AGM batteries hold 105 amp hours and weigh 67 pounds
This is to say 1.567 amps per pound

If you want to have a 800 amp hour battery bank, it will weigh (800/1.567) 510.5 pounds.

Battle Born batteries hold 100 amps and weigh 31 pounds.
This is to say 3.225 amps per pound

That same 800 amp hour battery bank would now only weigh (800/3.225) 248 pounds

Renogy batteries, being the lightest, hold 100 amps and weigh 28 pounds
This is to say 3.571 amps per pound

The same 800 amp hour battery bank would weigh just a smidge less at (800/3.571) 224.0 pounds.

So, you might be wondering now, aside from weighing half as much, why bother with expensive batteries? They take up about the same space, and if the boat isn’t overloaded, why bother? Well the truth is, all batteries hold power, but they don’t all let go of the power the same.

Think of batteries as a jar of jelly. They all hold the same amount of jelly, but they differ in how the jar opens.
Lead Acid and AGM batteries have a small opening at the top of the jar, so you can get your spoon straight in, but you can’t get to the sides of the jar. When you have gotten all the jelly you can reach, you notice that there is still a lot of jelly left on the sides, but you just can’t seem to get to it!
Lithium batteries have a much larger opening at the top, so you can get to the sides of the jar much more easily. This lets you get to more jelly and leave the jar more empty when you are finished.

Lead Acid and AGMs can safely discharge down to 40%, while Lithium batteries can safely discharge down to 10%. This means that in a 100 amp hour battery, an AGM can give up 60 amps while a Lithium can give up 90 amps.

So, back to our hypothetical 800 amp hour battery bank, made up of eight 12 volt batteries. The batteries sitting in their box hold 800 amps hours. If these batteries are AGM or Lead acid, they could only give out about 480 amp hours. This identical battery bank made of Lithium batteries could now give out 720 amp hours. That’s an additional 50%, from half the weight!

So, bringing the battery bank and electric motor out of the hypothetical realm and into reality:


Our electric motor draws from our battery bank composed of eight AGM Group 31 batteries, each with 105 amp hours. We can motor at a slow speed of 2 knots for about 20 hours, giving us a range of 40 miles. With a Lithium bank, we would be able to motor 60 miles! That might not sound like much, but that is a lot of miles from the same size of battery bank. Yes, more batteries would give more miles, but space is an issue on a sailboat.

The switch to Lithium will be coming, and we will then be able to compare lithium batteries to AGM in terms of usability and performance.

Electric Motor Regeneration

Electric motors have one key advantage over a diesel when it comes to blue water cruising: regeneration.

It is common practice to run your diesel motor once or twice a day to "charge up the batteries" while crossing an ocean. The winds are consistent offshore, so you don't need the motor for propulsion, but you do need the motor for power. 

Imagine being out on a gorgeous day of sailing and then have to crank on your motor for a few hours. All the peace and tranquility is ruined as your diesel clanks and clunks away, shaking the boat and your eardrums for hours!

Electric motors can not be "run" to make power. Running them actually consumes power! The only way an electric motor will produce power is if you are sailing fast enough that the water passing over the propeller actually causes the propeller to spin. This in turn spins the electric motor and causes the motor to act more as a generator, producing power that is then fed back into your battery bank.


There is no need to tarnish your perfect sailing day with a noisy diesel motor. The propeller is spinning all the time and producing power that keeps all your batteries topped off! In this particular moment, we were sailing along at around 7 to 8 knots and the motor was constantly producing between 6.0 amps and 6.9 amps. That might not sound like much until you recognize the fact that this in in 48V. When this is stepped down to 12V, the amps are multiplied by a factor of 4. This means that 6.0 amps @ 48V becomes 24 amps @ 12V and 6.9 amps @ 48V becomes 27.6 amps @ 12V!

Imagine having a quiet source of power that cranks out 24 amps continuously, day and night! Needless to say, we had no issues with power demands while we crossed the Atlantic in the summer of 2018, all without the need for a noisy diesel motor.