The Offshore Voyaging Reference Site

Electric or Diesel-Electric Drives for Voyaging Boats

Solar Panels charging batteries aboard sail boat

Until a few years ago, I thought that diesel-electric would become a viable alternative for voyaging sailboats that would solve the age-old problem of matching the output of an engine to the power requirements of a propeller across a wide range of RPM settings.

But it turns out that this is a more complex subject than it appears at first look.

Let’s examine the viability of electric and diesel-electric drives for voyaging sailboats.

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More Articles From Electric and Hybrid Diesel-Electric For Cruising Boats:

  1. When Electric Drive Works For a Cruising Sailboat
  2. Electric or Diesel-Electric Drives for Voyaging Boats
  3. Real Numbers For Electric And Diesel-Electric Drives
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Rob Withers

Just Like your 5 points of ‘What Really Matters’, the beauty of diesel engines (at least the older ones) is they only need the following to keep going:
– fuel
– air
– some oil
– not much else
On my car, almost invariably the bits that go wrong are bits that weren’t invented 20 years ago. The engine on my boat is 20 years old, so that eliminates a whole heap of trouble!

The gains for a hybrid approach would have to huge to justify the increased complexity.

C. Dan

It is no-doubt due to my own ignorance, but your comments on the “simplicity” of a diesel system made me chuckle.

Check out Tim Lackey’s build-log of his 30′ motor-sailor refit, and you will see why I had that reaction – the photos of the electrical system and engine-room (including a “simple” diesel) make me shrink with terror (as I would have no idea how to fix any part of the system that failed):

Ben Campbell

Do you have thoughts about a pure diesel/electric design—that is, like a series hybrid without huge battery bank? Seems like there could be some pure layout advantages, due to the inconvenient locations conventional sailboats need to put the engine. I’d love to keep the diesel engine out of the living space. It’s noisy and smelly. It’s often a cramped space for something that needs regular access for maintenance.

Gene Gruender

Hydraulic is what your talking about. Diesel motor mounted anywhere, a pump on the motor, a hydraulic motor on the propshaft. Less efficient than direct drive, more effecient and less dangerous than diesel generator and electric motor.

I can tell you from experience, a busted line or seal is a mess, as well as leaving you dead in the water.

C. Dan

Thanks John as always for a thoughtful (and comprehensive!) post on a subject I care about
One comment: Anyone who has a bow-thruster or an electric windlass is already using a series-hybrid electric system – these applications satisfy Eric’s “peaking” requirement (and for those who view an engine primarily as a tool for maneuvering around anchorages, hybrid-electric propulsion could also make sense, as you point out)
And a (loaded) question: Would you agree that technological breakthroughs are more likely to make hybrid-electric (or full-electric) more viable in the future, vs. ICE solutions? There are countless research teams working on solutions to develop better and cheaper batteries, and the same goes for solar panels (which have already seen significant price improvements in the last 2 years).
Note: I am not suggesting hybrid-electric or electric-only for the A-40 (although if an engine-less option were offered, I might take it)

C. Dan

I have read Calder’s work as well, and I don’t think we’ll be able to get away from having something flammable on board (be it solid, liquid, or gas).

I think any of these systems can be designed safely, and any of them can fail spectacularly if they are not maintained properly. I feel like you choose to emphasize the risks of some technologies while minimizing the risks in others, perhaps because you are more familiar with one particular type of system.

Simon Wirth

Hei John
In some cases it is a good thing that hydrogen is lighter than air.
But then, the hydrogen atoms are that smal that there is no way to completly contain it as a gas for long. If there is hydrogen as a gas in the tank, and there always will be, there is hydrogen leaking around. Garanteeing a good enough vertilation may not allways be easy or sage in itself.

John Rushworth


It is interesting that you post this today of all days. Today my boat (SY ELEKTRA) passed her MCA survey, becoming the UK’s very first commercially coded pure electric propulsion sailing yacht, under MGN 280.

As I have said before I think your choice of propulsion for the Adventure 40 is the right one and like you I advocate keeping things simple. More on that in a moment.

Your post whilst biased if you like, in favour (and naturally so) of your criteria for the Adventure 40 is fine for that puprose, but will not suit all types of sailor. Your most telling comment is “it depends what you want”.

It is on that basis that I started my project a year ago. Tommorrow is launch day and time will tell how my ‘electric’ choices stack up against the 10hp 2 cylinder Volvo Penta with 2.4:1 reduction box, compared to my non geared direct electric drive replacement.

In my case capital cost was an issue and my conversion has come out cheaper than a re-engine and likely cheaper than a complete diesel engine re-build, both of those options based on an expected life of around 15 years before accumulative major costs kick in.

So why did I chooose electric? Going on your post it would appear madness to go that route. And the truth is you simply cannot in terms of volume, weight and calorific value beat a good old fossil fuel and the bang for your buck contained therein.

I did the sums, yet still went the electric route. Although as a marine engineer I have the skills and knowledge to strip and re-build a diesel I do not have the workshop facilities and machines to do that. I also like to do it all myself. To convert to electric propulsion (apart from the shipping of the 2 x 8D AGM batteries) I have done the whole conversion, using off the shelf parts, using public transport (I have no car or motorcycle so have used the bus) and a small Musto shoulder bag. The electric system is far simpler to install. I also plan on gaining peace from noise (for the duration of the battery charge) compared to a diesel before I re-charge using fossil generated fuels either at a marina or by using a small hand portable Honda petrol generator and/or using that wee generator (500 Watts) as effectively a serial hybrid. Solar and wind and the pay back time don’t make sense for my kind of sailing at present, which is UK coastal to offshore based, with rarely a non stop passage greater than 100 nautical miles and no plans to be out in anything above a F6.

I’m also not in a hurry so I can wait for wind and if required a re-charge. I plan to sail more and motor less. Rather than go anymore deeply into this, I would also like to add that I think Eric’s comments are if you like made in isolation of other factors, as I have seen no discussion of duty cycle/engine run times and overall efficiency comparisons. Suffice to say I’ve put my money where my mouth is and by the end of this season I hope to show that I have made a wise, long term choice that is kinder to the planet in terms of life time costs and carbon footprint, with (and you can laugh now) a future option to not sail and wait the 7 to 10 days it would take to re-charge my batteries using wind/solar, when I can afford them. Indeed some folks can do that as their boat sits on a mooring waiting for their next fortnightly trip, but with no use of fossil fuel to re-charge.

On that point I’m glad to see your post and your desire for future, more eco conscious choices. In closing all I can say at this point is I started with steam, have done diesel and when I have quantifiable real world practical data, I will have done electric. The proof of the pudding is in the eating. Someone has to taste it before the rest of you and the taste won’t be for all. Time will tell.

In the meantime here is my finished conversion on a public Facebook diary page.

John Rushworth

Brilliant John. How about this Totaly agree re ‘green’. It is a word I am carefully avoiding. I don’t know of any UK renewable energy marinas. I think it will happen, but not as long as business sells fossil fuel generated electricity at affordable prices. My electric drive is a scoot home one with a bit of added ooommf and battery time to get off a lee shore. I best shut up now till I’ve sailed her – this weekend for the first time!


Hi John,
Actually if you look at the whole system analysis for an all-electric plug in car running off a grid powered by coal you will find that it is still far more efficient and emits less Co2 than the same vehicle powered by diesel or gasoline.

RDE (Richard Elder)

Hi John,
Here is the original study from a number of years back that I based my comments upon. I doubt that it represents the whole story.

Problem is, no government, and certainly no energy minister or corporation is willing to even try to estimate the real cost/benefit/risk analysis of a particular form of energy use and production. Business as usual and short term profit maximization are the only points of reference.

If you want to estimate the real cost of a gallon of gasoline used in the US to take the kids to soccer practice, you have to include the cost of fighting an endless series of wars in the Middle East to maintain control of the world’s largest and cheapest sources of oil. Ex CIA director James Woolsey put the real cost of gasoline int the US at $12 per gallon several years ago, and that didn’t even begin to estimate the potential economic cost of Co2 causing radical climate change.

So the “numbers” are much more complex than mere conversion and thermal efficiency studies would lead one to conclude.

Matt Marsh

The Tesla Motors article makes some valid points, but at first glance I do see one critical point they’ve biased in their own favour: They assumed that the electric car was being charged by a GE H-System gas turbine at 60% thermal efficiency.
Very few such power plants exist, and the ones that do exist are used mainly to handle peak loads when demand is high and other generators are maxed out. You need to cut that figure in half if you’re getting your power from a 1960s coal station, in which case the $109,000 Tesla isn’t much better than the ’93 Civic.
On the flip side, in Ontario you could charge the electric car at off-peak hours when, thanks to nuclear plants (which produce a constant power output 24/7) and hydro dams, electricity generation is cheap and nearly carbon-free.

But then we move to the marine case, and the electric car’s single biggest advantage- its regenerative braking- no longer applies. To get any decent range calls for obscene amounts of battery, and until we make another order-of-magnitude leap in energy density, that just isn’t going to fly outside of specialty applications.

You wouldn’t use Pb-acid batteries for an all-electric boat, of course, but the alternatives are still too expensive and not powerful enough. That will change, in time, but we aren’t there just yet.

John Rushworth


One further thought on what we are doing to the planet etc. Have you considered approaching Dame Ellen Macarthur ref her new project in considering your design, build, lifecycle of an Adventure 40? This explains matters well! Her website is here and her ideas are starting to gain traction.


Hi John,
The problem with setting up a straw man and then knocking it down like Eric does is that one tends to get straw all over you. You lost me when you started talking about a forty eight 8-D battery bank or 450 SQ FT. solar array.

A statement like “Hybrids are very hard to justify in sailboats in my opinion as they lack any real advantages —” simply tells me that they haven’t considered or experienced them.

I spent two weeks cruising in the outer Exumas on a boat that closely approximates the power requirements of the A-40. It was one of the earliest attempts at an electric drive system and to my way of thinking far from adequate. That said if an electric drive system met three criteria I would personally choose it for my A-40.
1- My intention was to use it primarily in Caribbean conditions where both sun and wind are the rule.
2- The cost was within 10% of a standard diesel propulsion system.
3- The system chosen had at least 25,000 hours of proven operational functionality in a fleet of boats.

Rather than engaging in theoretical speculation, lets look at an existing real world drive system suitable for the A-40. The 10 KW continuous- 18KW peak water cooled drive motor and 14kw DC generator unit. List price: $29,464 USD

Add two 200w solar panels that will fit comfortably on a bimini, two KISS wind generators, and a modest battery bank equivalent to four 8-D batteries and you’ve spent 35K— almost double your basic diesel engine drive system cost.

Bottom line— this is not a drive system suitable for the A-40 budget. It fails the criteria of cost & proven development cycle reliability. However it will happily drive the boat to hull speed or motor non-stop across the Atlantic at 5 knots.

But what about the “No real advantages?” Let me list a few:

1- Large, slow turning, optimally pitched 3 blade propeller, more efficient than any feathering prop.
2- Superior low speed maneuverability due to prop size and instantaneous torque.
3- Quieter operation with diesel running due to engineered sound box around the generator.
4- The ability to enter and leave anchorages and marinas with no starting and stopping of a cold diesel motor and no noise. This isn’t just a wear and tear issue, but an esthetic one as well.
5- Far longer diesel engine life because of optimum duty cycle and engine speed.
6- The functionality of an on-board generator when needed at anchor or for powering autopilots and electronics during passages.
7- Superior light air motorsailing using just enough power to keep the sails from slating. In this mode it can be close to energy neutral with solar input.
8- Zero prop drag by using just enough solar generated power to spin the prop at water speed.
9- Effective battery charging while sailing powered up at or near hull speed using the prop.
10- Battery bank large enough to sustain several days at anchor without using the generator or running the diesel drive engine to charge batteries as so often happens.

The pleasure derived from a sailboat cannot be measured in terms of simple numerical calculations, and analysis of efficiency that fail to look at all energy inputs rather than just conversion efficiencies are inconclusive.

RDE (Richard Elder)

Hi John,
I’m fully cognizant of the desirability of keeping a forum like this civil and focused upon the technical discussions that constitute its core. And only the person who wears the editors boots has a complete perspective of what comes across his desk.

That said I’m shocked that anyone would think that pointing out the obvious constitutes a personal attack or a trip down the “angry forum road.” If we are going to be that touchy it is difficult to have a real discussion.

Has there ever been a 40′ sailboat with a huge flat deck covered by 450 sq. ft of solar panels? Or one with the interior filled with 48 batteries weighing 167# each? Is there any expectation that such a beast will ever exist? By using such bizarre aberrations as examples you or your source have, by definition, employed a straw man argument.

The intent of my comments was to move the discussion away from fantasy sailboats that look like aircraft carriers to real world experience with an actual vessel. My opinions about the advantages and disadvantages of an electric drive system are based upon on-the-water cruising experience just as are yours about voyaging to Greenland. The drive system I provided a link to has an actual price that doesn’t depend upon hope and prayer for magic batteries in the future and allows direct comparison to a conventional diesel drive system, which is exactly what we need to determine its suitability for the A-40 concept.

RDE (Richard Elder)

Hi John,
The company I linked to—Propulsion Marine— offers a number of different drive packages. The one I referred to and priced has a 10 kw continuous and 18kw peak rating on the drive motor and a 14kw diesel powered DC generator. Combined with a more efficient fixed low speed 3 blade prop one would expect it to have plenty of thrust to buck an Alaska tidal current for several hours. Given a large enough fuel tank it would drive the narrow A-40 hull at 5+ knots all the way across the Atlantic, especially with a little help from solar panels and wind generators.

re. fuel burn and efficiency—– the only reasonable standard to use is actual use cycle which includes time at anchor, short hop day sailing, and ocean passages under sail, not just the worst case of continual motoring where conversion efficiency losses become more significant.

So, recalculate your comments based upon that system rather than the 5kw one designed for marina day sailing with a Catalina 30.

Still doesn’t make it worth twice as much as a conventional diesel, at least with the size of my pocketbook!

RDE (Richard Elder)

Hi John,
I liked your examples just fine — just wanted you to agree that they were straw men! LOL

Matt Marsh

Straw men (or in this case, lead-acid men) aside, there are a few points here worth reinforcing:

1. Pb-acid batteries have an energy density far too low for battery-electric drive. They’re OK for a trolling motor but not for long distance travel- you’d end up with a boat that’s 60% battery.

2. All superior batteries are either expensive (Li-anything, NiMH), subject to corporate shenanigans (NiMH), hard to control in an emergency (Li-ion, Li-poly), or too new / rare / poorly understood to be viable yet (zinc-air, Si nanowire).

3. It is always cheaper, and usually more efficient, to have as few energy conversions as possible. Fuel -> IC engine -> gearbox -> shaft -> prop will, for correct values of ‘gearbox’ and ‘prop’, almost always beat fuel -> IC engine -> generator -> battery -> motor controller -> electric motor -> shaft -> prop.

4. It is perfectly OK to sacrifice cost and efficiency in favour of silent operation, instant low-speed thrust, the option to have no stinky exhaust on short hops, and fancy gear to play with / show off. Just don’t “greenwash” it.

RDE (Richard Elder)

Taking your comments in order:

1- I for one certainly never discussed or advocated a pure battery-electric drive for the cruising mission of the A-40. Enough with the straw men!

3- Have you read my comments about the actual long term duty cycle and use that a boat like the A-40 will experience? Or perused the more detailed analysis by James Lambden? If so, what is the point of beating to death the limited case wherein one only considers diesel electric motoring with the sails furled and then concludes that that mode defines the measure of “efficiency”? In reality that specific mode will constitute perhaps 1% of the total time usage and is unlikely to exceed half the net energy budget of the quadmodal* energy source system I described.
*Prop generator, wind generator, solar panel, DC generator

4- Since your comments are in reply to a series of my posts it would seem that they are directed to me. If that is the case, I don’t appreciate being accused of advocating fancy gear just to show off or of greenwashing (AKA covering up the truth), especially when the attack is 180 degrees divorced from reality.

Eric Klem


John already hit on this in his reply but I think one of the keys here is that a model is only as good as the assumptions that go into making it. When I did those numbers that John used, I made a couple of big assumptions. The most important one in my opinion is the use profile of the boat. I assumed that it was going to be a boat that did not have regular access to shore power and needed to motor hard for long periods of time. Changing either of these assumptions does really change what you get out of this. In the post on the Adventure 40 engine, John Rushworth and I talked about this a bit and I believe that a large source of the debate surrounded how the propulsion system will be used.

Just to put the battery thing in perspective, I thought that I would mention some real world numbers for one of the three electric cars that I have designed and built. We converted a Ford Ranger pickup truck to battery electric and made a number of small efficiency improvements as well including to aerodynamics, tires, removing the 4X4 system, etc. That truck has 24 Trojan T145 batteries in series for a 144 volt pack that weighs around 2000lbs. The curb weight on the truck is now right around 5000 lbs (before anyone notices that this is overweight, we had Ford change the GVW for us) instead of the 4000 it was with the ICE. We find that it takes around 10 kW continuous to push the truck at around 60 mph so the power needs are not that dissimilar to a 40′ cruising boat. In “normal” driving, we get around 60 miles before needing to recharge or around 1.5 hours of mixed driving. Our record was 92 miles and the batteries were truly flat at that point. The good news is that the whole thing is much more efficient now with the electric drive. We used to compete at tour de sol and they would assign a MPGe or equivalent miles per gallon based on the average carbon emissions to produce the energy in the US. When competing and driving as efficiently as possible, we would typically get anywhere from 40-70 MPGe which is definitely better than the stock <20 mpg with the 4 cylinder gas engine. Even with transmission losses and all of the energy conversions when using brown power, electrics usually come out a little ahead because the power plant efficiency is higher and the drivetrain efficiency is way higher. The other electrics gave similar results. I have also competed in Formula hybrid which is an open wheel racecar class for hybrids with two different cars and the efficiencies that we saw there were not good even when significant effort went into tuning the car for it.

I really like straight electric cars for most driving but like on a boat, there are times when it simply won't do the job in my opinion because you are range or power limited. With cars, you can often have one electric and one car with a conventional ICE assuming that you are a two car family and have no problems. In a boat, you can't do this so I would at least need an hybrid but given their lack of efficiency gain for the user profile that I assume, I would just take a straight diesel.



I guess the main point is about :
– needs (wants ?….)
– technical feasability
– and costs…..
I think cost issues is made 2 different kind of costs : cost of currently available solutions, even if completely custom, and cost of industrial-type solutions, supposing that the idea gets some traction and that a few manufacurers sell enough of the stuff to offer normal industrial-type prices.

Concerning needs : electric systems might be usefull for :
– silent operation at low speed (harbour movements….)
– capability to use other energies than diesel-genset energy (shore power, photovoltaics, windmill….)
– better efficiency with electric transmission than with mechanical transmission. I am sorry to insist on this point but it looks like the main reason Queen Elisabeth class aicraft carriers use electric transmission is that they believe they will obtain better, or much better, global efficiency than with mechanical transmission, considering their use profiles.

For blue-water sailing-cruiser with much motoring time spent sail-motoring with limited power, efficiency gain can be real or very significant depending on the electric system used. Best electric system is a good gearless synchronous PM motor + advanced electric drives + good PM AC generators. I guess that is what you will find on the Queen Elisabeth aircraft-carrier. Point is that this kind of solution is not very frequent in the market today in the 40hp range but efficiency gains vs. mechanical transmission when sail-motoring can be very large (2 to 5 times…). Because this system will adapt continuously its equivalent gear ratio and will have a good global efficiency (#90%…). Nowaday this solution is expensive because it is a one-of, or a very limited volume solution. Prices should decrease dramaticaly if or when electric or serial hybrid small trucks sell with some volume because main components are the same. This solution can also use batteries (preferably not Pb-ac..), shore power, photovoltaics….. But in that case management will be more complex and will need some customized microcontrollers. I guess this kind of solution is technically very good and is feasible today, but it is probably still too expensive and still too difficult to maintain to fulfill A40 type requirements.

I think all the other solution can be described as downgraded versions of it : supress some component or replace them by cheaper alternatives to get somewhat more limited results for somewhat more limited costs. In that logic you can :
– replace gearless synchronous PM motor + advanced electric drives + good PM AC generators by much cheaper stuff (pure DC systems…). In that case electric system global efficiency will fall from #90% to #50%.
– not use batteries or photovoltaic etc…. . In that case you fall back to a very classic efficient diesel-electric transmission with no plugin mode and no recycled energy use.
– use batteries but not generator : in that case you have the plugin-mode but limited autonomy.
– ….

As I see it, the full-spec type solution with all the whistles and bells has a bright future, because if you are not serious about electrical efficiency you get very quickly into very bad figures, and in that case appropriate use-case get somewhat limited (day-boats, harbour manoeuvers etc….). Looks like Hymar in fact doesn’t says anything else, but they say it in a very circonvoluted way, which seems to mean that global electrical efficiency can never be good, which is plain wrong.

So the idea of using lower-efficiency electric engine, drivers, generator etc… just doesn’t seem adequate in most cases, and if you have a decent diesel electric transmission, then you will want some plugin capability and some photovoltaic or propeller energy generation.
So, as I see it, this kind of solution should be a hot seller when its main component reach real volume costs, which should happen naturally with electric or serial-hybrid small trucks. Before that, DIY electric drive for sailboats should be mostly something of a very nice playground where the most gifted player can make today what the other will buy in 10 years or so….

John Rushworth

Hi Eric,

I do like the point you make of ‘user profile and that gels well with John’s and my ‘depends what you want to use it for’ when it comes to propulsion choices. I think that is in part the key to understanding where electric works and does not. I still think the genral public are in the process of educating themselves about choices other than pure diesel. I launched my boat yesterday, so now I’m looking to get some real world data. Out of interest berthing her after lift in I was pulling 29 Amps @ 11 Volts (24V system) giving 3 knots in the Marina. So quiet with its direct drive. Over the year I am going to measure my power in via Mermaid shore power cable so I’ll know my total Kw/Hrs for the whole season regardless of charging source and use. IIt was good to see Jame’s Lambden’s comments as I find his sums make sense to me. PS Please remember to differentiate between British MPGe and US for cousins across the pond 😉

Eric Klem


Thank you for the good comment. I thought that I would respond with my thoughts on the subject.

Regarding selection of drive types for people who go with all electric or hybrid electric drivetrains, I totally agree with you that synchronous AC is the way to go from a technical standpoint although it can be difficult from a practical standpoint. The torque curve of an AC motor is a much better match for the load put on it by the propeller. The trouble is if you decide to put a big battery bank in there, then charging with AC which needs extra electronics might not be the way to go and charging DC may make more sense. It is also somewhat difficult to find synchronous AC components at the size range we are talking about as induction seems to be much more common and DC is even more common when it comes to propulsion systems.

The electrical efficiency available on some of the larger vessels is very impressive but we should be a little careful in comparing the two. As you point out, size and efficiency are related for a few reasons. For one, there are some economies of scale that make it easier to design these components to be more efficient as they get larger. Another reason is that the economics make it such that it doesn’t make sense to hold tighter tolerances, use better materials, etc in the smaller motors where it does in the bigger ones. Just for example, going with the NEMA premium efficiency line of motors from WEG (not synchronous as they don’t make them that small), a 40hp motor has a maximum efficiency of 93 % which is quite good but nowhere near what is possible in the megawatt sized motors. Unfortunately, if we put two of these in a serial hybrid configuration with a high end controller with an efficiency of 95%, we end up with a total efficiency of 82% and that is using truly top of the line components at their maximum efficiency point without any batteries and ignoring coupling losses and things like that. The big ships also have another advantage in that they use many gensets to provide power so they can shut some down so that the ones running run at close to their maximum efficiency point. While this is technically feasible on a cruising sailboat, I doubt that many of us would want 2 or more gensets powering a series hybrid setup even though 1 genset would likely provide an ideal amount of power for most of the time.

The idea of using a series hybrid with no battery storage as a form of electronic transmission has been around for a while. I don’t have any data for what the efficiency of the typical transmission efficiency is for marine gearboxes but the transmissions that I have worked with have often been in the upper 90’s. The series hybrid is nice in that it decouples rpm and load which is something that can really help. As the Hymar report found, at higher loads, the slight gain in efficiency of the combustion engine is outweighed by the electrical losses and it is only when the engine load drops considerably that these two become equal. I really wish that someone would come out with a multiple speed gearbox or a cvt that would do this in a more compact, simple and efficient package.

Your comment that electrical efficiency is very important in all of this is very true. Of course, if the electrical efficiency was 100%, then there would be no efficiency penalty and we would only be debating size, complexity, reliability, cost, etc. If our real goal is to build a more efficient drivetrain whether it is a diesel or a hybrid, then looking at engine efficiency would likely provide the area for biggest gains.




I guess we adressing different questions :
1) Is there any interest or substancial future for electric or diesel-electric drive as aux. propulsion of blue-water cruising sailing-boats
2) If answer to 1 is yes, is there any interesting commercial offering today for them, or any possibility for an educated DIYer
3) Is there any interest or substancial future for electric or diesel-electric drive as aux. propulsion of other kinds of sailing-boats

For question 3 there is an agreement that :
– simple off the shelf Pb-ac batteries plus DC-motor drives with shore-power and without additional diesel engines make sense today for day-boats. Limited autonomy or efficiency is not an issue in that case and you get real advantages in quietness and possibly some cost advantage vs. diesel engines too.
– more elaborate solutions with paralled-hybrid configurations make sense today for some cruising boats because of their advantages in quietness for low-power limited-autonomy usage (typically harbor manoeuvers…). Corresponding electrical equiment doesn’t need to be very efficient in that case but you need a classic mechanical link between diesel engine and propeller with a mechanical inverter that can be driven either by electric motor or by diesel. You can buy today these kind of solutions at reputable builders (Steyr…). It looks that they are quite satifactory but a bit overpriced. I guess that those prices will get down in the near future.

For question 1). If you look at the technicalties of diesel-electric large vessels drive, like on Queen Elisabeth carriers, and at the technicalties of prototype electric cars that run in efficiency competions, they use the same kind of electric motors, electric drives and schematics. The main differences is that those electric cars use photovoltaics and batteries instead of diesel generators, but the engineers that work on those big ships can work tomorrow on those small cars and vice-versa, because technics are the same. The main difficulties for high electrical-efficiency on those cars is specific power. You can’t just downsize Queen-Elisabeth engines to install them in a car because they would be too heavy, so you need, either to accept lower electrical efficiency, or to make some R & D to obtain good or excellent efficiency with better specific power.

Sailing boats can’t use downsized Queen-Elisabeth engines or generators any more than cars for the same kind of reasons, but specific power needs for sailing boats aux. propulsion are below what you need for experimental cars, so limited R & D should allow the developpment of electric motors and generators with same, or very similar, efficiency as you get on Queen Elisabeth carriers, with weights and sizes quite reasonable for sailing boats. To pay for that R & D, you will need some entrepreneurs and also some early adopters willing to pay a premium for such products, at least for some time.

Queen-Elisabeth electric drivers can be downsised without real problems and/or loss of efficiency and I do’nt see why you could not install a small very efficient diesel-electric configuration with one 40hp motor and 2 20hp diesel-electric generators. In that case you will get the same solution than Royal Navy with : good overall efficiency at all speed, plus perfect match of equivalent-gear ratio depending the speed, improved diesel efficiency because of higher diesel average load and reduced diesel wear because you will run very often on one engine only, plus you will get diesel engine redundancy and efficient electric generation for other uses….

I guess you will find such solutions on the market within a few years. Today educated DIYer can try that, provided they accept some costs premium and a good efficiency level instead of the excellent efficiency level we should get in some future.

Of course if you install a high-efficiency Queen-Elisabeth-carriers like diesel-electric transmission in your sailing-boat, you will be tempted to add batteries + plugin power + photovoltaics etc…. It doesn’t make real difficulties to do so, but high electrical-efficiency for those equipments might be a bit complex or expensive today, so limited efficiency-batteries and so, might be a good option for somme time depending the needs. Guess the prices of those equipments will lower significantly in a near future.

Marc Dacey

Well, John, although I accept your premise that electric or diesel-electric hybrids for cruising boats are not (yet) entirely practical, you are getting plenty of well-argued pushback, and that is thought-provoking on a number of fronts.

I’ve just bolted down a largish diesel (a Beta 60) in our 16 tonne motorsailer. I have a double PTO to spin two alternators if needed. After that, however, the picture gets a touch more interesting. I have 4 x 135W solar panels, a 400W wind genny and two Honda 2000s. I estimate a 1,100 Ah battery bank is going in. We are clearly at peace with the idea of diesel as propulsion, but we never wish (outside of spinning alternators whilst unavoidably motoring) to keep our batteries charged (and our shower water hot) via diesel. Solar and wind should cover it, particularly if we limit inverted DC-AC loads through judicious use of the Honda (or Hondas) for AC power tool usage.

We’ve considered, furthermore, some of RDE’s points, particularly number 9, via a towed water generator or a shaft wheel. Ultimately, we determined that the hull needed all the help it could get just sailing, and so did our budget.

We are taking great care to install the diesel optimally and to keep it happy and ourselves happy with it, but it’s only part of the plan and contributes far less in its operation to pumping in the amps than do the “greener” alternatives. This suits us as the intersection of practical and “sailing lightly upon the waters”, even if it admittedly adds cost and complexity.

The esthetic argument carries more weight in sailing than in most pursuits, we feel, as connecting with nature is an intrinsic part of why we do this. Having been subjected to the roar of a diesel in the morning to operate an inverter to power a kettle, a loud stereo and other mod cons, we’ve decided we don’t want to be that kind of a crew on that kind of a boat…thus a bit of cost and complexity in service of esthetics as well as ecology and economy.

Marc Dacey

Thanks for the concern, John, but the decks are clearer than most on our boat. The solar panels are all on an arch over the aft helm in a sort of cambered bimini, and the deck crane and wind gen are on strutted tabs aft of the stern rail…actually aft of the deck. The nesting tender takes up about four by four feet on the foredeck hatch, and the Portabote is lashed to the rail like a surfboard. Apart from boat hooks and whatnot on the pilothouse roof rails, there’s very little else to trip on, and 30 inch high pipe rails if you do. Having both fallen (while tethered) on deck while on deliveries, my wife and I understand the safety benefit of clear side decks/jacklines.

None of this would work if it wasn’t a pilothouse cutter, the marine equivalent of a back-split ranch style…we have more “zones” than most 40 footers.


Electric or diesel electric drives for anything (car, boat, aircraft-carriers etc…) correspond to requirement analysis and production volume related costs, which means that you can get very different solutions for different requirements and, for any givent solution, very different costs for different manufacturing volumes.

I would first like to correct a few misconceptions I just read :
1) The Chevrolet Volt is a parallel hybrid and not a series hybrid (see The point is that, if you compare it with a Prius, GM has got rid of the mechanical gearbox between the gas engine and the wheel of the Prius, so that direct drive of the Volt’s wheels by its gas engine can only be done at one fixed gear ratio, which is equivalent to the highest ratio of Prius gearbox. As a consequence the Volt’s drivetrain will work as if it were a series-hybrid drivetrain if you need both lower gear ratio than maximum and electric power plus gas power, but technically speaking it has the mechanical links and the architecture of a paralell hybrid, and I guess that most electric + gas real usage will be in highest gear mode equivalent, which means classic parallel mode.
2) diesel-electric drive can be very efficient : Converteam diesel electric drive being installed on british Queen-Elisabeth class aircraft-carriers have an efficiency of about 95% on a very wide range of power, and there is no reason why the same solution could not be used on a 40hp. sailboat. Of course Queen-Elisabeth engine are a bit oversised for that and, if you ask Converteam for a 40hp high-efficiency diesel-electric transmission, cost might a bit excessive, but there is no doubt that high-efficiency diesel-electric transmissions can be manufactured in the 40hp range, point is that commercial offerings at reasonable costs might have to wait until this kind of market get some volumes.
3) Boat electric drives can fullfil very different kind of needs : capability to silently leave and enter harbour for sailing day-boats without aditional diesel engines, capability to silently leave and enter harbour for sailing cruisers with aditional diesel engines, capability to improve motoring-cruising efficiency vs. pure diesel for sailing blue-water cruisers, etc….. But the electric drive that fullfil sailing day-boat needs will be different from the one that fullfill blue-water cruisers need and probably cheaper. Point is that today commercial offerings only adress sailing day-boat (DC engines + lead batteries) and sophisticated sailing cruisers who want classic diesel + inverter and a small integrated electric engine + batteries for silently leaving & entering harbours (Steyr very expensive parallel hybrids….). It seems clear that neither of those systems is very concerned by electrical high-efficiency, so it is very clear that there is no established commercial offerings for high-electrical-efficiency sailing-boat electric-drive on the market today. I guess we don’t need a EU funded research project and a 41 pages report to find that. It doesn’t make any serious technical difficulty to develop a prototype, or a commercial offering, for such a drive. It is only an egg and hen problem.

Concerning plug-in hybrids and photovoltaic or propeller-driven electric generation. Current practice and commercial offerings has focused on DC-engine plus lead-batteries electric-drive (day-boat type…) to demonstrate these solutions, although DC-engine + lead-battery are low-efficiency solutions, completely outdated if we look for high efficiency (low engine efficiency, low battery energy density and high Peukert effect losses in batteries….). There is no doubt that energy storage and generation can be used successfuly in blue-water boat. A quite convincing prototype has already been built and tested ( Point is that this prototype is a bit above Hymar expressed requirements (“High efficiency hybrid drive train for small and
medium sized marine craft”) and that those requirement are also not covered today by established commercial offerings. It does not mean that very satisfactory prototypes could not be developped today according to those requiements.

Douglas Pohl

All very good comments. I wish WA State & US DOT Government would join this forum and pay attention to spending OUR money on a hybrid vessels.

I believe that when all the numbers are in for a ferry lifetime cost analysis proposing a $22 million upgrading (no specific cost details are listed) for upgrading to hybrid that it cannot be justified – not even by a ‘Green’ supporter… KISS says that until solar efficiencies of 70% breakthroughs actually reach industry production scale not just in the lab it best to use and keep a diesel engine.

Here in cruising “paradise” (Bocas del Toro Panama) it is very hard to locate even basic parts unless you bring your own (BYO) – anything specific to make/model requires importing at a dear cost from stocking suppliers in USA/Europe. Hybrid would be same for many years if not for the boat’s lifetime.

So when talking about a new Voyaging 40 cruising boat follow the first rule – KISS!

That’s my story and I’m sticking to it.



Hi John

That was funny. By the time you got to “Aircraft carriers” I was laughing.

Superconductivity, that’s what we’re waiting for. I hate to sound like this but is it already here and they’re sitting on the technology?

Check out Stanley Paris. I hope I haven’t already pitched him. Green circumnavigation but not electric drive.

Matt Marsh

Hi Dan,
Yes, room-temperature superconductivity is what we’re waiting for.
Current superconductors (at cryogenic temperatures) are far too expensive, but if anyone comes up with one that’s affordable and that works at ambient temperatures, it would be a major advance in electric machinery. (Think smaller and more powerful, but not significantly more efficient, motors and generators.)


From the facts presented, its a no brainer. Why anyone would desire a hybrid propulsion system would be strictly experimental and have a sizable purse to accomplish.

richard s.

even though the following question is a bit off topic, still i have been looking for an opportunity to ask you john what is your view of the old saw “gentlemen never (or at most rarely) sail to windward” ? with the mention of going to windward in this string, now seems like a reasonable opportunity to ask this of you please…specifically, do you typically try to avoid going upwind as a rule ? i define upwind as anything directly hitting any part of the mast front…personally, i do try to avoid going upwind realizing this is not always possible, which is when i am thankful for my volvo diesel…thanks

richard in tampa bay (now near tortola), s/v lakota

James Lambden

Designing the ultimate propulsion system for a boat or for any application first requires a good look at the physics of the boat and how the boat will be used. If you want to motor around at hull speed then diesel will be perfect for you. The motor will function at peak performance at 2,400 rpm and you will get where you are going in a hurry. You will hear the diesel, you will feel the vibration in the boat, you will smell the diesel fuel and on a downwind run you may even breathe the exhaust.

Going Hybrid is a very sensible approach for many reasons. But first look at the physics of the boat. For each knot you increase in boat speed, you double the power requirement. So if your Adventure 40 requires 40 h.p to run along at 6 knots (just guessing), at 5 knots it will require 20 h.p., at 4 knots it will require 10 h.p. and at 3 knots it will require 5 h.p. How often are you out there in a wind that is not quite strong enough to keep the sails full when a few quiet horsepower on the propeller would be the difference between sailing and not sailing, between luffing sails and full sails.

Then lets look at the physics of the propeller. A diesel is not capable of turning a large, high pitched propeller, so off the bat the diesel is at a major disadvantage. We regularly replace a diesel with an electric motor 1/3 of the size and this is mostly attributed to the high efficiency propellers we can use. Now lets put a solar array on board the boat and shorepower chargers and offset the diesel with other sources of energy. After all, why have the diesel running when you don’t have to? Sailing is about using the natural energies that exist in the environment – why limit it to wind power when you have solar, wind generators, regeneration, a generator and shorepower?

Let’s not forget how a boat is used 90+ percent of the time – as your home at anchorage or at the dock. The large battery banks for the propulsion system can be used for the house loads, the generator can recharge in an hour using Lithium batteries – two to ten times faster and more efficiently than the 50% efficient alternator that comes standard with a diesel using AGM batteries. A diesel engine recharging a battery pack on anchorage may only be 2% efficient – a DC diesel generator may be 35% per efficient. These differences are orders of magnitude differences in efficiency which translates into range.

When a diesel runs out of energy it is out. When a hybrid with solar runs out of diesel fuel, you can just wait for the sun to fill up the batteries. My own boat is capable of travelling at 3 knots under solar power alone – that is 50% of hull speed from free energy that a diesel powered vessel completely ignores.

The love affair that sailors have with diesel is on its way out. It is just a matter of time before people realize just how many advantages hybrid or solar electric boats have over their predecessors. 21st century technology is here now, why not embrace it?

About the only argument that favors diesel is cost. A properly designed diesel electric system will be 2 to 3 times as expensive as a standard diesel. However the cost of the boat will only be 10% more and if you wanted an inexpensive hobby, you would not have chosen sailing in the first place.

It is going to take a lot of discussion like this to bring this technology into the mainstream. Currently, electric and hybrid may represent only 1% of all the marine propulsion systems out there.

The ultimate boat includes the ultimate propulsion system, the ultimate house energy system and the best living conditions possible. And this can only be obtained from hybrid propulsion.

James Lambden

Here are some resources for you:

page 12 of this magazine features an article I am extensive quoted in and page 15 their is a picture of may solar sailboat Kapowai which has been energy independent now for over 2 years.

My R and D site:

If we have not sold you yet, the future is bound to sway you over to this new technology.

Good luck with your project and let me know if I can be of any assistance.



RDE (Richard Elder)

Thanks James,
In particular your article in “Reference Point” discusses the opinions I’ve been expressing in much greater detail and with more knowledge base behind them than I could.

C. Dan
John Rushworth


Hear, hear. You are one of the few that gets it in my view and indeed your own research and resources have been invaluable. Thanks. Since your post above I have launched my pure electric wee yacht. You are so right. Sails up and a few hundred watts and my boat is already so much better and quieter than before, not to mention faster. My approach is slightly different to yours. My project was to convert for the same or less price than a diesel re-engine and come in at the same or less weight in the right places. I have achieved that. The prop issue due to the fact I run in an aperture will have to wait till next season. Currently running a 2 blade turbine 12 x 9. My calcs show a re-pitch to maybe 11. My goals were also for max speed to be 75% of hull speed i.e 4.5 knots on calm waters and motoring to be 1/2 to 2/3rds hull speed. My battery bank is 2 x 260 AGM 8Ds at 24V, with direct drive, so I gain a little with less drive friction in the serial efficiency equation than your Browning gearbox. Yet of course you have that super efficient monster screw. What a beauty. I bet they don’t come cheap! Enjoying doing the sums and now for more tests/sailing this Summer and then see what a real prop/screw can do! To spin my prop takes 3.1Volts @ 5Amps at the motor. My Victron battery gauge show I’m only pulling 18 Watts to overcome drive friction in the whole system. Spinning it up to where I have effectively no prop has shown around 1/2 knot speed difference compared to one of those boats with a prop, if you see what I mean. I’m long keel, unlike Kapowai, so my issues are different to yours. I too now believe in the coming years the diesel is dead as an auxiliary sailing yacht drive for coastal, if not offshore with more thought. Your rule of thumb 1kW for coastal and 2kW for offshore per tonne of displacement works well. I’m using about 0.75kW/tonne as my criteria was different to yours. Silent sailors rule. I can’t even hear my drive at 3 knots. Wonderful.

Paul Newman

Nice article, some valid food for thought, slightly controversial, certainly good enough to prime the discussion pumps!

While privately researching and designing a family world cruising yacht over the past five years, the challenge and excitement of ‘free’ electrical energy powering a virtually silent drive remains. I also considered hybrid drives but my true interest lies with fully electric. Even though I have nothing practical to share at this time, I have concluded that while retrofitting existing yacht designs for long range electric cruising is not currently viable, a purpose designed yacht for long range electric cruising certainly is.

Technological advances are indeed steadily making long range electric sailing more of a consideration – again here I’m talking about a purpose designed yacht and not retrofitting. Admittedly the builder of such a yacht won’t be following the decades old tried and tested route and in that may be some different risks but also some pleasant rewards.

Some of my research and designs have suggested a fully electric world cruiser with rigid wing sails for backup / additional propulsion. By the time I’m ready to build my yacht, the electric propulsion landscape would have changed for the better, making my designs even more attainable.

If I were to build an economic yacht today to cater for the needs of paying customers who want safety in a tried and tested design, then my bias would be similar to that of the article… and there’s nothing wrong with that.

Your Attainable Adventure Cruising newsletter is one of my inbox highlights – thank you very much!

Paul Newman

Suggesting the changed electrical propulsion scene of tomorrow, IBM’s Lithium-Air battery reportedly approaches the energy density of gasoline. Couple this with high-efficiency PV cells (future efficiencies), prefferably embedded elegantly into the yacht’s hull design, and cruising or world exploring becomes much less restrictive.

C. Dan

Let’s step back for a second and remember we are having a debate about the secondary means of propulsion for the A-40. John et al have already done everyone a service by sticking to design criteria that ensure that we will be using the primary means of propulsion as much as we possibly can, thereby minimizing the amount of time we should want or need back-up propulsion. We’re all sailors, after all.

Perhaps this would be a useful exercise:
Consider the target market for the Adventure 40 – over a 5 year period, if you could separate the diesel run time into three categories, what would the proportions in each:
A. Motoring at hull speed
B. Motoring below hull speed (or motor-sailing)
C. Motoring in neutral (for power plant needs)

Now it’s time for the engineers to weigh in on the following statement: “A hybrid-electric system (from a fuel efficiency perspective) makes more sense than conventional diesel if xx% of the engine run time is spent in the latter 2 categories.”

Thoughts? My gut says 50%, but maybe I’m wrong.

Eric Klem

C. Dan,

I think that you have framed the question well and I will do my best to answer it. Unfortunately, my answer on the technical side is the type of answer that engineers hate but really, it depends.

I don’t know what the target market for the Adventure 40 will do but in terms of time, we motor at close to hull speed probably 90% of the time, motor at slower speed probably 10% of the time and never run it just to charge. I am really stubborn about not using the engine unless I really have to and probably am too extreme about it but this is how we do it.

From a technical standpoint, you need to define a specific system before you can put numbers out there. On a general level, I would assume that the system can push the boat at hull speed at WOT but just barely. In condition A, the conventional engine will be the most efficient. In a series hybrid, the engine will not be running any more efficiently and there will be electrical losses of ~20% with a well thought out system and much higher with a less well thought out system. With a parallel hybrid, the hybrid system will be doing nothing so the efficiency will be very similar but with a small amount of extra parasitic drag on the hybrid system. There is an obvious exception to this which is with a big battery bank and only a short burst at full throttle but this is not possible over a long period of time.

Scenario B is less straight forward. A series hybrid will still have electrical efficiency losses but the engine will potentially run more efficiently. I am not at home and don’t have any BSFC curves in front of me but I believe that it would take a pretty extreme case to raise the efficiency by 20%. I believe that this is reflected in the findings of the Hymar report. The parallel hybrid will simply run the engine normally at reduced load and the electrical system will do nothing. There are a couple of big exceptions to this. One is a boat this is essentially a range extended EV. In this case, most of the motoring is done on the batteries and they are recharged by shore power and the hybrid system is simply there for the occasional longer trip. Another exception is when there are really large house loads. To put it into perspective, a boat drawing 5A has a house load of 0.06kW which is puny compared to the 15+kW you may well be motoring at.

Finally, charging batteries, the winner will be the hybrid. The advantage is that they can put a larger load on the engine and do it a lot quicker so that the cumulative engine losses are much lower. The exception to this is with a small battery bank that simply cannot accept the charge that quickly or one that is close to fully charged.

I hope that this helps. I don’t feel comfortable putting a single number on this as we would need to truly define the problem that needs to be solved.



As I see it, with really well though electric motor, drive and generator, you will get a 90% + efficiency and automatic continuous adaptation of the best equivalent gear-ratio at all speeds.
So, electrical losss will be 10% minus inverter mechanical losses (3 to 5%). It makes 5 to 7%.
With classic mechanical systems, gearbox ratio and propeller size & pitch will be compromised to allow max engine power both at zero water-speed, and, at max water speed without waves or wind ( 1- capability of the propeller to let the engine go to full power at zero water speed, and 2- capability of the propeller to go to let the engine go to full power at max water-speed in good sea & wind conditions…) . This is quite contradictory, because for any given propeller size and gear ratio, “2” will ask for high pitch and “1” will ask for low pitch. To obtain something satisfactory you will need to accept a small propeller with corresponding low gear ration (high propeller rotation speed…) and compromised pitch. With diesel-electric transmission you can fully optimise propeller size diameter and “gear ratio” for the main use case (90% of time…) and still have reasonable propeller + “gear ratio” efficiency at zero water-speed. There is no doubt that diesel-electric system, including propeller, will have better global efficency. I guess the improvement might be up to 100% depending the system you started from.

Eric Klem


I think that we are not necessarily comparing the same things in our discussion. You seem to feel that 90%+ efficiency is possible on the electrical side of a series hybrid. I am unaware of any system that makes this possible at the present time but I think that it would be possible at some point. The motor that I mentioned above is a premium efficiency line and two of those alone at their maximum efficiency point are below your target efficiency and things like controllers, the extra coupling required, etc have not been factored in. Also, the number that I gave was for 100% load which is their maximum efficiency point. If you look at the 50% load point, the efficiency drops to 91.5% per motor (2 required) and it will keep dropping as the load goes down, just not as quickly as a diesel engine. With current technology, there is no doubt that 90% system efficiency is possible for some operating range on very large equipment. At present, I don’t think that you can buy what you need to get you there at a 40 hp size range and designing and building these components yourself is not an option for almost anyone. There may be some extremely specialized components out there that could get close to these numbers but I think that the cost would be extremely hard to justify. Most of the motors that I would consider for this type of application are developed for continuous duty applications where the power consumption is extremely expensive so people are willing to pay a lot for small efficiency gains so they are already pushing the efficiency pretty hard.

If we then want to compare potential technologies in the future, I would compare a CVT with the system that you describe. The CVT should be capable of getting efficiencies in the high 90’s over much of its load and speed range. Unless the series hybrid had significant other advantages (large battery bank, shore power, silent operation, etc), I would choose the CVT thanks to its higher efficiency with the added bonus of greater simplicity, smaller size, etc.

It would be really interesting to see how people weight the different factors in what determines a good drivetrain setup for a boat. We have talked a lot about efficiency but why does that actually matter? It effects cost because you usually pay much more upfront for a more efficient setup but then pay less over the lifecycle. Taking a very generic example of an engine that burns 1 gal/hr and will do 10,000 hours over its life, a 10% efficiency increase will mean 1000 gallons less fuel burned. With today’s prices in the US, that will be about $4k in savings which is significant but might be very small compared to a larger initial investment. Voyaging boats will see other advantages from more efficiency as weight and volume of tankage is a big deal so if you can get more efficiency with the same overall package size, you will get more range. If you add 400 lbs of components to get your efficiency up, you would give up 40 gallons of fuel on a weight basis (assuming you compare full tanks) so you may actually shorten your range or you may increase it if the efficiency gain is high enough. Other important factors are reliability, ease of service, parts availability, noise, etc. I suspect that we would all weigh these factors differently. If I were asked to design the drivetrain of a boat, one of the first things that I would do would be to ask the marketers to weigh the importance of those things to the potential customer as well as the perceived importance. Even though one solution might be by far the best technically, sometimes you can never convince the potential buyer of that. Not being a marketing guy, I really don’t know where voyaging sailors stand and I suspect that they are a really hard group to do market research on.



Concerning efficiency of current electric-motors + drives + generators :
Big diesel electric (or diesel-gas-turbine….) transmissions for vessels have better than 90% efficiency. The main trick for that is to limit magnetic hysteresis in iron parts by keeping magnetic fields intensity at lower than usual values. This demands big low-magnetic-intensity motors and generators. Other tricks include using gearless, instead of geared, motors, which also means that they are heavier, plus some well known (20 + years old…) tricks about motors, generators and drive design.
Technically speaking those equipments could be very easily downsised to #40hp and put on the market. Nobody does that today, because it seems most likely that there is no significant market for such low-specific-power motors and generators in that power range, even if their price per pound is reasonable….

For more than 10 years, the question of electrical efficiency for electric cars has been widely and publicly debated, with competitions of university-built high efficiency electric + battery + photo-voltaic prototype cars.
You can find some informations on the web about the motors of those cars. Their builder succeeded in obtaining much better specific power than classical (very heavy…) high-efficiency motors through clever designs and advanced materials. I undersand that Prius’ or Volt’s electric motors efficiency is better than “premium efficiency” type off-the-shelf industrial motors, but lower than those prototypes. Concerning sailing-boat aux. propulsion, you need better specific power than big vessels, but you don’t need as high specific power as cars. In fact you are in the same category than light trucks or delivery van, and fortunately, there has been some R & D investments and some products offerings for that. Plus, chances are that thoses products will improve, and also get cheaper in near future. So component cost might get very reason ables once this market has really caught up. Tho years ago, I have seen a Canadian industrialist who presented at Paris Salon Nautique, a very impressive solution based on electric-trucks motors and advanced batteries and controllers in the #200hp range. He was not yet in the 90%+ efficiency for 40hp, but it looks he was not far from that and getting closer.

I don’t think CVT have much future in boats. I guess you could more easily adapt a classical mechanical 4 gears + rear gearbox and use the top gear if motor-sailing, this might improve motoring-cruising efficiency quite a bit. I guess this has already be tried in the past without real commercial success, it can not be very clean if you try to adapt a standard car gearbox, and, a good looking prototype with specially designed and built gearbox would be expensive.

Electric, or diesel-electric drive can easily offer quietness in some situations, capability to use shore power, and, capability to use some in-board photovoltaic etc…. If you also want good or very good efficiency, things get more complex, and at least today, more expensive. In “some future” (less than 20 years….), it’s a save bet to say that very efficient diesel-electric drive with good shore-power and photovoltaic etc… capabilities will be available at reasonable costs. Concerning reliability and maintenability, those system offer real advantages vs. purely mechanical solutions, because repairs is mainly based upon component exchanges with most of the component being electronic cards or so, and the largest being the electric motor or the alternator, which are much easier, and cleaner, to replace than diesel-engines cylinder-heads for instance. Plus, you can include redundancies in the system.

I am not worried about marketing because of the good image those systems will obtain because of the successes of the Toyota Prius etc…. I am more worried about field-maintenance for the most-elaborate systems, high-efficiency component cost at current date and fiability of the most-elaborate systems. So I think that, for those systems, we are still for some time in a educated-DIYer or early-adopter market. For simpler not very efficient systems, it looks like you can already find a few serious “industrial” offerings.

C. Dan

Thanks Eric,

90/10/0 seems like the extreme end of the spectrum, but maybe that’s “normal”. I would love some others to weigh in.

My (limited) experience is more like: 50-55% motoring / 40-45% motor-sailing / 5% charging (usually for the fridge)

Dick Stevenson

Richard S.
Please do not write off going to windward. Two of our nicest offshore passages have skirted powerful highs. Each passage had about 10 days of 8-10 knot breezes where we were hard on the wind. This produced about 10 degrees of boat heel, pretty much flat calm seas and a quiet, predictable boat in sunny lovely weather. Progress was about 120 mile per day on our 40 foot hull which, while not record setting, was respectable and given the comfort level, idyllic. We continue to keep an eye out for these conditions, but nearer shorelines where we have been these last few years, they are harder to come by and of much shorter duration.
We were, on both occasions, fortunately heading generally on course to destination.
My best, Dick Stevenson, s/v Alchemy


Hi John,
it looks like all of the different meanings of “fuhgeddaboudit” are represented in these comments 😉
Very interesting post and comments, especially because of the controversy. I personally believe (hope) you are a little bit too pessimistic. I am wondering why we feel so strong about this, – maybe because sailing is a lot about independence. Being still dependant on fossil fuel is a bit unsatisfying. Electric propulsion holds the promise of independence and self-sufficiency.


I have been out cruising in the pre-WiFi world for a bit and just read through this thread. Occam would have me observe that a 360 degree of longitude vessel ought be maintainable through those same 360 degrees. Kubota and Ford (inter alia) have largely made this possible for normally aspirated diesels. Not far outside the G-8, hybrid electrics take on the aura of magic and their support requires the invocation of spells — or a heck of a big bank account and better courier service than we have encountered. It’s Pirsig’s “fitness for use” all over again.

Ask the diesel-electric submarine community how far they can go on electrics and the answer will shock you given the billions invested in just getting to that number. ~Half the crew on those subs is devoted to care and feeding of batteries.


1) nothing prevent you from using a paralell hybrid with a Kubota diesel configured in such a way that a complete failure of the electric motor, driver, propulsion-batteries etc., leaves you with a perfectly functional Kubota directly linked to a simple mechanical inverter.
Guess that in this case you might have to pay for the full price of a classic diesel system plus some additional components or features. But, if the real point were to travel as cheaply as possible whatever the noise etc., I guess most sailboat-guys would be flying not sailing.
I didn’t say that everybody needs an electric propulsion today. I only said that this kind of system is appropriate today for quite a few people, including a few blue-water guys, and will be appropriate for more tomorow.

2) My grand-grand-father was an officer on a fully fonctional and succesfully tested military diesel-electric submarine in 1902. I don’t really think that this kind of machinery did not make quite a few progress in the last 111 years.
Perhaps a few overly optimistic engineers in some distant country tried to obtain functionnalities much superiors to what he got in 1902 and were not quite succesful, but that is a very common pitfall when trying to copy foreign technologies, and I guess it dos not really relate to the given technology per itself….


I tried to follow the Hymar project writeup but I find it too complicated to follow within a reasonable period of time. It needs a summary that can be easily understood. What I will say though, based on my experience is that a 44 foot boat weighing 14000 pounds is not big enough to make efficient use of a propshaft generator. I guess to a certain extent, that would apply to some of the other ideas they tested (They did say that regeneration did not slow the boat down which I agree with). My boat just makes it at 49ft and 24000 pounds, fixed 3 blade prop, using a special 24v 70a alternator. This system draws 3amps so needs some speed management to optimise when it should be switched on or off. It will do 40a at 8kts and about 5a at 4.5kts.
Maybe this is an unfair statement given that I have not read the report, but I think more would have been achieved for the 3 million had the boat been 70 ft. ………………….(Aluminium of course!!)

John Rushworth


The HYMAR test boat, post Nigel Calder’s Malo. She’s a HB and displays the ‘iPad fancy stuff if you like’ live when sailing. I use Marine Traffic ‘My Fleet’ to know when the test boat is out as she’s got AIS and you can get AIS messages emailed. That’s the sad type I am 😉

Ed Joy

A small diesel – especially a low RPM, high torque model selected for moving a displacement hull – is already very efficient for propulsion and a well designed sailboat consumes a small amount of fuel as it is. The marginal gains in efficiency gained by by even a future revolutionary electric motor will not recover the extra cost even over the entire lifetime of the system – or its owner. For the foreseeable future we are stuck with liquid fuel since there nothing that comes close to its energy density. I calculated the energy coming out of my local fuel pump to be 18 MEGAWATTS. Our efforts for the time being should be spent on making our existing technology as efficient as possible.


1) most sailboats diesel aux propulsion systems are very ineficients at lower than 80% max. power, mainly because propellers and gearbox ratios are chosen as compromise between traction à 0 water speed (“bollard pull”…) and max speed at full power. As a consequence global efficiency of those systems at 10 to 50% of max power is not good, and life-expectancy/maintenance costs of diesel engines used mainly in those power ranges is not good either.

2) marginal gains of very mature diesel-electric systems as used today in aircraft-carriers or passenger ships is very good, and there is no reason why similar, or more elaborates (plugin, photovoltaics ….) systems applied to sailing yachts should not give similar results, plus the better quality of life those system can provide, considering that quality of life is supposed to be the “raison d’ètre” of the sailing yachts. Point is that costs or performance levels of electric aux prop systems for sailing yachts currently provided by yachting-industries are not (yet?…) very good, and that we are still today in an early-adopter market. I guess that it won’t last very long (chickens and eggs ?…), and it should not prevent educated DIYer to obtain good price/performance levels today, provided they do some homework.

John Rushworth

Ed, I have to start by saying you are wrong. You statement sounds factual and confident yet have you done your sums? As you are an experienced sailor and yacht designer I would like you to validate your assertions for the sake of clarity. For the last few hours I have been thinking about your post and this thread. What we are all talking about is energy conversion and the efficiency of that conversion. My ‘thinking’ based on my BMR (Basal Metabloic Rate) to exist is around 5 watts per hour. That assumes having to eat around 2,000 calories a day before doing work i.e to move, to travel. Apparently the brain takes around 25% of that BMR, so I guess a few hours of thought, say 2.5 Watts is a good investment! Mind you a Google search and use of my laptop to read more about you on your site consumed far more energy!

Let’s just call the motive power of a yacht, ‘the prime mover’. That can be sail (what we all want to do and free prime mover power at that) and/or an engine of whatever kind. Taking a diesel with say a peak efficiency of 35% and an average of around 20% why would you talk of marginal gains? My electric yacht which I have been doing sea trials with the last few weeks (She’s a Chuck Paine design, for whom you worked) has a prime motor mover of 90% peak efficiency and say 85% average. That is no marginal gain. Overall system efficiency through to the propeller is a serial efficiency equation. Mine has no gearbox as it does not need one as torque is produced on demand based on prevailing conditions. The speed constant is in Volts which is RPM and Torque is a current draw constant based on demand. Electric motor sail and for a set voltage/throttle setting the prop draws whatever torque/current it needs subject to the boat speed. Regarding efficiency, by the time I get to the prop my electric propulsion system has the ICE beaten hands down in overall system efficiency. Say my EM was running at 1kW @ 90%, that means the 10% in heat/friction has zoomed off into the atmosphere i.e a 100 Watt light bulb of waste. That 1 Kw can drive my Victoria 800/Frances 26 at around 3.5 Knots in calm conditions i.e 1 1/3 hp. One of the reasons I have replaced my 10hp diesel by a 3.33 hp electric motor.

The only reason we are not all electric with a sail boat is as you say the energy density in the volume and weight of 1 litre of diesel and our obsession and love of fossil fuels because of that. The power available for conversion in that litre is 11.1kWh. For that litre say at 3.5 knots using my old 10 hp diesel I could travel under motor alone about 3.5 NM. Carrying 50l of fuel, then clearly that potential range whoops my 140Kg of 2 x 8D size 260 AH @ 20 Hr rate batteries that has 6kW of stored energy.

So why have I gone electric you may ask? My design and project criteria and/or user profile of my boat is quite different to John’s ADV 40. My goal was to re-engine to electric with the equivalent power for the same or less than replacing with a new diesel and to keep the weight the same or less and in the same places. It is less out of interest and in the right places or better. I have achieved all that. I have also calculated my lifetime and running costs, not to mention simplicity, which are all less.

Range anxiety then is what all folk need to consider. My profile is to sail in F3,4, & 5 in coastal waters. Don’t mind a 6 but don’t want to be in a 7 again with a 2m beam boat. In fact why venture out at all where a breaking wave equivalent to the beam can capsize you? Of course we can’t all afford that big boat to mitigate that or even need it to have worldwide adventures. That is another thread about risk/reward analysis.

My range on a full charge down to 50% DoD is 2 to 4 hours subject to speed and current draw for pure motoring and up to 10 on electric sailing. Going to 80% is my reserve where the cycle life of the AGM batteries reduces to around 200 as compared to around 500 for a 50% discharge.

Fitting electric you basically get a feathering/folding prop for free from your old fixed one, before you realise you can now re-pitch upwards due to the instant torque nature of electric. It only takes 18 Watts for me to spin my motor i.e to overcome friction in the whole propulsion system. Try doing that with your ICE. Now if I put up the sails and blow away at say 4 Knots I can set the throttle to add say a further 180 Watts which turns my sail boat into the best sail boat of all. That is one without a propeller. That gains me about 1/2 knot boat speed. No expensive prop purchase required. If my boat were not a long keel and 2 blade propped then the boat speed gain would be say double that. Dragging a 3 blade fixed bucket behind you is a bad idea! At 4 knots my boat needs about 70 lbs of thrust to achieve that speed. Throw a bucket on a rope out the back at that speed and see what happens, as I am sure you know.

To finish off for now and as my passion from my various skills and qualifications is energy conversion and efficiency – then I leave you with this thought. James Watt was born but 10 miles from me on the Clyde and here I am settled in my place of bliss in Rothesay having served in the RN on a Rothesay Class frigate. I’ve come full circle, starting out in charge of creating steam for the prime movers and all auxiliary services, fresh water, refrigeration, diesel and steam generation etc etc.

My boat back then produced 22,000 Kw shaft power. The complement of men was around 220 on that 370 ft boat of 41 ft beam. She’d cruise at 20 knots, top out at nigh on 30 and go around 5,000 NM @ 12 knots on 400 tons of fuel oil. Funnily enough in considering the warship as a bus, it transported us all at the cost of 100 kW per man prime mover power in up to off the Beaufort scale 60 ft seas to boot, with off course the power to maime and kill too! Scary numbers however you look at it!

48 motorcycles and around 35 cars, vans and pick ups later I have finally seen sense, given up steam and ICEs! Two motor cruisers, the last of which consumed 30l/hr at 22 knots was way more than I could afford. Now you know why I want sail and simplicity and efficiency with the lowest possible cost.

Note – As this week we moved and passed world carbon emissions and targets many have agreed to, then now of all times to my mind, we all need to consider our energy conversion and use of non re-newables. In fact we need to consider what we consume full stop. What is the cheapest home and transport? Probably a small sail boat with wind as a prime mover. Cost/pleasure per mile it is tough to do it cheaper. A bicycle or walking the world is not a home yet it is very efficient in terms of energy conversion. In fact I’ll leave you with this thought. If I hook up a bicycle crank to my prop shaft I can sustain an hour or two of probably up to 1.5 knots. Personally at my age I’d rather just eat and sail as efficiently as possible with the least effort 😉

John Rushworth

Out of interest I want to throw down my electric gauntlet. I challenge any here to come for a sail with me and not go away with their interest piqued as to why on sail boats, we are not using more electric.

You may re-charge my boat however you choose. I don’t care if it is nuclear, petrol, diesel, bio-fuel, solar, wind or human powered – as long as you think about it.

I am not yet offering commercial ‘electric sailing experience’ days although SY ELEKTRA is now the UK’s very first pure electric propulsion commercial sailing yacht. She is now coded as a small commercial vessel to MCA Cat 2 (60 miles from a safe Haven) for 4 persons, having complied with MGN 280 for the standards of construction, safety and stability, for the area of operation above.

Next year subject to my health and viability after this season’s shakedown, I hope to offer commercial ‘electric sailing experience’ days around the historically famous River Clyde and West Coast of Scotland. In the meantime I welcome pleasure cruise guinea pigs!

I think James Watt from Greenock would approve and enjoy it, as was this genius still alive – in but a few weeks time he could still see steam on the Clyde.

Paddle Steamer Waverley, Steam Vic 32 Clyde Puffer plus the quiet and e-powered SY ELEKTRA plus of course some stinky diesels. I wonder which ones he would approve of?

Douglas Pohl

When you come across a real world example of a Solar Powered Boat you want to share the details – especially after weathering through all of the above intense hyperbola… so here is a real story of someone who has built it, done the Great Loop and bought lots of pizza… so this real world example speaks volumes… it’s a refreshing story I came across on – here is the text to enjoy!

Cruising America’s Great Loop in a Solar Powered (41 Foot Steel) Canal Boat.

To learn more about Bill, Cynthia and Dragonfly visit

John Rushworth


Very interesting. Thanks for the link. The AGNI is a (Cedric) Lynch motor invention. Mine is the LMC Ltd version from Trevor Lees. Trevor and Cedric worked together initially. I’m thrilled with my motor and continuing my shakedown tests. I too would like solar but of course on my small Chuck Paine designed yacht, there is little room. So, for me, my sails are the extra power of the canal boat’s backup Yanmar diesel. And sails are much more powerful than that or any solar panels I could fit. The Lynch type motor is wonderful. I run at 24V without gearing. It is quieter and more efficient in my case. Current draw at the battery at 3 knots is around 24 Amps from my 2 x 260 AH @ 20 Hr 24 Volt string. In the last days I have been programming my controller and as soon as I have an opportunity to take my boat up toward hull speed of 6 knots under sail, we shall see if I get prop re-generation. After a few weeks now on the water with pure electric drive (save a backup 400 watt/20 year old portable Honda generator) I can see why many are simply ‘not getting’ electric propulsion, especially as an auxiliary engine for a sail boat. My boat average speed with electric and sail is clearly better than it was before, for a very small current draw that will get up to 10 hours from my batteries down to 50% DoD. For 50% DoD I project it will be a 500 cycle life and it would be a 200 full cycle life if I use 80% DoD. Silent electric sailing is awesome. Enough from me, I need to go and get more real world data.


I guess this point also relates to how much modernity, and which modernity, seems appropriate for the A40 project and/or for todays reasonably priced blue-water sailing-yachts in general.

I understand that :
– the whole technical approach for the A40 might start from a 1988 (25 years ago….) McCurdy & Rhodes NA44 STC MkI 10% shorter and with larger main sail and smaller jib or jibs.
– next question is : what other points should/might be modernised/altered in 2013. I guess that recent Naval Academy & David Pedrick’s work on the NA44 STC MkII should be technicaly interesting. This work consisted mainly in designing a new hull with ratios very similar to McCurdy 1988 hull, but inverted instead of classic keel, and using slightly more composite materials than 25 years ago.
– next question, is, could a NA44 STC MkII with sluter or cutter rigging and classic interior, the 1988 way, instead of Navy specific interiors, meet the market today. That is attract enough buyers to pay for itself, plus all the fixed costs tied to a reasonably industrial manufacturing approach. At least today, answer seems to be clearly no. First because neither its builder (Pearson Composites…), nor any other established boatbuilder seem to have manifested any visible interest in starting this kind of project, although some of the studies and perhaps some tooling paid by the US Navy could probably be reused at friendly costs. Then because generaly speaking it is very difficult to sell upgraded antiques. Most customers like modern equipment, a few customers like antiques, even sometimes “remanufactured” antiques, that is new bikes, or cars, or perhaps new boats, identical to 25years+ products, and, quite a few customers also like modernised antiques, for instance technically very modern cars that evoques some antiques cars (BMW new-Mini etc….). Generally speaking, military and government agencies are very fond of “upgraded antiques”, but all the other would-be customers are just not interressed by the concept. They demand either product that convey a clear image of modernity (the majority), or assumed non-modern products that convey an image of legitimacy (the minority). Today, you can even buy products that convey both an image of modernity and an image of legitimacy (new-Mini etc…), but nobody is trying to sell to the public products that convey neither a substancial claim for modernity (too similar to 1980′ products), nor a substancial claim for legitimacy (too dissimilar from….), only governments is reputed to buy that kind of stuff.

So I guess that would-be industrialists showing some interest for the A40, or for some similar blue-water yachts, will have to chose their positionnings between “modernity” (I guess the “Boréal 44” is positioned that way), “really modernised antique” (à la BMW new-Mini…) or perhaps “remanufactured real antique” (corresponding market segment is probably smaller, but might be a good niche positionning.). As defined for the US Navy, David Pedrick’s NA44 STC MkII conveys an “upgraded antique” positionning, which is supposed to be a commercial dead-end when looking outside governments in general. So any serious would-be-industrialist looking for this kind of projects will have to decide a clear strategy to avoid that. I guess he will have different options and different strategies to reach those options. A quite decent strategy might be to make a very green 1980-looking boat, that is a boat ressembling the McCurdy’s NA44 STC MkI but using only, or mosly, limited-environmental-footprint materials, energies etc….. I guess this boat might present a good mix of modernity and legitimacy (“green” = “modern”….), respect the 200k$ limit and would use electric-hybrid aux. propulsion….


read…… seems to have gone round the bend trying to dis electric drives…. i sail and try not to motor… i need motor only for backup… about an hour of emotoring will get me out of any place i enter…. serial hybrid with diesel/dc gen, Li batteries, regen, solar and wind charging seems ideal for me… running the diesel to run the electric would be a very rare event….. low resist bearings with prop turning right at sailing speed requires little juice…. curious about prop size and configuration at this point, assuming larger diameter/pitch on a symmetrical prop is probably the way to go…. any thoughts?

peter hopper

I like this article. I’d like to have the opinion with respect to a Tesla Alike configuration, specifically with regard to Sail boats ie. Motor under electrical power, for the short distances needed to get in and out of marinas; and generate via the inverter on the same ‘drive shaft’ to ‘regen’ the batts. This seems to be a different app and hence would lead to different conclusions. O to use high energy density LiCo batts might be a bit scary – but one could use LiPo batts and a good BMS. But lets just talk about efficiency and time of use and time fraction for generation. Is this a good idea? you thoughts?



Thanks for this once again very enlightening article. What I take out of it is that combustion engines are a fundamental misconception and should – considering the advancement of battery technology – scraped. This might sound a little harsh as a starter. But look at the enormous number of shortcomings and disadvantages diesels have and that are well documented in the article. Then compare all those setbacks with E-drives that are always running under ideal rpm/torque conditions, produce no heat, do not need cooling (normally), little to no maintenance, no diesel tanks, less wight and volume, and if equipped with a decent folding prop recover much of the energy used for motoring out of the marina whilst under sail etc. etc.
Of course, motorheads will find disadvantages and arguments against like high battery weight and low capacity, high investment, ugly solar panels and limited running time especially under heavy load. Most of these arguments can be countered with modern battery technology (Li Ion), energy recovery as above, high yield solar panels and the use of a backup generator for those who need to feel and hear the stomping and coughing of last century’s technology. By the way, if you factor the cost of running a diesel engine properly into the equation, it is actually cheaper to use E-technology over time.
For a starter look at (I have nothing to do with them), they provide an excellent solution for medium sized boats as some others do.
Think of it an welcome to the future, Gerhard


Thanks John,
Obviously this is a bit of a philosophical debate. I agree, that E-drives can not replace one to one a combustion engine without adapting the usage pattern. You would not want to run for a day on battery power and expect to have energy left for instruments, lights, autopilot and the lot. But lets not forget, we are all sailors, we use the sails to advance on our route and if the wind blows less we accept that the mileage goes down.
Motoring is for safe maneuvers in and out of marinas and other situations where sailing is not the right choice for a limited time, in my case up to 5 hours at 50% motor capacity (2 x 20hp which is equivalent to 2 x 40hp diesel output) or 2 hrs at 90%). There has never been a situation where I felt that I am lacking mechanical thrust. Isn’t relying on what the nature offers in terms of wind (and some other factors) the essence of sailing?
As I said it’s philosophical, I love feeling in sync with nature and see the time pressure reduced by relying on the available wind and at the same time feel my carbon footprint and the time overhauling stroppy engines sharply reduced.
Therefore, this question should not only be looked at from a technical viewpoint.
Cheers, Gerhard

Stein Varjord

Hi Gerhard

I’m also very fascinated by the idea of having no type of combustion engine aboard. Also no generator. I think many on this site look at that option with interest, but not with complete belief, so far. I think we’d have to use a very efficient boat with a lot of space for solar panels, meaning a light and fast catamaran, which is my choice either way. One would also have to sail when there is wind, always sail, as you say.

I think that point is harder to establish for most than it should be. I think long distance sailors should learn to detach from the stresses and time limitations they are used to from the land based slave life. 🙂 In the old days, zero cruising sail boats, long or short distance, had motors. They only sailed. Several well known long distance cruisers from more recent times also sail totally without motors. They also have no electric motors and very little of modern stuff at all.

These sailors, and those of the old days, have a standard it’s not realistic to expect many would want to follow nowadays. It’s just too much hassle and too demanding on skills. Sometimes it’s even dangerous to not have a motor.

But those purist sailors prove an important point:
The amount of motoring REALLY needed is very close to zero. The amount needed aditionally to give considerable comfort gains, is also very small. I’ve tried to calculate it on long trips i’ve done myself. Then I’ve also looked at the times we were motoring, but shouldn’t have. Most times my calc ends up at a motoring time about 2% of the traveling time. Most of it is 10 minutes at each end. If I accept motoring slowly through totally windless spots, it increases to 5-10% of the time. Those figures easily fit electric motors on solar charged batteries.

To repeat my mantra: “Long distance sailors” may look more closely at that third word in their “job” description, 🙂 and stop hurrying. We cast off to leave, and we’re not sailing to arrive but to live.


Thanks Stein, that’s exactly what I am talking about. The point is that marketing tells us what we have to do and we tend to forget to question those solutions just because everybody else is doing the same. Adapting slightly our approach to motor usage when going out sailing can make diesels irrelevant, I know it because I am doing it. And hey, there is a solar power driven plane circumnavigating the globe This is innovation and application of available modern technology. Wishing you all many miles enjoyable sailing and cut the bloody engine more often, Gerhard


I have recently finished a complete refit of my 58ft sailing catamaran. The vessel had 2 x 6kva diesel A/C gensets and 2 x 75hp Yanmar diesel engines, each fitted with 150a alternators. It had no solar panels and 600ah batteries at 24v. Everything was shot after being in charter for 12 years. So I needed to replace just about everything. I did the numbers and decided to go for the ‘series hybrid’ option. This is what I did:
Replaced the 75hp Yanmar saildrives with 4 x 15kw electric saildrives from Oceanvolt with folding 3 blade propellers from Gori, saving 300kg in weight and moving the weight amisdhips instead of in the engine compartments. Replaced the 12 x AGM batteries (useable 7,200 watts) with 12 Lithium Ion batteries (useable 24,000 watts). Almost 4 x as much storage at the same weight. Replaced the 2 x 6kva A/C gensets for 2 x 14kva D/C gensets, saving 30kg. I installed 30 x 100w solar panels on the bimini for a weight cost of 72kg.
The price for this was 14% more than the replacement costs of what was shot.
As a result of the changes, I decided that a holistic approach was needed. I changed the electrical systems to match the battery capacity and installed 2 x 6kva Inverters to run the airconditioner chiller and fan coils, oven, washing machine, water maker, etc….

What have I learned:
Installation was easy and cost less than installing new diesels, even though equipment was more expensive, especially the batteries. Total cost was pretty much the same.
I can run the Air conditioners all day without the generator running (Nice and quiet).
My top speed is 0.8kts less (9.3kts) than with the diesel, but can only be sustained for 1 hour.
Cruising speed of 7kts can be achieved as long as the gensets have fuel, which now lasts 60% longer, so I can motor at 7kts 60% further than before. If I cut the speed to 6kts, I only need to run one genset and my range at that speed has doubled. At 8kts boat speed, which is easily achievable on our yacht, we regenerate 2.2kw every hour and the solar panels give us about 14kw on average in a day. At anchor, with the air conditioner on, making 200 litres per day of water and cooking with A/C power and generally treating the yacht like you would a house, we need to run one genset for 57 minutes every 3 days only. That cuts servicing costs to around 1/30th of what they were. We had to run the gensets 24hrs per day to have air conditioning all day. The batteries can be charged in less than one hour from empty (5% of capacity) to full (100% capacity). The old batteries needed 5 hours to charge from 45% to 90%. The electric motors need no maintenance at all.
Motoring at 5kts can be achieved on the batteries for up to 5 hours. The engines switch to regeneration mode as soon as the yacht is doing 7kts.

So apart from increased range, weight savings, better weight distribution, automatic regeneration, simple installation, reduced maintenance, reduced running costs, quiet motoring and similar upfront costs to diesel propulsion, there is pretty much no need to go electric. I would never install a diesel propulsion engine again, now that I know better.
If it’s done right and the correct specialised equipment used, by manufacturers that have a track record then many more people will start doing it this way. Electric propulsion has been given a bad name by installers who are not specialised in this field and use equipment that is not intended for this use. I have had nothing but fantastic performance from my electric installation. Why lug around a massive diesel engine for propulsion, on a sailing boat, when it is used less than 30% of the time?

Dan Manchester

Hi John,
I know I am well late to this topic, however it’s very interesting. I agree that current technology does not provide a viable solution for a hybrid electric drive system, however I see that we are perhaps not far away from making it viable with advancing technology.

*Battery technology is developing so quickly that it will soon be viable to store significant amounts in a reasonable space.
*Diesel generator efficiency is constantly improving.
*Electric motor efficiency is constantly improving.
*Supplementary electricity generating technology is improving constantly.

Surely one would think that any efficiency losses compared to a direct diesel drive, could soon be more than compensated for by ‘free’ energy from solar, wind, and water. And, given an adequate battery storage solution as a buffer, the system could also set to run at peak efficiency at all times – e.g. generator outputting 8kW but the electric motor only running at 5kW with the balance going to storage.

Dan Manchester

Hi John,
I would say the advances in diesel engine efficiency will likely be much greater in the generator market, which is much broader, than in the cruising sailboat market. However, I see the benefits as perhaps more intangible than just a pure efficiency discussion. Given sufficient advances in battery size/weight : storage ratio, it potentially allows a much smaller generator, backed up by improved solar systems and/or other methods. The generator could be located in a more accessible and convenient location, with better sound/heat proofing, and run when it suits the crew.
I recognise that we are a few years off the battery technology to allow it, but I think it’s conceivable that the drive motor will eventually become just another piece of electrical equipment on the boat, with the generator a part of the system that keeps it all charged and running.


Not sure if an update on this subject will help: I noted the last comment was posted in 2013.
The Lithium Iron Phosphate (LFP) tech is what I will write about because that is my experience. I will qualify my assertions by stating I am not an ‘expert’, engineer, electrician. I am a guy who has lived aboard my cruising sailboat for the past 30 years: I know from my own limited experience what seems to work and what does not on my boat.
OK…. it really is a ‘no brainer’ with the LFP tech: it is a huge improvement. In reading article there seems to be this scary concern over safety…. No battery on a boat is without it’s safety concerns. It is a matter of what we are habituated to and are willing to accept. Rod Collins of HowToMarine has done a real good job explaining safety concerns with the LFP tech… they have shot holes in the cells, lit them on fire, overcharged them…etc…… NO catastrophe…..
The LFP is safe especially when combined with a BMS (battery management system). I my opinion this is an absolute requirement.
The LFP batteries are near zero impedance devises meaning they will accept all the amps that can be thrown at them when charging and they are nearly 100% efficient (CEF): no charging for hours and hours to replace used energy.
I replaced my 660ah Lifeline AGM house bank with a 400ah Winston LFP pack almost 3 years ago. I investigated this upgrade for almost 4 years before taking the leap. It is a total boat charging system upgrade…not just the batteries.
The Lifeline batts weighed over 500lbs and the Winston pack 113lbs. The usable capacity of the Lifeline bank… about 165ah. With the Winston pack I get to use 300-350ah…. more than double….
The Winston pack recharges faster meaning I use less fuel/solar/wind/hydro….
The cycle life!!!! The Lifeline batts never gave me more than 350-450 cycles…. at about cycle 150 I started noticed an ever decreasing performance. The Winston pack I have is now at 220 cycles with no loss of capacity. I load tested the pack at commissioning and annually I repeat the load test. The starting capacity of my pack was over the manufacturers spec: I got 445 ah out of a rated 400ah pack. At my last load test (2 years after commission) I got 438 ah delivered.
The LFP batteries are rated at 2000-8000 cycles depending how hard they used. They are ‘industrial’ batteries: they are made to be used hard. The loads/charges that most cruisers will place on these batteries does not qualify as ‘hard’: most cruisers are using/charging there batteries under what is called ‘fractional C’ conditions. What this means is for a 400ah pack like mine, 1C is equal to 400 amps. One would need to load or charge at 400 amps to be using there batts at a 1C level. Cruisers do not do that. We use are batteries at a ‘fraction’ of 1 C.
Anyway, with fractional C usage, this battery technology will go for years without any performance issues. They could very well be the last batteries you will buy. For me, shelling out $3500.00 every 3-4 years for new AGM’s, this was a ‘no brainer’.
We never really worry about our battery SOC anymore (state of charge) because we have so much usable capacity and the batteries are so easily recharged with renewables.
I will emphasise that this upgrade is NOT just batteries …. one needs to beef up their entire charging system.
Never ever over charge or over draw amps from the pack because that will kill them…. a good BMS is designed to protect the system… it is IMHO absolutely necessary.


Thanks John,
I read some more from some of the other people who have contributed.
The BMS protects your investment…. on a good unit you set the values for max charge/ max discharge. The BMS controls large NO (normally open) relays called ‘contactors’ that remain closed when everything is good but will open if the BMS senses a problems.
The BMS can be bypassed in emergencies. In this case you must watch the voltage on a seperate battery monitor or multimeter. The BMS I have is a plug a play affair so if for some bizarre reason it failed, unplug it, plug in your spare and then upload to it the parameters from the failed unit.
Cost >>> there was some misconception that the LFP tech is super expensive:
If one buys a packaged system and then pays someone else to install… then yes… super expensive.
One should know that all the LFP cells come from China. Worldwide, these cells all come from the one source, then Victron, Mastervolt, Genasun…. etc. they put their branding and fascia onto them and mark the price way up. The only people I am aware of gearing up to manufacture Lithium tech other than the Chinese, is Elon Musk.
We bought the cells directly from the Chinese vendor EVLithium in 2015. Imported them to New Zealand. Had my metal guy build our compression case. Bought an Orion BMS and paid an engineer to design the the wiring system.
All up (2015 prices): $2500 including air freight shipping for the four 400ah LFP cells, $2036.00 for the BMS, mini relays, contactors, wiring…etc.
Almost $5000.00 USD for a system I will not have to spend anymore money on.
Compare this to $3500.00 New Zealand $$ (or about $2400.00 USD) every 3-4 years for the Lifeline AGM’s
Compare this to the reduced fuel costs associated with keeping the LFP charged vs Lead Acid
Compare this to the reliability of using a battery that is not constantly losing capacity as it ages.
Compare this to the environmental impact of running an engine or genset to keep lead acid charged vs LFP and the burden on the environment of constantly (relatively speaking) replacing lead acid with new.
Regarding comments made about complexity and time involved : I agree completely with the comment about NOT just paying someone to put a packaged system in…. Cruisers need to do their own homework on all their systems and install their systems them selves….IMHO….. Yes! this takes time and energy. That is all part of the lifestyle….
The only way we have been able to sustain the lifestyle for as long as we have (29 years) onboard a 40 foot sailboat is by doing all the jobs ourselves. It is not that hard and very gratifying. There are a lot of people who do not want to do this and that is OK if that is what works for them and their wallets.
For my part I really enjoy the lifestyle and find that the lifestyle affords me the time to research, implement and then maintain all the various systems.
My advise to those interested in the LFP tech: study up and give it a try.


Thanks for that John…. I understand the viewpoint you have expressed and the motivation for it.
All the best,