Viability of electric only propulsion in 2018 - is there a good option after all?

[Paul Elliott]

Originally Posted by Augi

The extra investment for the electric motor probably does not make economic sense but it is partially offset by using less diesel, and less wear on your diesel engine.

How do you use less diesel fuel? You are connecting a diesel engine to a generator to a battery to an inverter/controller to a motor to a propeller. You will use more fuel to spin your prop with this system than you would if you had just connected the engine to the transmission and prop. Any efficiency increase from optimizing the genset RPM will in no way compensate for the other losses.

[john61ct]

Yes, just like running a mains charger of your alternator through an inverter.

Much bigger losses at each stage than you would imagine from reading spec sheets.

[Dockhead]

Originally Posted by Jon Hacking

Excuse me?!? One of the big advantages of electric propulsion is that it can recharge the batteries while sailing . .

This sounds good in theory but it doesn't work so well in practice. So you definitely can't call that "one of the big advantages" yet.

One problem is that there isn't excess power from sails as often as you might think in realistic everyday use.

And the another problem is that it is quite difficult to harvest that power in the quantities needed for propulsion, even if the excess power exists. It is an entirely different ball game to try to get some kilowatts of power from a hydro, than to get a couple hundred watts to power the race computer on an Open 65.

The good news is that this technology might improve. But whether it will ever be good enough to be a "big advantage of electric propulsion" is still an open question.

So John61 was correct to point this out. Cars waste a lot of energy accelerating and then dumping that energy through the brakes. Electric cars can recuperate much of that energy -- a big advantage. This whole thing doesn't exist for electric propulsion on boats.

I'm sure electric propulsion has a great future on water as it more obviously does on land, but I think it's healthy to keep a dose of realism in the discussion, when enthusiasts are inclined sometimes to forget the basic laws of physics, claiming, for example, that greater torque means you can use a smaller motor, or that an electric horsepower is any different from a diesel one. At this stage of the game, electric propulsion doesn't seem to offer any advantages for the typical cruiser who needs mechanical propulsion a lot and over a long range. It may already be feasible for some specialized uses, like day sailers or small cruisers which don't use mechanical propulsion much except getting in and out of the harbor.

But in any case all hail to the dreamers and early adopters! You make the world go round, and future generations will owe you a lot.

[Augi]

Originally Posted by Paul Elliott

How do you use less diesel fuel? You are connecting a diesel engine to a generator to a battery to an inverter/controller to a motor to a propeller. You will use more fuel to spin your prop with this system than you would if you had just connected the engine to the transmission and prop. Any efficiency increase from optimizing the genset RPM will in no way compensate for the other losses.

Yes. I understand. There is no free lunch, plus you have losses for each extra step.

So if you are already going with a direct drive (not sail drive), and the advantages of electric propulsion(quieter, no fumes, maybe better maneuverability at slow speeds albeit for a limited distance per charge), are worth the extra expense and complexity of a parallel hybrid electric / diesel with the electric motor and diesel engine connected to the direct drive shaft, a parallel hybrid as described above makes sense.

Since it is not being widely done, for most the parallel hybrid solution is obviously not worth it.

The truth is a diesel that is well insulated is not very loud. You can get parts for an entire diesel system all over the world. There are people all over the world that know how to repair a diesel and the related.

[john61ct]

And usually the diesel would actually be running longer, you just get a little timeshifting by using that huge battery bank in between.

[a64pilot]

Think money and weight, your Boat is now slower, cause it has a HUGE battery bank, or to save weight you throw huge plies of $$$ into it.
So now that it’s heavier, it’s slower, especially under sail so forget regeneration, cause that slows you way more, and you burn more fuel pushing more wetted area and a heavier boat.
So you think your going to save Diesel, but you end up losing a lot of storage space, and making the boat a pig to sail and you need a larger engine and of course a larger fuel tank, again driving up costs, reducing storage, slowing the boat even more and burning more fuel. But you can sneak out of the marina and not wake anyone up.

Electric propulsion does have a place in my opinion, and that is for the majority of sail boats, the majority don’t ever go very far from their home marina.
Electric propulsion could take less room and even be lighter weight and less complex than many Diesel installations.
Think take a smallish, very light weight, high performance Boat and stick a big trolling motor in its rudder with a folding prop. Enough power to get you into and out of the marina and not a whole lot more, but you could lose the Diesel, and it’s weight and gain a lot of storage.
Of course it’s not motoring down the ICW though.

[GrowleyMonster]

I have all electric propulsion. I designed the plant, sourced the components, made it all play nicely together, and I am happy with it for my needs and will be even happier when I have my 2kw of solar canopy up and running. So I think I am qualified to pitch in here.


No, for most applications, a straight serial diesel/electric hybrid plant is NOT more efficient in the long run. As others have said, there is too many stages of energy conversion, and no conversion even remotely approaches 100% efficiency. The only thing you would gain is greater maneuverability (no minimum idle speed, instant on and reverse) and the ability to motor on battery only for short duration quiet runs. And this could better be done with a parallel hybrid setup, anyway. The only way to make a hybrid in sustained, multiday use, more apparently efficient is to get free electricity from a very large solar panel array. Forget about wind. To get a reliable 1kw in most places, you need a turbine with an approximately a 10' diameter swept area. That's just 1kw. At 48v that is just 20 amps. On a sailboat, your solar capacity is severely compromised by shading. Regen robs you of considerable speed under sail, typically a half knot, for a small amount of charge, which is insignificant, usually, at under 10kt anyway.


A motor cruiser with hybrid propulsion and plenty of solar is viable. You won't save much money over the cost of a diesel and fuel, though. You can have range, or you can have reasonable speed, or you can have a manageable battery. You can only have one, your choice. Usually we figure on going slow, having a big bank, and going far. For the size boat you are talking about, the solar needed is just mind boggling, as is the bank required. LiFeP04? Better have deep pockets. Tesla car pack, or Power Wall? I won't touch that in a boat. Nowhere to run to. TelCo cells would be my choice. And high voltage. Maybe a backup bank of NiFe Edison cells. (they last essentially forever)


Best application for electric is a pure electric setup, charging from shore power, for a day sailer or weekender. In fact, for this application, an infernal combustion engine is just plain stoopid. This is where electric drive shines, not cruising. For cruising you have to accept and allow for a lot of drawbacks versus straight diesel drive. Of course with parallel hybrid, you can simply ignore the electric drive motor anyway, and operate in straight diesel mode on a passage. The electric motor simply serves as a big alternator keeping a huge bank charged and keeping your air conditioner and electric range working. And of course maneuvering at the dock.

[BigBeakie]

All of the commenters that are claiming regeneration from A serial electric system is not adequate battery charging need to sit down , watch the Oceanvolt presentation on the Servoprop regeneration, and then go make themselves a cup of tea and do some THINKING.

Look at the numbers, do your sums, combine them with the numbers from a multi kW solar array. I have posted those numbers, several times, but some seem to have selective memories on this point.

If you have a cat that can sail at 8 kts, you could be generating about 3kW of charging. Plenty of cats can cruise more towards 10 kts & then we're talking about double that again. So now it's like you are cruising with a 6kW genset running full time! And if you're lucky enough to be sailing in sunny conditions and you have a 2 kW solar array also contributing, isn't this good enough for you, or what? Are you really going to use more power than that? No? Well, good, then store it for when you need it.

And if your at anchor for several days in really cloudy weather and your batteries are getting down, go sailing for a few hours to recharge! You do own a SAIL boat, don't you?

And it's really calm AND cloudy, and you need recharging? Well, then it's time to burn some dino juice from your DC genset, as a last resort. But how often do you think that scenario is going to be? Do your sums.

No, batteries cannot carry as much stored energy as diesel, yes, we do get that, so enough already with the mantra that 400 liters of diesel can go farther than batteries. Yep, OK, got it. OK?

But stop pretending there isn't any credible alternative, because there is. And Yes, we do get that it is not for everyone, and that diesel is better for pushing boats that have huge hull resistance, or that need to motor into 50 knot head seas for days on end. But again, really, when was the last time any of you had to motor for more than an hour into seas you couldn't sail into?






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[CaptainIglo]

Thanks GrowleyMonster for what seems to me the best reply yet.

How about this crazy idea:

Since most people think pure electric propulsion will never be a competitive option mainly because it would be impossible to produce enough power aboard, I have also been thinking about how to increase solar surface on a sail boat: I’ve had this moonshot like idea of a floating solar array that can be towed. When it’s folded away it can be stored below a dinghy, when it’s deployed it can be kept afloat by inflated airbags or air mattress mounted on the left and right side of each panel.

You would want to use flexible solar panels and find a way to wrap them in a salt water resistant material (one that should not reduce solar efficiency) you could tow an array without producing too much drag, no? Folded away that whole thing wouldnt be more than 20 inch / 40cm thick. The airbags could be inflated with a compressor.

A 200W panel is about 1445x785mm / 56,8 "x30,9"
So a 10 panel / 2000w array would tail the boat by about 8 meters / 26 feet

A 20 panel / 4000w Array would be 16 meters. Of course the deployment of these would be limited to when at anchor or in calm seas (which, going back to electric propulsion again, could be a use case to produce enough power to drive the electric engines)

I’d like to ask if anyone can point out reasons why this wouldn’t work. I’m looking for reasons that are insurmountable or if you think that there are surmountable issues please pitch in with ideas how to fix them.

Is this a totally insane idea or is there a chance that this could be made to work?

And as a final point:
Some posters compared the motivations for going all electric to something like a naive, do gooder plan to save the planet which they then pointed out is of course total nonsense because the production of electricity / batteries / panels causes pollution. Without getting into the merits of this argument (which I do think is flawed) I’d just like to reply that there are plenty of reasons to do this that have nothing to do with altruism or saving the planet. Actually to me that wouldn’t even be on the top of my list. How about no exhaust, no noise no vibration for starter?

As a64sailor pointed out, please be gentle, keep it civil and let’s separate opinion from fact. I’m just a newb with too many ideas who wants to sail the world off grid.

[CaptainIglo]

Sorry a64pilot not a64sailor :-)

[a64pilot]

Originally Posted by CaptainIglo

Sorry a64pilot not a64sailor :-)

That’s fine, I don’t fly anymore so I guess your correct.

As far as regeneration, you can’t say a Cat will cruise at 8 kts and then say well 8 kts produces X amount of power, cause drop that bugger into regen and you speed isn’t anywhere near 8 kts anymore, and I know of no cruising Cat that makes 20 kts, maybe some can, but it’s likely not very often.

You have to think that just a non folding prop will slow you by a knot, start drawing power from it and of course your speed drops directly proportional to power drawn from the system, so to work, you have to have excess power available, and that is rare.
We reef not so much to slow down, we reef because the boat is overpowered and uncomfortable or unsafe, to maintain regular cruise speed we would have to be overpowered if we are drawing 6 KW of power from the system, way overpowered.
You might can make that work with a superlight very fast Boat, but that isn’t a cruising Boat. Some may be very disciplined and do without luxuries and keep the weight and windage down, but the majority of us don’t.

If it’s so great, and viable, how come you aren’t doing what you propose, how come nobody really is? Don’t point to a concept Boat to show it can be done, cause if you believe those, then we all got flying cars right after WWII.

A few have gone to electric propulsion and if you ask them they will explain just how limited it is.

I’d tell you that it’s likely that you will go further and faster if you take 10% of that electric drive conversion money and put into making you Boat a better sailor.

[GrowleyMonster]

Originally Posted by BigBeakie

All of the commenters that are claiming regeneration from A serial electric system is not adequate battery charging need to sit down , watch the Oceanvolt presentation on the Servoprop regeneration, and then go make themselves a cup of tea and do some THINKING.

Look at the numbers, do your sums, combine them with the numbers from a multi kW solar array. I have posted those numbers, several times, but some seem to have selective memories on this point.

If you have a cat that can sail at 8 kts, you could be generating about 3kW of charging. Plenty of cats can cruise more towards 10 kts & then we're talking about double that again. So now it's like you are cruising with a 6kW genset running full time! And if you're lucky enough to be sailing in sunny conditions and you have a 2 kW solar array also contributing, isn't this good enough for you, or what? Are you really going to use more power than that? No? Well, good, then store it for when you need it.

And if your at anchor for several days in really cloudy weather and your batteries are getting down, go sailing for a few hours to recharge! You do own a SAIL boat, don't you?

And it's really calm AND cloudy, and you need recharging? Well, then it's time to burn some dino juice from your DC genset, as a last resort. But how often do you think that scenario is going to be? Do your sums.

No, batteries cannot carry as much stored energy as diesel, yes, we do get that, so enough already with the mantra that 400 liters of diesel can go farther than batteries. Yep, OK, got it. OK?

But stop pretending there isn't any credible alternative, because there is. And Yes, we do get that it is not for everyone, and that diesel is better for pushing boats that have huge hull resistance, or that need to motor into 50 knot head seas for days on end. But again, really, when was the last time any of you had to motor for more than an hour into seas you couldn't sail into?






Sent from my iPad using Cruisers Sailing Forum

Have you actually owned or operated the above described system, and observed the above described regen yields? Sailing at 4.5kt with a 5kw motor I managed to get 140 watts with a fixed prop. This for a nearly half knot loss of speed as verified by setting the throttle to zero amps in or out. Smaller boat, lower speed, smaller motor, but scaling it up falls far short of those figures. Just sayin. You might also ask other guys with electric auxillaries. Regen is useful but is not all that. At 10kt it is a significant means of charging. How often do most of us sail at 10kt for days on end?


UNSHADED solar panels are a much more important and reliable source of charge than either regen or wind turbine.

[GrowleyMonster]

Originally Posted by CaptainIglo

Thanks GrowleyMonster for what seems to me the best reply yet.

How about this crazy idea:

Since most people think pure electric propulsion will never be a competitive option mainly because it would be impossible to produce enough power aboard, I have also been thinking about how to increase solar surface on a sail boat: I’ve had this moonshot like idea of a floating solar array that can be towed. When it’s folded away it can be stored below a dinghy, when it’s deployed it can be kept afloat by inflated airbags or air mattress mounted on the left and right side of each panel.

You would want to use flexible solar panels and find a way to wrap them in a salt water resistant material (one that should not reduce solar efficiency) you could tow an array without producing too much drag, no? Folded away that whole thing wouldnt be more than 20 inch / 40cm thick. The airbags could be inflated with a compressor.

A 200W panel is about 1445x785mm / 56,8 "x30,9"
So a 10 panel / 2000w array would tail the boat by about 8 meters / 26 feet

A 20 panel / 4000w Array would be 16 meters. Of course the deployment of these would be limited to when at anchor or in calm seas (which, going back to electric propulsion again, could be a use case to produce enough power to drive the electric engines)

I’d like to ask if anyone can point out reasons why this wouldn’t work. I’m looking for reasons that are insurmountable or if you think that there are surmountable issues please pitch in with ideas how to fix them.

Is this a totally insane idea or is there a chance that this could be made to work?

And as a final point:
Some posters compared the motivations for going all electric to something like a naive, do gooder plan to save the planet which they then pointed out is of course total nonsense because the production of electricity / batteries / panels causes pollution. Without getting into the merits of this argument (which I do think is flawed) I’d just like to reply that there are plenty of reasons to do this that have nothing to do with altruism or saving the planet. Actually to me that wouldn’t even be on the top of my list. How about no exhaust, no noise no vibration for starter?

As a64sailor pointed out, please be gentle, keep it civil and let’s separate opinion from fact. I’m just a newb with too many ideas who wants to sail the world off grid.

Your floating solar array presents a lot of technical and practical challenges. That is a LOT of drag, especially for a smaller boat. Insulation and isolation would be tricky. I considered fold-out solar wings, actually. And a folding solar "tail" hanging out over the stern. This all in addition to a full hard canopy over the entire boat covered with solar panels. BTW I don't have a mast or sails to shade the panels. But I believe wings and tail panels might be more practical than floating panels. Nevertheless it is worth trying. Your idea, your $, LOL! You might be better off with a floating catamaran thingie (well, actually one would EXPECT a catamaran to float, so please, no cat/mono war or jokes LOL) covered with solar panels. It could be towed far enough aft to (1) not collide with the mother ship, and (2) not be shaded by mast, boom, or sails. It would create less drag in the water, I think. With some sort of transponder on it Sort of like a SART, you could cut it loose and retrieve it later.

[BigBeakie]

Originally Posted by a64pilot

That’s fine, I don’t fly anymore so I guess your correct.

As far as regeneration, you can’t say a Cat will cruise at 8 kts and then say well 8 kts produces X amount of power, cause drop that bugger into regen and you speed isn’t anywhere near 8 kts anymore, and I know of no cruising Cat that makes 20 kts, maybe some can, but it’s likely not very often.
Oh really? What would the speed be then, in your estimation? Because I have been on a boat that turned regen on and off, repeatedly, and watched the result. That boat was a mono, a Freedom 33, sailing at just over 5 knots in a moderate breeze. It certainly was NOT over powered by any means. Now, what is your estimate of how much the boat slowed down when switched into OV regen mode?

You have to think that just a non folding prop will slow you by a knot, start drawing power from it and of course your speed drops directly proportional to power drawn from the system, so to work, you have to have excess power available, and that is rare.Why do you conflate things? We are not talking about a non folding prop, we are talking about a variable pitch Servoprop. You did go look at the OV video on regen, didn't you?
We reef not so much to slow down, we reef because the boat is overpowered and uncomfortable or unsafe, to maintain regular cruise speed we would have to be overpowered if we are drawing 6 KW of power from the system, way overpowered.
You might can make that work with a superlight very fast Boat, but that isn’t a cruising Boat.How about a Slyder 47, is THAT a cruising boat? Have you seen the Slyder regen video? Some may be very disciplined and do without luxuries and keep the weight and windage down, but the majority of us don’t.

If it’s so great, and viable, how come you aren’t doing what you propose, how come nobody really is? Ahhh, actually I am. After speaking to about 10 OV users about all aspects of their experience, including regen. Were any of them unhappy about their boat slowing down too much under regen? No, they were not. The most common feedback was, "We hardly notice it, if at all." Isn't it strange that none of them noticed or mentioned the huge drag and slowing down that you state with such certainty as fact? Either they are all lying ( for what purpose?) or they are all deluded ( probability highly unlikely), or shock-horror, you are wrong?Don’t point to a concept Boat to show it can be done, cause if you believe those, then we all got flying cars right after WWII.Concept boat? A Schionning cat is now a concept boat?Is that the best you can come up with as a refutation? How about you show us some math and evidence to support your case? Like the hull resistance figures, and the drag values under regen, and the video of the boat speed changing? Got any of that?

A few have gone to electric propulsion and if you ask them they will explain just how limited it is. That's odd. I'd like to hear those comments, because not one skipper I've spoken to has mentioned limitations. What limitations did they mention to you? Several commented to me that bigger sized diesels ( HP diesel compared to HP OV) go marginally faster at top speed because of higher rpm, and that is in accordance with the figures I've given previously. But several also said the electric has more propulsion against wind.

I’d tell you that it’s likely that you will go further and faster if you take 10% of that electric drive conversion money and put into making you Boat a better sailor. You won't get any argument from me that money spent in improving sailing performance is money poorly spent. But with respect, your comments about electric regen are ill informed, at best.

As I have committed to previously, when we are in sea trails with our OV system, I will film regen in real time, without any pauses so you know there is not any tricky editing taking place, (because I just KNOW that will be your cop out) showing boatspeed without regen, and then switch it on. I'll do that in as steady a wind situation as I can, and I'll switch it on and off several times.

I think that will deal with this particular issue.

[john61ct]

Still not a significant source of power compared to what's required for propulsion in regular cruising circumstances.