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Old 13-12-2018, 07:28   #1621
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
Direct Drive requires a transmission, EP does not. 3-15% losses according to Gerr.
A saildrive consists of 2 sets of bevel gears, each with a 1%-2% loss, total 4%. It appears the OV saildrive has only 1 bevel gear set as the EP has a vertical shaft, hence it would be max 2% loss assuming they use a common bevel gear set.

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Generator power matched to cruise load on a DC bus.
Since a large percentage of the time we are cruising (as stated by both DD (direct drive) proponents and EP alike), match the generator(s) to the load at cruise. Why? Cycle it on when cruising and off when not, and you have zero battery loss. Related: Some LiFePO4 folks are claiming 98% efficiency on battery charging, but I haven't investigated those claims. If claims are real, you don't have to use this optimization, but I'd prefer to keep it because it's free, it only requires logic to implement, and it still would save 2% and battery life. Source: https://forums.energymatters.com.au/...topic6033.html

Ability to downsize the overall power requirement because we are not required to oversize. I have mixed feelings about this. DD folks point to it as a weakness because EP folks are choosing to target cruise instead of cruise + reserve. They also cry "not apples to apples", but that is silly. Ability to size correctly is a benefit that can be counted if the sizing is correct. But I have yet to find anyone who can tell me exactly how much reserve is required. To me (and maybe most EP folks) reserve is wasteful and hard to justify because you can't quantify it. How do I know if 10 or 20 or 50% more power is enough to save my bacon? How do I know that I can't save myself with my existing max cruise power? What do sailboats with tiny engines do for reserve? I would love some math on reserve power, I asked a while ago and no one answered. I will keep this in my calculations, but others don't have to (including DD folks who are used to having it and won't want to give it up regardless of whether it can be quantified, they feel good about it and that's worth something to them). It's important to note that this is not a large savings because the power requirement is still the same at cruise, so we are unlikely to save a large amount just due to engine sizing. Capital cost mostly, but we lose that in our generator because it's duty rating has to be higher (therefore bigger in any case) It might be worthy of calculating if it's 1 or 2%. It's not the largest savings by far however, therefore I list it last.


Not a factor, but a reminder that the costs of these new systems are still high, I don't think anyone is saving any money over the life of the system unless they have a design that incorporates a LOT of solar, wind, or sail regen and USE it. Today's buyers might get some efficiency, and are definitely buying a tool that allows them to be more green if they collect the "free" fusion energy all around us.

WRT to your query about reserve power. You need to observe your own boats performance in all kinds of sea/weather conditions. Then make up your own mind, there is no single right answer, only wrong answers for your threshold of pain.

All I can offer is at my 'normal' cruise RPM, according to the charts, my engines CAN produce 10KW each at the prop (20KW total). I can tell you that a headwind over ~10kts will start dropping speed and a 20kt head wind will drop speed to ~6kts. Add any significant waves (1+M), and I'm down to 5.5kts. Trying to extrapolate from this, I'm thinking normal cruise is probably ~15-16KW, headwind up to 10kts the governors cover by increasing power to 20KW, and over 10kts of headwind I need more RPM/power to maintain speed. Displacement hulls are pretty slippery, so it's really hard to gauge how much actual power is used except when the wind/wave are on the nose, I can't maintain speed with 20KW. Extreme rough conditions I have run at 15KW each (30KW total), but you get into a situation where the ride gets rough and slowing down seems like a good thing to do. But, there are conditions, like clawing off a lee shore, the ride doesn't matter. I have run at WOT for a short time to get out of a situation, but don't remember if I could even reach max RPM with current props, I doubt it.

If I were to replace DD with hybrid EP today, with what I know at this time, I would want the ability to have 30KW (at the props) for 4-6 hours and 20KW until the diesel tank was empty.

Yep, engines on sailboats are 'auxiliary' and I realize some will tell me to raise a sail, and that's always an option......until it isn't.....(crew member down, hurt, sick, conditions, etc.)
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Old 13-12-2018, 07:56   #1622
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Re: Oceanvolt Hybrid Motor

OldMan, is it ok if I ask you for your engine model numbers and boat type? It'd be nice to get real specifications to talk about for reserve. I don't doubt that they could be, but real engine data helps us understand what is actually happening and what I want versus what I get is not always the same. I want to be on solid ground in our discussion.
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Old 13-12-2018, 08:03   #1623
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Re: Oceanvolt Hybrid Motor

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OldMan, is it ok if I ask you for your engine model numbers and boat type? It'd be nice to get real specifications to talk about for reserve. I don't doubt that they could be, but real engine data helps us understand what is actually happening and what I want versus what I get is not always the same. I want to be on solid ground in our discussion.

Post #1596


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Old 13-12-2018, 08:16   #1624
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
This is because the engine is coupled to a prop, you are unable to use the engine at it's optimum SFC. Where you are using it, it has the same 30% worse (that particular engine) SFC. It can never reach the low RPM high throttle low SFC regime for best fuel economy because you can't load it at low RPM's like you can with the engine in the generator. If you were to design it to be loaded it at low RPM's, you'd never reach high RPM's and you wouldn't be able to maneuver. Think about it.

There are three flaws with this:


1. Who said anyone is limited to a fixed pitch prop? Lots of us, including me, have variable pitch props. You don't need to spend $30 000 on a hybrid system to use your diesel engine in its ideal regime, or close to it.


2. Who said your hybrid system will be capable of keeping the engine in its ideal regime? A fixed speed AC generator will be worse at that than even a fixed pitch prop and mechanical drive -- because you can't even vary RPM with varying loads. It's true with series hybrid you can supplement generator power with battery power for short term high power requirements, and that is a genuinely valuable feature for sure, but the benefit of this is mainly in being able to reduce the size of the main engine, making it cheaper and lighter. You won't get a dramatic improvement in fuel consumption because you STILL have to modulate power with varying power requirements, so you will STILL be using the diesel at different loads, not all of them right in the sweet spot. Especially if it's a fixed RPM AC generator. But even a variable speed DC generator, which you are undersizing compared to the engine you would be using in a mechanical drive system, will be operating a lot over 80% output where fuel consumption is worse. So it is not only underloading diesel engines which leads to worse efficiency.



3. You are greatly exaggerating the fuel consumption hit even of a fixed pitch prop. Here is a typical small diesel fuel map:


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And here is a typical dumb fixed pitch prop curve for the same engine, overload on the fuel map:


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You will see that at no time at typical operating speeds is the engine operating at as much as 20% less than ideal regime. A variable pitch prop easily pushes the curve right up into the sweet spot for the middle revs.


Also, generating domestic power with a heavy duty alternator while motoring will improve the overall efficiency of a mechanical drive engine. My alternator uses 6 horsepower, added to what the propeller is using.



A fixed speed diesel generator will get into much worse territory as it modulates power output without modulating RPM. A variable speed DC generator will be much better in that regard, but if undersized it will still be operating a great deal above the ideal regime so outside of the sweet spot.



This is just not an advantage of series hybrid.




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Yes you can, it's the USE that allows you to change the engine. One has to idle but not too fast AND also produce a certain amount of power at cruise continuously, and also sell it's max HP to the buyer. The other has one target only, efficent power continuously. A generator engine is NOT the same as a drive engine.

Sure, but generators in hybrid drive systems are still subject to varying power requirements, so you still have to modulate power output. Also, what do you achieve with this "efficient continuous power", in real numbers? Speaking from real experience now -- I have a high quality, heavy duty, very expensive low speed AC generator. At full output, it burns 2.5 l/h to produce 6.5kW of electrical power. That's 320 grams of diesel per kW/h of electrical power. That's about 15% worse than fuel consumption of my main engine even with a fixed prop, and interestingly corresponds exactly to the fuel consumption hit from diesel electric compared to mechanical drive for my friend's expedition vessel. It's about 25% worse than the fuel consumption with my variable speed prop.


That doesn't include power lost in converting back to mechanical energy with the motor, but the figure for mechanical drive doesn't include losses in the gearbox, so it's roughly apples to apples.





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Originally Posted by bridaus View Post
Unfortunately I don't know the two engines ssmoot compared so I'm not sure if you could use the more efficient one in a drive application or vice versa. Still the point remains that you CAN and WILL choose a different more fuel efficient engine for the generator and use it ONLY in it's fuel efficient regime because it CAN be used at it's most efficient. The direct coupled engine CANNOT be used at it's most fuel efficient, because it is unable to run at one speed! USE matters.

This is fallacious -- running a diesel engine at one speed is quite on the contrary -- WORSE. You will get better fuel consumption if you can vary the speed according to power demand to stay in the better part of the fuel map.



If you look at the actual specific fuel consumption figures of different diesel engines, you will see that those used in gensets and those used as main engines generally have the same specific fuel consumption according to the technology used. Turbo improves specific fuel consumption, and common rail even more. There is no magic diesel used in gensets.



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BTW, no one is here to insult what anyone is doing, but I find that sometimes people take new technology as a personal affront to the way they've been doing things. Nothing is wrong with what we are doing now, in fact hybrid solutions are very expensive right now, and therefore it's truly debatable whether it's worth it to choose this in a new build. Whatever you have now, it's right for you and none of this discussion makes it "wrong".

This is a good comment, and important to the discussion FWIW, I never took anything posted here by you or anyone else as any kind of insult. That would be really silly. I think most people here are just genuinely interested in how the different systems work and what is the real truth of the matter. It's a good discussion, and thank you for your contributions to it.






Fuel maps from Morgan's Cloud, "Understanding An Engine Fuel Map", https://www.morganscloud.com/2015/06...gine-fuel-map/
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Old 13-12-2018, 08:21   #1625
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Re: Oceanvolt Hybrid Motor

If you're building a hybrid, why in the world would you use a fixed speed AC generator? A permanent magnet DC generator is far lighter and much more efficient in converting motion to electricity, not to mention fully capable of operating in the best part of the engine map.
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Old 13-12-2018, 08:34   #1626
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Re: Oceanvolt Hybrid Motor

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Originally Posted by OldMan View Post
Post #1596

43' Sailcat
3GM30 F or C. The fuel graph you gave us was the DIN B rating (pleasure) not A (commercial), was that on purpose?

If this manual matches yours, then we're on the right track. More in a bit.

http://www.jeanneau-owners.com/Manua...e%20Manual.pdf
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Old 13-12-2018, 09:13   #1627
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
3GM30 F or C. The fuel graph you gave us was the DIN B rating (pleasure) not A (commercial), was that on purpose?

If this manual matches yours, then we're on the right track. More in a bit.

http://www.jeanneau-owners.com/Manua...e%20Manual.pdf

FC


The output graph shows the A de-rating.
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Old 13-12-2018, 09:20   #1628
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Re: Oceanvolt Hybrid Motor

Correction: I see your graph shows DIN A and B, and the prop curve interacting with A, so we'll assume A for now also.

Boat: 43' Sailcat
Engines: 2x 3GM30 @17.7 kW "continuous" (from manual I found, but I fear is a newer engine than yours)

I'm still suspicious of Yanmar's ratings, either they have magic or they have caveats. Either way, I'll take the specs as word for now.

This means maximum continuous power is 35.4 at 3400 RPM. Can you reach 3400, and if not, what's your highest RPM that you have reached with WOT?

Also curious as to your normal cruise speed, but just curious, not needed because nothing to compare it to...
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Old 13-12-2018, 09:43   #1629
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Dockhead View Post
There are three flaws with this:

1. Who said anyone is limited to a fixed pitch prop? Lots of us, including me, have variable pitch props. You don't need to spend $30 000 on a hybrid system to use your diesel engine in its ideal regime, or close to it.
Fair, I've admitted I'm not a prop expert. Can you actually load the engine at low RPM's effectively enough to get it in it's most efficient sfc at cruise?


Quote:
Originally Posted by Dockhead View Post
2. Who said your hybrid system will be capable of keeping the engine in its ideal regime? A fixed speed AC generator will be worse at that than even a fixed pitch prop and mechanical drive -- because you can't even vary RPM with varying loads. It's true with series hybrid you can supplement generator power with battery power for short term high power requirements, and that is a genuinely valuable feature for sure, but the benefit of this is mainly in being able to reduce the size of the main engine, making it cheaper and lighter. You won't get a dramatic improvement in fuel consumption because you STILL have to modulate power with varying power requirements, so you will STILL be using the diesel at different loads, not all of them right in the sweet spot. Especially if it's a fixed RPM AC generator. But even a variable speed DC generator, which you are undersizing compared to the engine you would be using in a mechanical drive system, will be operating a lot over 80% output where fuel consumption is worse. So it is not only underloading diesel engines which leads to worse efficiency.
You missed the multiple times I said DC generator running at a fixed load and rpm at it's most efficient. Even if it has to be oversized, because that is not what matters, what matters is sfc.


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3. You are greatly exaggerating the fuel consumption hit even of a fixed pitch prop. Here is a typical small diesel fuel map:

You will see that at no time at typical operating speeds is the engine operating at as much as 20% less than ideal regime. A variable pitch prop easily pushes the curve right up into the sweet spot for the middle revs.

Also, generating domestic power with a heavy duty alternator while motoring will improve the overall efficiency of a mechanical drive engine. My alternator uses 6 horsepower, added to what the propeller is using.
These graphs have big holes in the middle, look a bit handmade. Not sure where the blog you reference got them, but seems there's a missing circle, looks too big compared to the graphs I've seen. Additionally, every engine is different, so we'd have to pick some really common ones and compare those. Am I reading right that those are for 100kW engines? Might explain the lack of precision. This isn't easy.


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A fixed speed diesel generator will get into much worse territory as it modulates power output without modulating RPM. A variable speed DC generator will be much better in that regard, but if undersized it will still be operating a great deal above the ideal regime so outside of the sweet spot.

Sure, but generators in hybrid drive systems are still subject to varying power requirements, so you still have to modulate power output. Also, what do you achieve with this "efficient continuous power", in real numbers? Speaking from real experience now -- I have a high quality, heavy duty, very expensive low speed AC generator. At full output, it burns 2.5 l/h to produce 6.5kW of electrical power. That's 320 grams of diesel per kW/h of electrical power. That's about 15% worse than fuel consumption of my main engine even with a fixed prop, and interestingly corresponds exactly to the fuel consumption hit from diesel electric compared to mechanical drive for my friend's expedition vessel. It's about 25% worse than the fuel consumption with my variable speed prop.

That doesn't include power lost in converting back to mechanical energy with the motor, but the figure for mechanical drive doesn't include losses in the gearbox, so it's roughly apples to apples.

This is fallacious -- running a diesel engine at one speed is quite on the contrary -- WORSE. You will get better fuel consumption if you can vary the speed according to power demand to stay in the better part of the fuel map.

If you look at the actual specific fuel consumption figures of different diesel engines, you will see that those used in gensets and those used as main engines generally have the same specific fuel consumption according to the technology used. Turbo improves specific fuel consumption, and common rail even more. There is no magic diesel used in gensets.

Again, DC with fixed load, you are bringing in valuable experience for a different discussion, but not this one.


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Originally Posted by Dockhead View Post
This is a good comment, and important to the discussion FWIW, I never took anything posted here by you or anyone else as any kind of insult. That would be really silly. I think most people here are just genuinely interested in how the different systems work and what is the real truth of the matter. It's a good discussion, and thank you for your contributions to it.
Thanks. It's important to be constructive to have good conversations that you can learn from. Otherwise people stop listening and contributing.
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Old 13-12-2018, 09:48   #1630
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Re: Oceanvolt Hybrid Motor

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Boats don't have regen braking which contributes a lot to auto hybrid efficiency.
I'm going back to lurking for awhile, but I can't resist.

This is a myth. It absolutely does not "contribute a lot" in the way a layman might think of.

It's a generator connected to a shaft. It doesn't matter if it's an axle or a crankshaft.

Say it's 70% efficient. That power gain only applies to kinetic energy. Not all the energy you put into the system to get where you're going. If you accelerate up to 50MPH, then apply the brakes immediately, you'll get the exact same amount of power as if you'd driven on the highway for 100 miles with no braking, and then had to stop at a light.

Not only that, but because it's not 100% efficient it's always more efficient to avoid braking entirely. Which is why hyper-milers try to take curves without slowing down, and coast between lights to avoid using brakes.

Regenerative braking is more efficient than using friction brakes since friction brakes are 0% efficient. But there's nothing more efficient than not braking in the first place.

But wait you say, the Prius gets better City mileage than Highway! Isn't that due to regenerative braking?

The short answer is no. Just think to yourself, how often do you have your foot on the brake pedal vs the accelerator? Sure there's some benefit to it, but nowhere near the 25% difference you might see on the Munroney. You might find this thread of hyper-miler record holders enlightening: https://priuschat.com/threads/top-20...olders.112709/

Compare it to a Chevy Volt with a much larger battery. The Volt is also a hybrid. It also has regenerative braking. It's also direct driven when on engine power. But the city mileage advantage disappears entirely. Or take a look at my wife's Chrysler Pacifica PHEV. It actually gets significantly better highway mileage when the battery is depleted because it's more efficient to run off generator power than use regenerative braking.

If you've got an electric motor moving the wheels, regenerative braking is a no-brainer feature for boosting fuel economy in the city to reasonable levels. But it's not magic. It's actually more efficient to not waste that power in the first place.

It's exactly the same as traveling in a flat vs hilly area. Just because you get to coast "for free" down the hills doesn't make up for all the extra fuel you're burning to climb them. That would make your vehicle a perpetual motion machine if it were true.

If you could drive everywhere at around 45MPH without any stopping or hills, you'd get the most miles out of the vehicle. If you need further proof than me saying so, just read the accounts of hyper-miler record holders and their tips for maximizing mileage.

So if you're going to move a vehicle with electricity, then a boat, running at hull-speed (avoid wasting energy climbing up and down "hills" as much as possible) on passage is actually pretty close to the best case scenario for electric propulsion.
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Old 13-12-2018, 10:12   #1631
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Re: Oceanvolt Hybrid Motor

Agree regen isn't a lot, I think the big difference with boats vs cars is that boats can't really coast, the "friction" is incredibly high. That is why they are the last thing for hybrid to show it's efficiency at... more like a plow truck than a Prius.

PS, how dare you take us away from our currently scheduled programming! Talk about herring!
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Old 13-12-2018, 13:10   #1632
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
Agree regen isn't a lot, I think the big difference with boats vs cars is that boats can't really coast, the "friction" is incredibly high. That is why they are the last thing for hybrid to show it's efficiency at... more like a plow truck than a Prius.

PS, how dare you take us away from our currently scheduled programming! Talk about herring!
Except that "regen" under sails, doesn't require "braking" on a sailboat, just a little detail, a way to transform wind energy catch from the sails, that is all
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Old 13-12-2018, 13:32   #1633
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Re: Oceanvolt Hybrid Motor

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Except that "regen" under sails, doesn't require "braking" on a sailboat, just a little detail, a way to transform wind energy catch from the sails, that is all

But it is braking....the power comes from somewhere, no magic! The regen prop in the water is drag on the boat. If the boat could use that power for faster speed, then yes, it's "braking".


SVReality reported a .5kt slowdown to realize 400W of regen.
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Old 13-12-2018, 13:36   #1634
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Re: Oceanvolt Hybrid Motor

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Correction: I see your graph shows DIN A and B, and the prop curve interacting with A, so we'll assume A for now also.

Boat: 43' Sailcat
Engines: 2x 3GM30 @17.7 kW "continuous" (from manual I found, but I fear is a newer engine than yours)

I'm still suspicious of Yanmar's ratings, either they have magic or they have caveats. Either way, I'll take the specs as word for now.

This means maximum continuous power is 35.4 at 3400 RPM. Can you reach 3400, and if not, what's your highest RPM that you have reached with WOT?

Also curious as to your normal cruise speed, but just curious, not needed because nothing to compare it to...

I doubt I can get to 3400rpm....I know I can get to 3200, maybe 3300, fixed props. Target cruise speed is 7-7.5kts @ 2700-2800rpm.


FWIW, that model engine ceased production in 2005 (I think), mine are the last vintage of that model.
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Old 13-12-2018, 13:41   #1635
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Re: Oceanvolt Hybrid Motor

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I think the big difference with boats vs cars is that boats can't really coast, the "friction" is incredibly high.
That's true in boats vs cars, but drag is a constant in electric vs diesels so I can't come up with a good reason you'd (the proverbial "you", not personal) include it in efficiency calculations.

But the same fundamentals apply. Coasting (net-zero power input/output) is actually inefficient over distance since in order to coast you had to build up an amount of potential energy greater than the energy you would've expended with a constant force.

So ignoring friction, this is basically a gravity battery, which can be pretty efficient, but still in the range of 70% to 90%. Better to just not spend that 30% to 10% if you can avoid it.
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