Diesel Electric Propulsion

[cwjohm]

Comparing equivalents is not simple. It depends on the torque curves of the motors in question.

Torqueedo make this pretty easy nowadays, as they specify HP equivalents in their motors.


According to their website a 40HP equivalent is U$20K for the motor and $20K for the batteries. For a cat you need two plus the equivalent KW generator to run one motor when you need it. Let us say 25Kw at least which will be around U$40K.


Total install cost U$120K just for the equipment. All of the wiring and controls is extra. Compare this to U$40K for diesels with simple wiring and controls.


BB's treatise on full lifecycle costing is accepted, as is his generosity in being happy to pay the difference as his contribution to global warming. Most of the rest of us, selfish bastards one and all, will pocket the difference.

[nimblemotors]

HP is HP, but HP = Torque * RPM, and a diesel has a narrow band of RPM that it can produce the HP. Whereas an electric motor can produce HP all over, from 1/10th to 10x its 'rated' HP and at different rpms.

For a boat that is pushing through the water at hull speed, the engine and prop and gearing can be designed so it uses the engine in the narrow rpm band.
And they will get better fuel economy this way.
But this why they don't do well as generators when anchored, because they won't be loaded like they do when pushing the boat at hull speed.
So almost every boat has another engine for a generator.

So the engine is optimized for passage making to save a few dollars,
but is poorly designed for everything else.

So how much time do you spend making a passage under power vs everything else?
A cargo ship we know the answer.
A daysailer we have a good idea.
A cruiser?

Like the airplane video, if you free the boat from having a big heavy engine that must be coupled to a prop, you open up the possibilities. Like a bow thruster, point me to the diesel powered ones. Or having propulsion on all six point of a trimaran, or ??? Innovation, or save a few dollars on fuel today?

[BigBeakie]

Originally Posted by cwjohm

Comparing equivalents is not simple. It depends on the torque curves of the motors in question.

Torqueedo make this pretty easy nowadays, as they specify HP equivalents in their motors.


According to their website a 40HP equivalent is U$20K for the motor and $20K for the batteries. For a cat you need two plus the equivalent KW generator to run one motor when you need it. Let us say 25Kw at least which will be around U$40K.


Total install cost U$120K just for the equipment. All of the wiring and controls is extra. Compare this to U$40K for diesels with simple wiring and controls.


BB's treatise on full lifecycle costing is accepted, as is his generosity in being happy to pay the difference as his contribution to global warming. Most of the rest of us, selfish bastards one and all, will pocket the difference.

CW,

It's actually better news than the figures you've used, but watch this space.

[cwjohm]

It's actually better news than the figures you've used, but watch this space.

I will watch it whilst I am alive. I cannot make any guarantees after that. If it is of any comfort when my cruising days are finished and I am getting around in a mobile unit, it will definitely have electric motors.

[BigBeakie]

Originally Posted by cwjohm

I will watch it whilst I am alive. I cannot make any guarantees after that. If it is of any comfort when my cruising days are finished and I am getting around in a mobile unit, it will definitely have electric motors.

Aw, CW you are in great nick. You'll have EP in your TAG, mark my words

[valhalla360]

Originally Posted by socaldmax

I don't mind discussing things, but if you're going to continue to dispute facts, like the definition of power, or gas engines being able to tow just as well as diesels, then I'm going to start asking that you provide sources for your information, because it's contrary to what I've learned.

If you look at your first graph, the torque curve is very flat. So unless you want to be pedantic, there is very little difference in torque at peak efficiency vs peak hp. Where the electric motor has significant advantage is in the below 1000rpm range. No one suggested running at redline was most efficient but it's there if you need the power and you can run just below redline for hours if needed. As long as you don't make a regular habit of it, no significant harm is likely to the engine. Unlike the example where you can run an engine at 200% of rated power for 5min (30 sec? whatever it was).

I said, they COULD build gas engines that will put out the torque of a diesel. I also said why they don't. For trucking, the cost equation still favors diesel over gas (Not so much for pickups or boats but that is more about marketing).

Here is the definition of power:

Power is the work per unit time, given by:

P = T * w,
where P is power, τ is torque, ω is the angular velocity, and * represents the scalar product.

Dynomometers do not measure hp, they measure torque, and hp is calculated from the torque measurement. Why? Because torque is the measure of power, and hp is how much work is done over time.

Thank you for proving my point. To calculate HP (diesel or electric), you need both torque and angular velocity. If you put a 10hp diesel against a 10hp electric and run them both at 10hp, if the electric motor is putting out twice the torque, the angular velocity must be half (or you could put the diesel thru a reduction gear and get the same angular velocity).

In the context of a diesel-electric, you are basically replacing any transmission losses with energy conversion losses (mechanical to electric back to mechanical)

In a displacement application, HP is still HP and the boat doesn't care where it came from.

[valhalla360]

Originally Posted by cwjohm

Comparing equivalents is not simple. It depends on the torque curves of the motors in question.

Torqueedo make this pretty easy nowadays, as they specify HP equivalents in their motors.


According to their website a 40HP equivalent is U$20K for the motor and $20K for the batteries. For a cat you need two plus the equivalent KW generator to run one motor when you need it. Let us say 25Kw at least which will be around U$40K.


Total install cost U$120K just for the equipment. All of the wiring and controls is extra. Compare this to U$40K for diesels with simple wiring and controls.


BB's treatise on full lifecycle costing is accepted, as is his generosity in being happy to pay the difference as his contribution to global warming. Most of the rest of us, selfish bastards one and all, will pocket the difference.

Torquedo does not make it easier. They are trying to sell a product and are making the same mistake several people on this thread are making but most likely they are doing it intentionally to make their product look more favorable.

[valhalla360]

Originally Posted by nimblemotors

HP is HP, but HP = Torque * RPM, and a diesel has a narrow band of RPM that it can produce the HP. Whereas an electric motor can produce HP all over, from 1/10th to 10x its 'rated' HP and at different rpms.

For a boat that is pushing through the water at hull speed, the engine and prop and gearing can be designed so it uses the engine in the narrow rpm band.
And they will get better fuel economy this way.
But this why they don't do well as generators when anchored, because they won't be loaded like they do when pushing the boat at hull speed.
So almost every boat has another engine for a generator.

So the engine is optimized for passage making to save a few dollars,
but is poorly designed for everything else.

So how much time do you spend making a passage under power vs everything else?
A cargo ship we know the answer.
A daysailer we have a good idea.
A cruiser?

?

The problem is with a hybrid system, you still have the same problem. It's massively oversized for house loads at anchor. Now if you went with a twin generator system (small one for at anchor and big one for motoring) that would be more efficient except it would be even more expensive than the hybrid system and the weight might eat up some of the efficiency gains.

The days of running the engine to top of the batteries seems to be fading as solar panels get better and cheaper, so the vast majority of the time engines will be used to push the boat along at cruising speed, so the diesel can be optimized to serve that purpose except for a few minutes entering or leaving harbor.

[BigBeakie]

Originally Posted by valhalla360

Torquedo does not make it easier. They are trying to sell a product and are making the same mistake several people on this thread are making but most likely they are doing it intentionally to make their product look more favorable.

Wow Valhalla, that's big call!

I guess you are not aware of who is involved at Torqeedo, nor their reputation in technical circles in things electric! In other words, not to put too fine a point on it, their CREDIBILITY.

So your ignorance is forgivable, but slagging a manufacturer certainly raises issues about your credibility, unless of course you have any facts to support your case.

Which particular mistake are they making, just to be clear???

[valhalla360]

Originally Posted by BigBeakie

Wow Valhalla, that's big call!

I guess you are not aware of who is involved at Torqeedo, nor their reputation in technical circles in things electric! In other words, not to put too fine a point on it, their CREDIBILITY.

So your ignorance is forgivable, but slagging a manufacturer certainly raises issues about your credibility, unless of course you have any facts to support your case.

Which particular mistake are they making, just to be clear???

I never take marketing material at face value. Only the ignorant do. As long as you are willing to live with the costs that come with ignorance, you are forgiven also.

Gurus, technical circles, etc... is usually code for the marketing department twisted the facts to make their case. Usually the avoid outright lies but if you read the details, you find caveats and exceptions to cover them when they provide information that an unbiased source would disagree with.

The mistake is the claim that electric HP is somehow magically more powerful than any other HP. (keep up with the conversation).

[cwjohm]

Torquedo does not make it easier. They are trying to sell a product and are making the same mistake several people on this thread are making but most likely they are doing it intentionally to make their product look more favorable.

No, this is not correct. They did get into a bit of a bind in that they were quoting maximum hp, and then people made assumptions that based on electric torque curves they could get away with half the hp of a diesel engine. Of course this was toxic from a marketing point of view as the engines did not generate the hp required.

What they are doing now is quoting equivalent diesel hp so there is no confusion. The calculations are available and quite valid. This enables and apples for apples comparison.

The Gunboat Deep Blue solution is quite clear and costing baselines established. Obviously Gunboat is getting discounts but it is still 3 times the price of diesels fully equipped.

Of course a threefold affect will be in play

Price of Electric motors will reduce
Battery Densities will increase
Generator costs will decrease

At some point in time there will be a crossover. We are merely arguing the timing.

I suspect I will be pushing up daisies before this crossover occurs but one can live in hope. As an alternative maybe I can make enough money so that like the Gunboat owners an extra U$100K or so is neither here or there.

[leftbrainstuff]

Originally Posted by Hyprdrv

No Valhala Electric motors do not put out the same HP as diesels, or 1 to 1. The common formula to somewhat equalize electric motors to diesels is 1 to 2.5 meaning for every 1 EHP you need 2.5 DHP do to efficiency of the Emotor. So my 12HP Emotor is equal to a 30HP Dmotor.
I've had this conversation before with my Nabors at the dock. A 40ft mono has a top speed of 8 knots which it seems is the typical speed of most boats of any size based on their motor size. If they hit a short steep wave of 4 feet with head winds their pretty much in the same range I am when I do the same. A "standard" diesel running at 2400 RPMs (typically their max) can throttle up higher but so could I. In my case the torque will remain the same with higher RPMs to the props giving me more speed but my limit is the Amp Draw from the batteries or genset. The genset is limited by it's max output of 110A or in actuality 80A do to limits of an overdraw safety switch. Electric motors are far more efficient than diesels across the board. As far as fighting head winds and waves we both loose something.


Complicated is subjective. My wife's sawing machine to me is complicated. 8O)


Steve in Solomons MD
Lagoon 410 S2E

A DC motor puts out max torque from 0 rpm. When comparing to a diesel you need to pick the torque at the rpm of interest. This will let you compare apples to apples.

In all cases, except at peak torque a diesel will need to have a higher torque rating than a DC motor being compared. This is because the diesel rating will be a peak torque reading. If the peak torque is peaky and not flat then this value may not be achievable in practice.

Its also worth noting that the efficiency of most DC motors is vastly superior to the 30% efficiency of a diesel's ability to utilise the energy in the fuel. Using a diesel generator to generate the electric power for a DC motor cancels out this benefit.

Also you need to pick steady state torque for an electric DC motor. Torque based on peak in rush current has no practical use in a discussion about boat propulsion. Brochure figures can be very misleading. A graph of the dyno'd torque is needed in both cases.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[valhalla360]

Originally Posted by cwjohm

No, this is not correct. They did get into a bit of a bind in that they were quoting maximum hp, and then people made assumptions that based on electric torque curves they could get away with half the hp of a diesel engine. Of course this was toxic from a marketing point of view as the engines did not generate the hp required.

Thank you. My point exactly and supports not trusting marketing literature at face value. I have no doubt they knew what they were doing but the marketing department over sold the capability and the engineers failed to reign them in.

What they are doing now is quoting equivalent diesel hp so there is no confusion. The calculations are available and quite valid. This enables and apples for apples comparison.

Certainly, you can develop an equivalency but the 1 eHP equals multiple diesel HP theory goes out the window if you do for a displacement vessel applicaiton. (automotive applications would have a different equivlency due to different power needs)

The Gunboat Deep Blue solution is quite clear and costing baselines established. Obviously Gunboat is getting discounts but it is still 3 times the price of diesels fully equipped.

Of course a threefold affect will be in play

Price of Electric motors will reduce
Battery Densities will increase
Generator costs will decrease

At some point in time there will be a crossover. We are merely arguing the timing.

I suspect I will be pushing up daisies before this crossover occurs but one can live in hope. As an alternative maybe I can make enough money so that like the Gunboat owners an extra U$100K or so is neither here or there.

I agree, we are arguing timing. The problem is, electric motors, batteries and generators have been around for 100yrs and we are still no where close them being a viable alternative (assuming similar capabilities and cost).

I don't believe it is the electric motors or the generators that we are waiting on. They are already well developed and there isn't a lot of room for improvement without getting exotic. It's storage that is limiting the adoption of electric motors. The day someone comes out with a battery (or alternative energy storage system) that holds even 1/4 the power of an equivilent volume diesel and the cost is in line with diesel fuel, the diesel engine is history. Within 2-3yrs no new boats will offer diesels and except for historically accurate refurbishments, all repowers will be electric motors.

[DeepFrz]

I notice that the new Common Rail engines from Yanmar have a very flat torque curve compared to older engines. I would assume that is the same for all Common Rail engines.

[socaldmax]

There have been fairly recent development in electric motors that make them more efficient, compared to even 10 yrs ago.

The railroads went from AC motors to DC motors and now they're using 3 phase AC permanent magnet motors which are smaller, more powerful and more efficient. AFAIK, no one is using these in a yacht application.