Diesel Electric Propulsion

[valhalla360]

"Horsepower is a misleading term, especially in marine engines. A diesel's horsepower rating is not a measured quantity, but a calculated one. It only applies at a specific rpm, usually around 2500-2800 for a typical marine diesel. At the low rpm used during most sailboat operations, actual diesel horsepower is much less than advertised. More importantly, diesel torque is much less as well."

2500-2800rpm is exactly what most cruising diesels run at. Once you get the boat up to speed, it just stays there in the ideal range.

Also torque is what determines if you can turn the propeller. HP determines how fast you can turn it.

[ranger58sb]

Originally Posted by Hyprdrv

EVTV Motor Verks Store:
Jack Rickard is a known guru for electric systems for cars and is just now getting into small classic speed boats. Worth looking at some of his TV productions. By the way that price includes battery straps but not the shipping from his door to yours.

Originally Posted by Hyprdrv

Ranger,
For an 800AH pack for your house bank you would need 16 180AH LP's. There is a quite long string on LP's for a house bank here at CF. Some very good info if you can wade through it all.

Thanks, Steve, Yeah, I've tried to understand everything in that thread... with mixed results (I often can't tell fact from opinion, when it's new topic for me).

Here, I don't quite understand the math. You're saying 16 times 180 Ah is somehow gonna equal 800 Ah?

-Chris

[socaldmax]

Originally Posted by valhalla360

Please enlighten us. This subject was already discussed a few pages back and no one came up with an explaination for how electric motors break the laws of physics.

HP is HP. It is defined the same regardless of where power is derived from. Saying it's complicated is dodging the question. HP is what determines cruising and top speed. The instant torque from zero RPM will result in better acceleration but it won't get you to a higher speed.

The closest someone came was the ability to use larger propellers but to achieve any significant increase in efficency would require masive propellers and you could achieve the same effect with a diesel by running it thru a reduction gear to boost the torque and turn the same giant propellers. Even with massive propellers, you aren't going to get anything close to 2.5 times the efficency.

I believe you are confusing hull speed with electric motors having some special ability. In calm conditions, it doesn't take a lot of power to get a boat up to hull speed. Most boats are outfitted with more HP than is needed to reach hull speed but when you try to do hull speed and fight a strong headwind you need that extra HP if you expect to maintain hull speed or punch thru waves. The standard approach with early electric powered boats is to keep costs down by accepting that you won't be able to maintain hull speed. You could achieve the same thing by outfitting 12hp diesels.

I am happy to learn. On another thread I was corrected on my understanding of how GPS calcualtes speed and I learned from it. If I am missing something, I would open to learning but so far no one has come up with an explaination and your description fits perfectly with the limitations of a hybrid system runnng smaller HP motors.

Yes, HP is HP.

Except when it's measured at a different point in the power band under different conditions.

Internal combustion engines are measured by their max. torque on an engine brake dynamometer. Max hp is calculated using torque x rpm / 5252. The torque peak may occur at say 1800 rpm and the hp peak is usually considerably higher rpm, perhaps 3200 or 4300.

They are tested without any accessories, which draw power.

An electric motor is measured by it's max torque, which is available throughout it's rpm range. They don't drive any accessories like a water pump or 180 amp alternator. (That 180 amps is not free power.)


By the time you bolt a 35 hp diesel engine up to a transmission and slap a couple of water pumps on it and an 180 amp alternator, you're probably getting 15 shaft hp at 1800 rpm - optimal cruising rpm. If you can get a copy of the dyno curve for the engine, you can get an idea of the engine's hp at 1800 rpm, then start subtracting the accessories, transmission losses and what is left is what you really have to propel the boat.

Take a 12hp electric motor that doesn't redline at 3400 rpm with no accessories on it and doesn't need a transmission because it produces max. torque from 1rpm through 10,000 rpm and you'll get virtually the same performance out of it.

The real measure of power is torque. That's why diesels have been favored over gas engines for boat propulsion since the beginning. They produce more torque at a lower rpm at a much lower brake specific fuel consumption rate (partially because diesel fuel has more BTU in it than petrol) and last longer due to heavier construction and lower rpms.

Torque is the real value that we should be comparing between one motor and another. Torque is what propels the big diesel trucks towing 80,000 lb loads, and that's why you always see diesel engines in towing situations, whether they're light, medium or heavy duty trucks.

From every website that I've seen - forestry, woodworking, boating, electric cars, agriculture, etc, the conversion factor everyone is using is 1 hp electric motor = 2.5 or 2.75 hp diesel engine.


I can understand the desire to have power in reserve for those emergency situations where winds and tides are fighting you. You could easily opt for a 15 or 18 hp motor instead of a 12 hp, that should give plenty of extra power. Remember, the electric motor can rev much higher than the diesel, if necessary.

Don't forget, a lot of people are discovering they can swing a much larger prop (limited by hull clearance) so you'll see a performance increase from that as well.

[socaldmax]

Originally Posted by Arthur Garfield

Hp is Hp
Watts are watts
Kw are Kw

"eHp" are Hp generated by electric though are still equal in force/power to mechanically generated Hp.

There is the conversion ratio difference of KW to Hp.
1 hp = 0.745699872 kilowatts
1 kilowatt = 1.34102209 hp
A person is able to talk themselves into anything !
Any talk of "eHp" somehow more powerful than Hp is entirely magical thinking !

I am all for "Ep" but ICE/carbon fuels still rule but not for much longer.

All the Best

You were correct, up until this part.

ICE and electric motors are rated differently. They put an ICE on an engine dyno with no accessories and measure the torque directly, then they calculate the hp from that.

Add on the accessories, transmission losses and you will get nowhere near the rated hp.

Sure, some that is drivetrain loss, but don't underestimate the power robbed by driving a water pump (or two) and a high power alternator, in the case of a boat.

Electric motors are rated at their continuous use power rating, less than their actual max rating and can drive the shaft directly if desired, there's no need to run it through a transmission unless you want to multiply the torque, which works even more in it's favor since it has a much wider rpm range than any diesel ever built.


All of the experts in the field of replacing ICEs with electric motors state that the ratio is between 1:2.5 to 1:2.75.

[socaldmax]

I think most people are approaching this from the wrong angle. They want to generate enough energy to store in a battery bank to run an electric motor. That's highly inefficient and the most expensive approach.

I think your battery bank should run your house loads and that's it. Power it from solar, or the genny, or a smaller dedicated genny or ideally a combo of the above.

The most efficient engine on the planet is also the largest diesel ever built and it's used in supertankers and cargo ships.

The railroads all use diesel electric hybrids because it's most energy efficient for their situation. They can run the diesel alternator at a fixed rpm, rectify that AC output to DC, invert that to 3 phase AC, direct drive the wheels and still save fuel over a diesel engine changing rpms to accelerate the load.

The most fuel efficient car in the world is a VW diesel-electric hybrid, which is about 3x more fuel efficient than their TDI series, for which they are well known as being fuel efficient.

Railroads squeeze every last penny to make a profit, if a diesel engine alone was the most efficient mode, then they wouldn't bother with the whole alternator /rectifier /inverter mess. They also only use batteries to start the diesel, it's not part of the propulsion system.


If one ran a diesel 16kw 3 phase generator (alternator, actually) at say 440v it could be designed to run at the most efficient rpm and consume as little as .75 gal/hr while driving 2 15 hp 3 phase AC permanent magnet motors. I'm not positive of the costs, but it might actually be cheaper than 2 brand new 35 hp Yanmar diesels with sail drives and a 6kw genny for the house loads. (In the case of a catamaran.)

For a monohull, change the hp numbers accordingly to give you the same hull speed and size the generator to power the electric motors and charge the normal sized battery bank. You're still relying on 1 diesel engine if the wind dies, so no real loss in reliability.

In the case of the catamaran, you're giving up the redundancy of having 2 diesel engines, if one dies, you could still move pretty well on the other. If the D-E hybrid generator dies, well you're back to sails and waiting for a breeze.

By eliminating the huge battery bank, you've cut the cost way down to comparable or possibly even cheaper than 2 diesels with saildrives.

Keep in mind, motoring is supposed to be your backup propulsion, not your primary, despite what 500 mi of headwinds might have made it feel like...

[med]

The reason railroads use diesel electric is not because of efficiency.

It is because electric motors have their highest torque at zero rpm. Which is exactly what you need to start moving a long heavy train. It is much easier to manage than any system with clutches and gears. Diesel hydraulic has also been used.

You don't need high torque to start a boat moving.

Nigel Calder looked at hybrid propulsion for boats here:-
The Science of Hybrid Propulsion: Part 2 | | PassageMaker

The conclusion was the gain in efficiency of the diesel engine running the generator by running it at its most efficient specific fuel consumption point was not sufficient to counter the losses and inefficiencies of the electrical system - but that it was a close run thing.

However, if you use a more modern common rail electronically controlled diesel engine, then you get close to the optimal specific fuel consumption over a wide range of operating conditions ranging from about 20% to 90% load. You can get the information needed to compare vs Nigel Calders data from the John Deere web site.

I.e. a modern properly size diesel engine will get you more miles per gallon of fuel than a hybrid set up under the same conditions (wind, current, speed).

But it is a close run thing. (Which is why the railroads are happy with diesel electric and do not go to the trouble of adding a direct drive through a gearbox for cruising speed).

So, I would save the wind generator and solar panels for charging the house batteries and use a properly sized diesel engine as all the big cargo ships do.

Those ships a run to get the maximum payload from A to B at the least cost. The major cost is fuel. So it is not by chance that the have the most efficient diesel engines going.

It is interesting comparing the specific fuel consumption figures of the engine in Emma Maersk against a 80HP engine for a yacht.

So use a modern common rail, turbo charged, electronically controlled diesel engine which is sized such that you are loading it to at least 20% at cruising speed and you will be very very close to optimimum fuel consumption and have plenty of power in reserve for when conditions are less optimimum (or for going faster).

[Stumble]

God, not the stupid train thing again. Trains use diesel-electric for the simple reason that they have 8 powered wheels. Read that again, 8 drive wheels. The transmission losses are grater than the diesel-electric losses so it works for them. If you had 8 props under your boat using diesel electric would work just as well. To my knowledge EVERY diesel train ever built has used diesel-electric because the transmissions for direct drive would be rediculious.

If you read Calder what he says is that at very low speeds D/E can work, but the crossover speed even with purpose built (ie non-commercial) generators is no higher than 5.5kn or so. At speeds below this there is some efficiency gain to be had by going D/E but the problem is that at these slow speeds a diesel uses pretty small amounts of fuel.

Worse, if you size the electric system for these conditions you wind up with a boat that can't propel e boat when you really need it. The only way to get around this is to add a massive generator which destroys the efficiency of the system anyway.

In other words, if all you want is to get in and out of a harbor then D/E works. If you want to be able to motor at typical cruising speeds for hours or days at a time then it doesn't.

[nimblemotors]

Whew, glad that is settled. Now can we go back to discussing why people need portable generators instead of running their diesel engines to charge their batteries or heat hot water, or run the microwave, or the A/C.

Originally Posted by Stumble

In other words, if all you want is to get in and out of a harbor then D/E works. If you want to be able to motor at typical cruising speeds for hours or days at a time then it doesn't.

[med]

Originally Posted by Stumble

To my knowledge EVERY diesel train ever built has used diesel-electric because the transmissions for direct drive would be rediculious.

Diesel-Hydraulic is also used.
E.g. Vossloh G1700 BB - Wikipedia, the free encyclopedia

[socaldmax]

Originally Posted by med

The reason railroads use diesel electric is not because of efficiency.

It is because electric motors have their highest torque at zero rpm. Which is exactly what you need to start moving a long heavy train. It is much easier to manage than any system with clutches and gears. Diesel hydraulic has also been used.

You don't need high torque to start a boat moving.

Nigel Calder looked at hybrid propulsion for boats here:-
The Science of Hybrid Propulsion: Part 2 | | PassageMaker

The conclusion was the gain in efficiency of the diesel engine running the generator by running it at its most efficient specific fuel consumption point was not sufficient to counter the losses and inefficiencies of the electrical system - but that it was a close run thing.

However, if you use a more modern common rail electronically controlled diesel engine, then you get close to the optimal specific fuel consumption over a wide range of operating conditions ranging from about 20% to 90% load. You can get the information needed to compare vs Nigel Calders data from the John Deere web site.

I.e. a modern properly size diesel engine will get you more miles per gallon of fuel than a hybrid set up under the same conditions (wind, current, speed).

But it is a close run thing. (Which is why the railroads are happy with diesel electric and do not go to the trouble of adding a direct drive through a gearbox for cruising speed).

So, I would save the wind generator and solar panels for charging the house batteries and use a properly sized diesel engine as all the big cargo ships do.

Those ships a run to get the maximum payload from A to B at the least cost. The major cost is fuel. So it is not by chance that the have the most efficient diesel engines going.

It is interesting comparing the specific fuel consumption figures of the engine in Emma Maersk against a 80HP engine for a yacht.

So use a modern common rail, turbo charged, electronically controlled diesel engine which is sized such that you are loading it to at least 20% at cruising speed and you will be very very close to optimimum fuel consumption and have plenty of power in reserve for when conditions are less optimimum (or for going faster).

Railroads brag that their system is 4-10x more efficient than semi trucks for hauling freight. At the very least, they lead one to believe it's due to their diesel -electric hybrid design.

Most small yacht diesel engines are not common rail or turbo. When a previous discussion on turbocharging came up, the vast majority of boat owners felt that a turbo drastically reduced the life of the engine.

As the owner of a Duramx diesel, I can tell you that since common rail systems run at up to 36-39K psi of fuel pressure, fuel cleanliness is of much greater importance than in traditional injection systems. Injector reliability still isn't where it should be. Even the newest Bosch injector designs in the new Duramax and Cummins engines are going to require expensive periodic injector replacements.

I'm glad you guys provided a link to Nigel Calder's work. He's trying to charge batteries to run the motors, but it' a great source of data. Here is an interesting 2 paragraphs that seem to support my position in terms of catamarans.

Every non-engine kilowatt-hour (kWh) of energy reduces the average fuel consumption rate for propulsion and house power. In certain niche applications, it is possible for the entire energy budget to be met from non-engine sources. An example of this is short-haul ferry boats that can plug into shorepower between trips, storing sufficient energy in the batteries to complete the subsequent trip. Catamarans with high sailing speeds and intermittent propulsion needs are another example. These boats can produce sufficient energy through regeneration to meet normal propulsion needs; they also benefit from having a large surface area available for solar power.

In both these examples, a serial hybrid installation would, in effect, operate as an electric boat, with the generator held in reserve for emergency purposes or longer trips that exhaust the batteries. The lower the generator-run hours in relation to the propulsion hours, the lower the average fuel consumption rates. These rates are likely to be well below those in an optimized conventional installation—even if the fuel consumption rates when the generator is running are higher than in the conventional installation.

He doesn't mention initial cost of the serial hybrid system, I'm sure that would scare most people away.

This statement is also very encouraging, it echoes something I posted a couple of weeks ago - I can't wait to see some diesel powered fuel cells in the 85% efficiency range.

A potential breakthrough technology that will fundamentally change this situation, when and if it matures, is reformulating fuel cells—fuel cells that will run directly from diesel, but with energy conversion levels from diesel to electricity well above those achieved by generators.

I think it can be designed using waste heat to preheat the fuel, high pressure nozzles to atomize it into a mist then find a suitable catalyst, hopefully something like the Bloom Box, to convert it directly to DC current. Emissions will be far lower than any ICE, virtually zilch.

[Stumble]

Originally Posted by med

Diesel-Hydraulic is also used.
E.g. Vossloh G1700 BB - Wikipedia, the free encyclopedia

Fair enough, thanks for the correction. But the point is the same, to eliminate the hugely complicated transmission that would otherwise be required.

[Hyprdrv]

Ranger asked,
"Here, I don't quite understand the math. You're saying 16 times 180 Ah is somehow gonna equal 800 Ah?"


You need 4 batteries to get a 13V pack at 180AH per pack. These are wired in series so the pack batteries are multiplied but the total AH stays the same. You then wire 4 packs together in parallel to multiply the AH to get 720AH but the V stays the same, 13V. 4 cells to a pack=13V, 4 packs to get the 720AH=16 cells(batteries)
Hope that helped,


Steve in Solomons MD
Lagoon 410 S2E

[Maine Sail]

Originally Posted by Hyprdrv

Ranger asked,
"Here, I don't quite understand the math. You're saying 16 times 180 Ah is somehow gonna equal 800 Ah?"


You need 4 batteries to get a 13V pack at 180AH per pack. These are wired in series so the pack batteries are multiplied but the total AH stays the same. You then wire 4 packs together in parallel to multiply the AH to get 720AH but the V stays the same, 13V. 4 cells to a pack=13V, 4 packs to get the 720AH=16 cells(batteries)
Hope that helped,


Steve in Solomons MD
Lagoon 410 S2E

With LFP parallel cells first to attain capacity the wire in series...

4P4S
4 In Parallel & 4 In Series

[ranger58sb]

Originally Posted by Hyprdrv

You need 4 batteries to get a 13V pack at 180AH per pack.

Originally Posted by Maine Sail

With LFP parallel cells first to attain capacity the wire in series...

4P4S
4 In Parallel & 4 In Series

Ah, got it. Hadn't understood the 4X part of the equation.

-Chris

[Hyprdrv]

I had the pleasure of having Nigel Calder and Dave Tether on Electra Glide a number of years ago(4Y?) to review some changes and upgrades that had been done as well as discuss the technology. At the time LP batteries were just an idea. Understand I felt like my head was going to explode but overall Calder liked the system and Tether saw that the "improvements" made sense. What most of the concern about Electric Drives has been around the energy storage, batteries. With the advancement of cells using Lithium over the last few years and the continued development with other materials there has been ideas for energy storage that could give us batteries that will out distance the use of fossil fuels.
I never planed on going around the world when I bought EG, I planed on cruising the Bay and hopefully doing the Carib. and learning from the system I have. I've been pleased with the way things are and think that the majority of boat owners who day sail and cruise the coasts could benefit from the systems available today. The way some people talk you would think that there isn't any wind beyond the site of land and that most sailors head out to look for dangerous weather. Believe me the wife will pull the plug and load the guns if I don't get back in. In both conditions if I needed to run the genset to make power to run my props I could care less as to how much fuel I use as long as I had enough.
The 410 had the engines under the stern bunks. One of the complaints was the engine noise. With electric drives I hear a hum and the waves slapping the hull. I have no fuel or oil smells, the compartment stays cool, and the bilges are clean enough to eat off of. I don't have sail drives to mess with either.
Pretty much everything is a plug and play. Batteries(power sources) to controller to motors. All power makers are sent to a main distribution point and sent to the batteries or devices, looks like a big J-box with disconnects. Other than that the wiring is simple if you break it down to components.
I joined the string because I believe there was no one else who was running Electric. I really don't care if you decide to or not but think that it's worth looking at in any case. I like looking outside of the box, thinking of ways to improve the system, and eek out another mile or 2.

Steve in Solomons MD
Lagoon 410 S2E