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  #21  
Old 04-26-2008
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Quote:
Originally Posted by Giulietta View Post
Look...this is what I do for a living...so in reality...writting in this thread would be working for me...and I only work if I get paid....sorry

So that was my contribution here...signing off.

In the mean time...I find some posts really amuzing.
I think your link to the benefit of Diesel/Electric drives has been a major contribution to anyone wanting to learn more. Thank you.

I just find some posts confusing.
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  #22  
Old 04-26-2008
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Arch...

You have got your head stuck up the wrong end of your digestive tract.

I will quote you here...

"As for the idea that it is better to have a diesel motor run a generator which then runs an electric motor for power, that is well over 50yrs old and is in common use every day".

Are you seriously pedalling the idea on this website that it is better to run a diesel engine, couple it to a generator (take the losses in generating power there), then cable the power aft (taking losses again), then covert the electrical power to shaft power via an electrical motor (taking losses again)... than to couple the diesel directly to the prop via a shaft? All those losses compound.

Is that what you believe?

Are you serious?

You don't need to be Einstein to kick that idea up the sexual organ.

No-one is denying the existence of diesel-electric systems, but they exist primarily because of the ease of transmitting power along a tortuous (or mis-aligned) paths, or to multiple motors (on mulit-wheel power vehicles, for example). They are NOT used for their efficiency, just like hydraulic systems are not either.

On a sailboat, and it's practical, it is far better to couple the motor directly to the prop via a shaft. I promise you that a diesel electric system will NOT be as efficient, because the combination of generator, cabling, and electric motor will not be as efficient as the shaft. The generator, and the motor will heat up and throw the energy into the engine room.

I have not seen a prop shaft heat yet, in 20 years.

This diesel electric idea, running off a big battery bank, simply cannot store enough energy. Certainly, the batteries can turn the prop for a while, but not for long.

If my calculations are correct above.... pls correct them if not so... then just one hour 25 hp net, will need a battery bank of close to 2000 Ahr (12V base line calculation), and run to exhaustion. What will that weigh? Where would I store it? What will it cost?

I'd sooner have my diesel, and its 30 gal tank. I reckon that's worth about 58,000 Ah, and about another 8,000 Ah in each of the ship's two Jerry cans. My ship simply cannot carry a battery that big to compete.

In the dead of night, into a headwind, and chop, with the wind rising, and a young crew looking at me for what to do next, I'll settle for that, and it's just a key fob away, it charges my ship's batteries when I start it, AND IT'S MORE EFFICIENT AT TURNING THE PROP THAN A DIESEL ELECTRIC WITH THE SAME PRIME MOVER BECAUSE I DON'T NEED A GENERATOR, CABLING, AND AN ELECTRIC MOTOR.

Last edited by Rockter; 04-26-2008 at 09:03 PM.
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  #23  
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Quote:
Originally Posted by Rockter View Post
Arch...

You have got your head stuck up the wrong end of your digestive tract.

I will quote you here...

"As for the idea that it is better to have a diesel motor run a generator which then runs an electric motor for power, that is well over 50yrs old and is in common use every day".

Are you seriously pedalling the idea on this website that it is better to run a diesel engine, couple it to a generator (take the losses in generating power there), then cable the power aft (taking losses again), then covert the electrical power to shaft power via an electrical motor (taking losses again)... than to couple the diesel directly to the prop via a shaft? All those losses compound.
You Einsteins seriously need to read more.

I'll just respond to that quoted part because like smarter people before me in this thread I've had enough.

Of course there are losses in such systems but it is when they add up to less that makes the diesel/Gens more fuel efficient.

A quote from the already supplied link:
To get started it should be acknowledged that placing a motor and generator between the propeller and diesel engine does indeed introduce new losses into the drive train. These losses can range from relatively minor to very significant and are directly proportionate to the efficiency of the motor, motor controller and generator. Different motor technologies and construction methods result in products of widely varying performance. Using a greater number of thin laminations will result in a more efficient, though more expensive, motor or generator than if they are built using fewer and thicker laminations. Similarly, saving energy in the controller means spending more on the electronic chips that control the flow of power.


Itís not only a matter of spending money, but also one of developing and applying the most appropriate technologies. Some motor designs are quite efficient at one speed/load condition but drop off quickly as soon as the speed or load changes. Others have a much flatter efficiency curve. The collective impact of these differences can be huge with real operational efficiencies varying from better than 98% to as low as 72% for motors and typically between 97% and 84% for generators. This means that for every 100 HP out of the engine you could obtain as much as 95 hp at the propeller shaft or as little as 61 HP. At the high end this compares favorably with the 3% to 5% loss typical of a mechanical transmission (although not all electric motors can be directly connected to the propeller shaft).


Considering these electrical losses, is it really possible to improve energy efficiency? The answer is clearly yes, so long as the basic efficiency of your motor, generator and controller is high. What you are relying on is that you can improve the efficiency of other parts of the system by more than the new losses you have introduced. Fortunately, if the electrical system losses are relatively low, this isnít too hard to do. It turns out that there are many limitations inherent in conventional direct diesel drive that waste fuel. By making more efficient use of the engine and propeller it is possible to more than offset the electrical conversion losses.


The foundation for this saving comes from the fact that, in a well-designed diesel-electric drive system, the power required by the propeller is "decoupled" from the diesel engine speed. In other words, in a diesel-electric system, the engine/generator could theoretically be running at full speed (100% output) while the propeller is only tuning at 50% of peak speed so long as the motor is sized to handle the power. Similarly, if the propeller were lightly loaded, the engine/generator might only need to turn at low speed to provide enough energy to drive the propeller at full speed. This means that diesel-electric systems can be much better at "self-optimizing" to accommodate varying loads than are conventional systems. At sea, load conditions change by the trip (number of passengers), by the hour (wind and tide) and by the minute (going up a wave or surfing down it). These variations provide a significant opportunity for fuel savings.



As for batteries being used, there has already been one post saying it can be done. Since many sailboats have no engine (gee I guess that too is impossible) it would seem that a trolling motor would be an an obvious improvement, but I guess not to some.

My professional associations would also suggest I charge for this.

Or are you guys just kidding? You must be joking, people cannot be that opinionated and ignorant at the same time.

HaHa you got me but thats the last time in this thread, try another.
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  #24  
Old 04-26-2008
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What about that Swiss (non-sailing) catamaran that crossed the Atlantic using (I believe) only solar power to drive electric engines? I believe that they covered the whole boat with solar panels and are now touring the states. The trans Atlantic trip was done to prove the concept although I know none of the technical details.
Are there commercial ships using the diesel-electric marine power set up that Giu/Alexa mentioned? If the big boys are using it already then it can't be too long before it comes into wider use.
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There is a difference in terminology here that probably creates some miscommunication.

When diesel generator drives electric propulsion, what we have is in essence another type of transmission - mechanical, hydraulic and sometimes electric. It has its advantages and disadvantages, I am sure.

This is not the same as true electric propulsion - which really isn't so much about the motor but about the fact that energy is stored not in a form of liquid combustible fuel, but in a form of electricity stored in a battery.

The former is a viable transmission option. The latter is not viable at the current level of battery technology.
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Old 04-26-2008
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There are only two kinds of electric propulsion.

1. Totally powered by renewable resources using the batteries as the storage.

2. Hybrid where mechanical means are used to generate electricity and charge the batteries - sometime in combination with solar, wind, turbine power.

There are no others.

The company in question - has very much the same mantra as Re-E-Power. And for further clarification - electric propulsion is usually defined as that powered by the batteries where a sail drive propulsion is categorized as being that which has mechanical assist from aux gen sets.
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  #27  
Old 04-27-2008
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Let's look at this from another direction - weight vs range.
So, my boat currently has an approx. 50hp (50kW) engine and a 50-60 gallon fuel tank (it's inside the keel, and I don't know for sure as I try not to go on empty, the fuel on the bottom is pretty nasty). 50-60 gallons of diesel (at 7 lbs a gallon) weight something like 350-420 pounds.

Now, the engine from E-POD system (they had a spec) provides an equivalent of 7-9 hp outboard (yikes) and has a max. continuous amperage of 170 amp (and recommended cruise amperage of 50 amp, which clearly would provde about 30% of max power, or 2-3 hp). It is also 24-48v, which of course makes a lot of difference, but let's assume 24v somehow (24v * 50amp = 1200 watt, or 1.2 kw or about 1hp, at 48v it's 2 hp - but hey, 1 hp is aplenty for a boat, right?).

Ok, so 50 gallons of fuel last me from 50 to 75 hours. Let's go with 50, just to give electric a headstart. We'll need 50*50 = 2500 watt-hours of 24v electricity to run this thing. Now, modern battery amp hour ratings are given at 20 amp draw (and go down with higher draw) but we'll assume the best. So, our favorite 6v golfcart dekas are 215 amp hours each. We would need 4 times each for 24v and then 12 times groups of 4 for 2500 watt hours. Total of 48 batteries. At 65lbs each, thats about 3000 lbs. I suppose if you replace the ballast with batteries that might just work 3000lbs may be a bit difficult to stow though, what with carrying each of the 48 batteries. Of course since you can't discharge the batteries all the way (unlike the fuel tank), you need twice as much - 100 batteries, 6000 lbs

Of course that just gave us a system that is 50 times less powerful (1hp vs 50). For more power, don't forget to multiply the battery count and weight times 50

With current lead-acid battery technology, electric propulsion is just not there. Anyone trying to sell it is either a crook or a nutcase.
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Old 04-27-2008
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I used to have an electric Ford Ranger available for my use (because everyone else hated it) that I drove whenever possible. Only had three drawbacks, the batteries, the batteries and the batteries. They were really heavy, discharged too fast even with regenerative set at max, and took 10 times as long to charge as they would run. Only repair for any breakdown (there were several) was a tow to Ford Motor Co., you'd get in and it was just dead. No way to troubleshoot or duct-tape a repair. Until we get giant Li-Ion laptop type batteries or dependable fuel cell I'll stick to diesel. If worse comes to worst you can always homebrew a little something that'll make it run long enough to get to sea.
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I will stick to my Volvo, shaft drive, alternator, and 30 gal diesel tank.

You are welcome to your revolution.

Last edited by Rockter; 04-27-2008 at 04:57 AM.
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This was actually a very informative thread. Not so much about technology but how it is perceived. Thanks.
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