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post #23 of Old 04-26-2008
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Originally Posted by Rockter View Post

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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