Join Date: Sep 2006
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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 08:03 PM.