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post #9 of Old 04-26-2008
MedSailor
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Quote:
Originally Posted by Rockter View Post
There is no way on this earth, with earthly laws of physics, that a fuel-driven electric generator, feeding mechanical energy to a generator, then electrical energy to a motor, and from there mechanical energy to a prop will EVER out-perform the direct drive-to-prop diesel in the first place. There is just no way that can happen.

What am I missing here?

If you want something quiet to get you in and out of harbour, then perhaps, but this stuff must not be advertised as being capable of prolonged motoring into a tide, or headwind, or chop, or all three.

It won't cut it, unless you have a very big battery bank indeed, and a lot of time to charge it.

For example, 25 hp (shaft power at the prop shaft) for 6 hours is about 112 kWh delivered, and probably about 1/4 more than that is needing storing to deliver on it. They will not try to deliver that at 12V, but, if they did I calculate the energy storage to be (corect me if I am wrong)...

112 kWh * 1.25 = 140 kWh = 140,000 Wh = 140,000*3600 = 504 MJ

.... call it E.

If you are to find E from your battery bank, then...

E = current*voltage*time

E = I*V*t

Make the product of I*t the subject...

I*t = E/V

Say, for argument, your power is delivered at 12 volt...

I*t = 504,000,000/12 = 42,000,000 amp.second

= 11,666 Ah

My current house battery is 275 Ah.... that is about 1/42 of what would be needed for 6 hours motoring.

That was 6 hours motoring, and I'd need 11,666 Ah to do it, discharging the batteries to nil to do it.

My current tank capacity will keep the motor running for about 30 hour.

Pls correct me on this one there guys. Did I get it wrong?
If this is true than why are almost all cargo ships and ALL locomotives diesel/electric and have been for 50 years?

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