Quote:
Originally Posted by totodog
I think I know what he's talking about.
One diesel engine would turn the electric motor and the propeller. The electricity from that motor would go to power the other electric, which was connected to the propeller, but the diesel on that side was off.
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Yes, but how does that save fuel?
The running diesel has to burn more fuel to run the alternator and charge
the battery. The electric motor can not possibly be more energy efficient
than the motor used to charge it.
If the diesels run most efficiently at 7.5 knots and hooking up the alternator
reduces speed by 2 knots, but running the other electric increases speed
by 1 knot you have lost 1knot of speed for the same volume of fuel burnt.
Why does the diesel lost 2 knots charging the battery, but the e-motor
only give out 1 knot? Because the alternator, rectifier and e-motor all
introduce additional inefficiencies in the energy transfer from fuel to
propeller.
The most efficacy way to use the diesel motor is direct to the prop shaft.
That way you only have the energy loss caused by the inefficiencies in the
diesel motor. If you instead transfer some, or all, of the diesel engine's
out-put through an alternator, rectifier, batteries and motor you introduce
many new inefficiencies that will result in less power per gallon of fuel.