Hi Kerry,
You're absolutely correct. Diesel-electric has been used for many decades and has proven to be more efficient than diesel alone. But there appears to be a problem of scale. They are used in locomotives, cruise ships and submarines. I'm not aware of any successful production examples of a diesel-electic drive in a vessel/vehicle that weighs less than 100 tons. With some of the large power yachts, i.e. bigger than 100', fuel consumption is a serious concern, and yet they haven't taken advantage of this "proven" technology.
And then there is the question of how much more efficient. If you're burning a gallon per minute (about 700hp at 25% thermal efficiency), then a 20% increase in efficiency would be worth doing. This could save 100 gallons in 8 hours of operation. On the other hand, your boat should burn less than 1 gallon per hour at displacement speeds, so a 20% increase in efficiency will save about 2 gallons on a 10 hour cruise.
I think that you might be on the right track with an electric motor to alternatively drive the boat through the regular drive train will give you more of the advantages and less of the drawbacks to both types of drives.
My personal opinion is that even that may not be worth the trouble on a boat as small as yours. But that's just my opinion.
Fair winds, and smooth seas,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "kerryfenn" <camillekerry@...> wrote:
>
> Eric,
> thanks for your frank reply. I was under the impression that a small efficient, constant RPM generator / electric combo would be more efficient than a conventional diesel engine, especially if the generator could run the motor directly somewhat like a locomotive(!). I also assumed that the generator would be heavily sound shielded and tucked away somewhere unobtrusive leaving deckspace unencumbered by engineboxes ect. I also like the option of having a quiet generator for AC power. I can see that the system would easily get complicated especially when you start talking about DC generators. Maybe I would be better going with an inline electric motor on the shaft of a small conventional diesel and a big battery bank also driving an inverter for ac. I guess this is what they had on Dragonfly (slowboatcruise.com). At least this way if you need power to get out of trouble you've got the diesel.
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