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post #16 of Old 10-20-2006
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Originally Posted by Faster
...As an auxiliary it's attractive from a noise/vibration perspective but realisitically to produce as much power as a conventional diesel drive the generator will need to be the same size or larger. So you won't get away with a smaller "cheaper" engine this way. ...
Faster, despite your intuitive analysis, in the trial systems fielded some innovators have been able to downsize the diesel by about 25% as a generator yet achieve the same speeds on small yachts when compared to direct diesel drive systems. I will try to find some references on that but I know I've seen that figure frequently in the literature. In the case of the Lagoon recently at the Annapolis show they were in fact able to replace the two conventional diesels with a net smaller diesel generator.

Achieving those downsizing results is dependent on very proper engineering so that the efficiencies of the diesel-generator can be best exploited while the direct diesel approach does have it's own inherent inefficiencies. One interesting aspect is that efficiency improvement can be harvested with the generator with the ability to use a larger prop which practically speaking is not an option with a direct diesel drive.

The best tutorial I've seen to date is on the Glacier Bay website: It's pretty heavy stuff but I think it really does relate the complex variables involved. With all of the factors involved it suggests to me that one can't easily look from the outside of the two types of systems and make an assessment of which will be more efficient. Rather, the engineering must be done to make such a determination.

Originally Posted by Faster
...Maybe the fuel cell idea will come to a more practical level of technology in the nearer future.
GM and Chrysler have bet the farm on it. We should know how that works out in about 5 more years.

-- neal

For my headstone:

If I'd only listened to those guys about that wing keel...
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