On Wednesday 19 January 2005 07:14, James Hebert wrote:

A fellow I met with a large (90-foot) "expedition yacht" told
me his arrangement was a single propeller shaft driven from the
main diesel engine, but also incorporating a hydraulic drive unit.
In the event of main engine failure, the two generators could be used
to turn the main shaft via this hydraulic coupling.

Many military vessels use diesel-electric drive, where the actual
shaft is turned by a very large electric motor. This allows
many coupling arrangements by electrical switching of the current
to the main motor, but this is generally too expensive for most
private yachts.

I figure he must be driving the generator on the main shaft as a motor
then? Interesting emergency solution indeed. But I wonder, what would
the power output of that 'engine' be and will be able to move you very far.

I'd love to get some real cost figures for a real electrical propulsion
system as that seems to do precisely what I am looking for.
Buy four or six cheap and small diesel engines to drive one electric
engine. First I thought that driving the engine indirectly in this way
would create some humongous losses BUT after some research I just did I
found that the losses due to the conversion from diesel power to electric
are no more than some 10% and even better that you more than make that up
by always running your (way cheaper) engines at much better load (60%)
by selectively switching off the ones you don't need. Of course that
load is much better for the engines too. So actually it turns out to
be cheaper to operate and gives truly amazing redundancy.
Installing some kind of battery (electric car? fuel cell?) might also
allow you to move without starting the engines at all and thus (if
for short spells with a battery) in total silence...
I am really excited about these possibilities! Problem is, nobody seems
to sell or install these things? And I *really* don't think this is a
DIY project... Perhaps the technology is still too new or not (yet?)
popular enough.