DAVE HALLIDAY wrote in a message to JIM DUNMYER:
 DH> Most of the recent large ships are diesel-electric.  Works
 DH> great since it allows the diesel to run at constent RPM, you
 DH> derive ships power from the same engine ( no need for
 DH> another engine for the genset ),  infinite control over the
 DH> speed and torque delivered to the props,  when cruising, you
 DH> can usually shut one engine down and run both props from
 DH> the other engine ( makes periodic maintenence a lot easier
 DH> too ) 
 DH> One added advantage is that since the engine isn't delivering 
 DH> power directly to the prop, the engine/generator assembly can 
 DH> be floated on shock absorbers - the vibration and noise is 
 DH> significantly less. 
 DH> The technology has been in place in locomotives for 20 years
 DH> - it took a while to show up on ships but it is proving to save 
 DH> fuel, offer better control and be easier to run.
 DH> Check any of the commercial marine magazines - Professional
 DH> Mariner is a good place to start - National Fisherman is
 DH> another one although it covers more of the small boats (
 DH> too small for these systems to be economical )
Now I'm wondering just what it is that makes such a setup impractical below a 
certain size...
It seems to me that the answer to this one is the key to why we're not seeing 
more in the way of hybrid vehicles,  for one thing.
Way back when if you had a "shop" with "power tools" it usually involved an 
engine of some sort,  driving one or more shafts which were often mounted up 
near the ceiling,  and power was transferred to various items of equipment 
via long,  flapping,  leather belts.  The engine could have been steam or 
whatever.  My grandfather had at one time a shop which used a similar setup 
driven by a big electric motor,  probably a 2 - 5 HP unit.  The last memory I 
have of this is seeing that motor sitting off in a corner,  and noting that 
the various tools now each had their own smaller motors,  that having become 
much more practical in the intervening years.
I suspect that we'll probably be seeing a similar transition in this stuff 
before too much longer.
email: roy.j.tellason%tanstaaf@frackit.com 
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