Hi
Not really correct. For a given constant speed application diesel alone is
more efficient.
Diesel electric drives are used for controllability in electric locomotives
and ships that do a lot of port calls. On passenger ships and submarines
they are used because generating capacity is just as important as
propulsion. In the past they were also used as a gearbox because the gearing
for really large ships engines did not exist.
Now, the most efficient ships propulsion are very large direct drive
diesels.
In yacht sized power plants it would be very rare to gain efficiency by
adding an electric motor between the diesel and the propeller. Of course you
can have other valid reasons for doing so. Silent running. Weight
distribution, Regen etc.
-----Original Message-----
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
On Behalf Of Eric
Sent: Saturday, 23 July 2011 8:15 a.m.
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: Hybrid drive
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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