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Old 30-07-2008, 06:33   #31
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7 days in a row
- that's one hell of experience

it should go easier with cats, these are light and lively (not in harbours, though )
our boat is rather heavy and was initially designed as a motorsailer
so we installed a FisherPanda electric shaft of 28kW - now trying to
defeat battery problem

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Old 30-07-2008, 06:36   #32
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Originally Posted by Curmudgeon View Post
What is the diesel fuel usage with a diesel engine running a generator, which supplies juice to an electric motor that turns the prop, vs. a system where the diesel engine turns the prop directly when there isn't enough juice for the electric motor or more power is needed?

In a true hybrid system you would need some sort of clutch to switch between the two engines.
we consume 3 liters per hour for an 7 knot speed or 1 liter for each 2.3 NM traveled
and that is not take into account any solar or wind recharging.


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Old 30-07-2008, 06:39   #33
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electric propulsion requires smaller engine (because of much higher torque irrelevant to RPMs approx 40% less powerful engine necessary), no gearbox, shorter propeller shaft (if any) etc etc

so fuel consumption in any case will be less than for conventional drive

and: why should 2 engines be necessary ?
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Old 03-08-2008, 02:57   #34
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I do see more benefits of the hybrid argument for mid size power Cats that hang close to shore, at least on some points. Running several, smaller generators, that no longer need to be located in the engine room(s) appears to me to have an advantage over two large diesels (with their associated running gear) sucking fuel every second the boat is underway. System monitors can fire up or shut down as many gens as necessary as power demands increase or decrease. And it matters not which gens run, as both motors can be powered from any, or even a single power plant. It even has the benefit of built in redundancy as losing a generator for whatever reason means only giving up a bit of top end speed.

Obviously, I understand any weight savings by ditching those big twin power plants will more than likely be negated with the increased number of generators and increased battery capacity, but still... having smaller, gens that can come online as needed, running at optimum RPM the whole time instead of constantly throttling up and down seems like it has to have some benefits. The least of which being fuel savings.

Hypothetically speaking, if I were currently in the market for a 40'-50' power Cat and could haver one built and equipped from the get go with multiple generators and dual elect motors, at a reasonable cost over a conventional setup, then I think I'd seriously consider taking a closer look at hybrid propulsion.


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