On Wed, 08 Jul 2009 19:22:34 +0700, Bruce In Bangkok
wrote:

Your preliminary comments are correct :-)

I'm interested in your reasoning for the electric drive as it seems to
present no advantages to have a diesel fueled generator which charge a
set of batteries to provide power to an electric motor to turn a
propeller.

Given that any mechanical or electrical device will have some losses
it would seem that there will be less efficiency then a system that
connects the diesel engine directly to the propeller rather then going
all round Robin Hood's barn, as it were.

Cheers,

Bruce

Be glad to explain my reasoning. First, you are correct in that is is
less efficient, maybe by as much as 15%. Don't forget though, that the
clutch is going to give some losses, more so with a hydralic one.

But. In my case at least I think overall it would be better. Not a
major thing, but it would give me a bit more of stowage space because
the generator would be moved back from where the engine is and the
electric motor would take little room and be back where the clutch is
now.

I've built a couple electric cars, bikes and trikes and a motorcycle
so I'm quite familiar with the beast :-)

The electric on battery only would give 3.5 to 4 kts for several
hours, assuming I don't add any batteries. It would be used mostly for
less than an hour at a time, probably more like a few minutes to 15 or
20 minutes. The solar/wind should be able to put this back in a day or
two or three in most cases. If not, there's the generator. Assuming
the generator is not needed, a plus is no heat to make its way into
the cabin. Efficiency is really not a factor. You might as well say
it's infinity percent or totally free sine the solar/wind is
eventually putting it all back.

For longer runs, which do happen occasionally, the electric motor
would be run directly off the generator, like a train diesel
locomotive or hybrid car. This would give 5 to 6 kts, depending on
generator size, for as long as there's fuel. This mode would be where
the efficiency loss comes into play, but I feel it would be worth it
for the other battery mode. Again, this would be a fairly small part
of "normal" operation.

So there would be two motor circuits - one for pure battery and one
for generator. The pure battery would be simple, just inexpensive
"continuous duty solenoids" and maybe a couple big diodes for a
"rectactor" controller to series/parellel the batteries for 2 speeds.
You don't really need a "throttle" type controller for these lower
powers.

The generator ciruit would be simpler and cheaper as well. Instead of
a complex DC controller, SCR's can be used on the AC output, then
rectifiers to convert to pulsating DC for a true variable "throttle".

The trick is to match the prop to the motor. It would probably be
better to gear down to turn the prop slower. This could be a fairly
simple chain or notched belt drive.

So...

Mode 1, battery only, would be simple to use. No warming up the
engine, moving, cooling down and stopping the engine. Just flip a
switch and go. Most of the time the energy gets put back "free".

Mode 2, generator only, would be pretty much like now except burning a
little more fuel. Maybe. Maybe not. There are factors that could make
that up. Clutch efficiency on a "straight engine drive" and the higher
torque of an electic motor come to mind. Okay, there's got to be some
loss overall, but again I think it would be worth it having Mode 1.

The above is my opinion based on the calculations. It would work for
my cruising style, but maybe not for yours.

Rick