On Sun, 16 Dec 2007 04:35:35 +0100, Heikki wrote:

Richard van den Berg wrote:

Regular outboards do have a fair weight/hp compared to e-motor and
batteries. The only thin you have to worry about is fuel. Or how did you
plan to fill your batteries?

Oh, I was planning to have a diesel engine (and a generator) running most of
the time to provide the electricity. The idea was to be able to place the
generator engine where I wanted it, and the propelller(s) and the driving
engine where they would be most useful. Instead of a solid shaft, I would
have flexible cables in between. I could run it on the batteries for a
minutes, if I needed extra manouvering, but in most cases, the power would
come from the generator. Also, I was hoping that the electric propulsion
would be smaller and lighter, so it would be easier to lift out of the
water when going by sail...

- Heikki


First of all, "there is no magic". If it takes, say, 10 H.P. (at the
propeller) to move your boat then regardless where you get it will
always require 10 H.P (at the propeller).

Second, the more devices you add between the prime mover and the
powered device the more losses you will have.

So, if you install a diesel engine, a generator, a battery bank, an
electric motor, cables and finally a propeller you are building in
losses at every stage between the diesel engine (prime mover) and the
propeller (powered device).

So, your 10 H.P. (at the propeller) plus losses result in the need for
a larger engine - say 12 H.P. Plus added initial cost, added problems
and added maintenance costs.

Unless you are talking about a really large vessel I don't believe
that there will be any advantage and probably several disadvantages in
using a diesel-electric drive.


Bruce-in-Bangkok
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from address for reply)