[Public-list] weight distribution and electric power

[J Bergquist]

Gordon-

I did the same math and came to the same conclusion. Why go to electric and
then install a generator? In fact, I looked at exactly the same ones...honda
air cooled gensets.

I could never quantify the drag of the water generator. There are no hard
numbers out there on it. It's even tough to compare apples with apples when
comparing diesel power and electric power, because the diesel gives up a lot
of its available power in losses, where the electric has much lower losses,
and generally more available power. By available I mean that the electric
motor has very different torque and power characteristics which make its
power more available.

It's a very touchy-feely thing, which is unfortunate. And it has a lot to do
with your expected usage profile and how long you expect to go before
selling. There are significant resale value implications.

At the end of the day, there is a lot more Q per pound in internal
combustion. But if you can deal with the lower Q value per pound, electric
can be pretty doggone nice. Simple. Quiet. No smell. Always ready to go.
Pretty slick...

Personally, I am very interested to see how Dan's project turns out. It may
work very well, in which case I'd say it might be something for others to
consider too. I just didn't have the guts to try it like Dan has. Let myself
be talked into sticking with internal combustion...a decision I half regret.


Later,

JB

On 9/29/06, Gordon Laco <mainstay at csolve.net> wrote:
>
> I did a bit of figuring on this issue back when considering an electric
> aux
> in my old boat.  The water generator is not an inconsiderable drag while
> sailing.  I fell back on looking at fitting a small Honda generator, which
> would have done a fine job but there I was back with gasoline but this
> time
> in addition to the extra batteries and lower thrust the e motor could
> deliver...
>
> Gord #426
>
>
>
>
>
>
>
>
> > I have no idea how Dan is planning to recharge while sailing, but solar
> > panels are not the only way to do this. 2 other examples are wind
> generation
> > and water turbine generation.
> >
> > Water turbine generation was used by Gelinas during his round the world
> > cruise. It basically uses a propeller as a turbine, connected to a shaft
> > which drives a generator. Since a motor and a generator are physically
> the
> > same thing, most electric motors can be used as generators, and in fact,
> > most electric launches are set up in exactly this way.
> >
> > Regenerative braking in hybrid cars works exactly the same way. This
> > technology is well established and frankly much older and more mature
> than
> > photovoltaic solar power.
> >
> > I don't know much about efficiency numbers, but if Dan figures he's
> motoring
> > for 15 minutes to a half hour to get out of the harbor, followed by
> several
> > hours of sailing, I am guessing that since the generator is running at
> least
> > 10 times longer than the motor (assuming 2.5 hours of sailing for every
> 15
> > minutes of motoring), he probably is not going to have a problem
> replacing
> > whatever juice he took out.
> >
> > Plus he'll have a sweet way to recharge his house batteries and replace
> the
> > juice taken out by his lights and refrigeration and electronics and
> whatever
> > else.
> >
> > I wouldn't use the system while racing, though...that pesky 2nd law...no
> > free lunches and all that.
> >
> > JB
> >
>
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