[Public-list] weight distribution and electric power

[J Bergquist]

I also am looking forward to seeing the hard data.

In addition to Skene, there are a number of useful propeller design books
which contain information on the subject. Gerr's "The Propeller Handbook" is
a good basic reference. An excellent more advanced reference is "Marine
Propellers and Propulsion."

At the end of the day, it's not a very exact science for us, because the
wake is poorly understood. It's basically empirical and experience-based. So
without any experience (not many people are using water generators in our
kinds of boats), it's tough to know what to expect or what to design for.

later,

J

On 9/29/06, Gordon Laco <mainstay at csolve.net> wrote:
>
> Yes, very interesting topic.
>
> I used to teach at Georgian College's School of Marine Technology and so
> had
> a terrific library at my disposal.  It was fun trying to figure out hard
> numbers for the various options.
>
> With regard to the water generator, I used thrust figures for various
> revs,
> blade orientation, pitch, area, etc. and tried to work backwards to get
> figures for a water DRIVEN prop (as opposed to a water driving).  Blade
> area
> is key, and since you can assume that slippage will happen in a similar
> ratio to thrust producing props - the big problem is getting the revs high
> enough and with enough torque.  Skene's Elements of Yacht Design is a book
> with useful data on this topic.
>
> I too look forward to what our colleague comes up with in an actual test.
>
> Gord #426
>
>
>
>
>
>
>
>
>
> > 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
> >>
> >>
> >>
>
> _______________________________________________
> These businesses support your Association:
> http://www.alberg30.org/store/A30supporters.html
> Please support them.
> _______________________________________________
> Public-list mailing list
> Public-list at alberg30.org
> http://alberg30.org/mailman/listinfo/public-list
>

 1159543436.0