Thanks for the tips Kevin!
2014-09-12 14:22 GMT+02:00 Kevin Pemberton pembertonkevin@gmail.com [electricboats] <electricboats@yahoogroups.com>:
Consider a Kort nozzle, It will also help with vibration caused by wash
hitting the hull. The nozzle also directs that water that is forced outward
into thrust making a more efficient system than just a prop by itself.
Originally the nozzle was developed to reduce canal erosion but it was found
to increase efficiency as well.
Kevin Pemberton
On Friday, September 12, 2014 10:26:33 AM you wrote:
> Absolutely.
>
> And the common boat has a prop and drive system that is very ineffcient.
> The desirable thing to do would be to go to a prop 2-3 sizes large than
> commonly used.
>
> The problem is you would need to change the driveshaft as well, as an
> efficient prop wont fit in the standard aperture.
> As such, this is almost never done.
> Also, large props are expensive.
>
> In normal boats (inboards) you have gearboxes that requite cooling, and
> large hot oil and hydraulic coolers.
> All the heat is inefficiency (as is all noise).
> Heat does not appear from zero - work and then friction creates it. All
> heat created is a loss vs. having that energy go to the prop.
>
> The driveline wastes about 1/3 the energy.
> The prop wastes about 1/3 to 2/3 the energy. Normal props are very
> inffefficient at most speeds.
>
> So, only about 1/6 of the energy actually goes to move the boat !
>
> This is illustrated by numerous conversions done with small engines, and
> or large props, where relatively tiny engines move relatively very big
> boats.
>
> On 11/09/2014 02:33, John Acord jcacord@gmail.com [electricboats] wrote:
> > From reading various sources it seemed that a larger prop turning
> > slower would give a more efficient transfer of the power.
> >
> > Also, I have heard that running the motors at lower rpm under load
> > results in undesirable heating, thus the choice of a higher gear ratio.
> >
> > I found a listing in the Michigan Propeller catalog showing that there
> > are some Evinrude & Johnson outboards with 2.42:1 gears. Since I am
> > starting from scratch, not having an existing outboard in hand,
> > thought I might look for one of those.
> >
> > thanks,
> > John
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Posted by: Bendik Vignes <bendik.vignes@yahoo.com>
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