Hi Julian,
If the motors are overloaded with the 23 x 22 props I'd have them repitched before I resorted to reducing their diameter. You want to keep all the disc area you can.
Assuming that the props will be either bronze or Nibral, a prop repair shop should be able to take up to 2" of pitch out of them.
-Tom
--- In electricboats@yahoogroups.com, Julian Webb <julian.proto@...> wrote:
>
> Hi Eric
>
> - have them As no prop man would guesstimate speed for my boat, maximum efficiency
> was all I could head for that they seemed able to calculate to.
>
> - I know I'm a bit on my own when it comes down to it, just didn't want to
> be at the "bleeding edge" and be first-in-my-class but hey someone has to
> do it as they say.
>
> - I'll publish/post all my results and hope I don't have to either new
> props made or the proposed ones turned down (the only cheap mod I can think
> of) as they are costing me £1000 each!!!
>
> - I know I could have had off-the-shelf guesses way cheaper but I thought
> if I went to a "proper" prop maker I would get what was optimum for my
> boat............... time will tell I guess, "a fool and his money" as they
> say.
>
> Cheers, Julian
>
>
> On 27 March 2013 18:46, Eric <ewdysar@...> wrote:
>
> > **
> >
> >
> > Hi Julian,
> >
> > My point is that your suggested prop may be the most efficient, but it
> > won't deliver the boat speed that you said that you wanted for your stated
> > motor speed. It's all about compromises. I just wanted to warn you of what
> > you are signing up for.
> >
> > Personally, I prefer a boat that has enough power to motor at at least 1kt
> > above my personal cruising speed. It's up to you to pick that speed for
> > your boat. My ketch can motor electrically at full throttle at 6kts, (1/2kt
> > faster than it could with the 12hp diesel) and my cruising speed is usually
> > somewhere between 4.5 and 5kts.
> >
> > My suggestions were based on these personal preferences and I tried to
> > make that clear. This is largely conjecture on my part, I don't know of any
> > other conversion like yours. That said, you get to be judge of whether you
> > have faith in my reasoning, I have already included why I have made the
> > suggestions that I have.
> >
> > Eric
> >
> >
> > --- In electricboats@yahoogroups.com, Julian Webb <julian.proto@>
> > wrote:
> > >
> > > Hi Eric
> > >
> > > - I get that torque is flat....
> > >
> > > - As I was scaring prop makers away, all I asked them to do in the end
> > was
> > > to design/make me a LH and a RH prop that were the *most efficient *for
> > motors
> >
> > > that I had and it's the prop maker has spec'd the 500RPM as being the
> > best
> > > match for the 23 x 22 props. which he said were the most efficient given
> > > they are the largest I can swing under the boat leaving 15% clearance.
> > >
> > > - While you won't lose me on anything from the shore power inlet to the
> > > motor coupling, please give me an honest opinion on what you think would
> > be
> > > the best prop, as it's the one part where you can lose all your hard work
> > > in the rest of the system.
> > >
> > > - At the moment I calc at 6 knots I will run at 1/2 the Diesel
> > consumption
> > > she used to on her old Diesel engines but not if the props are wrong, and
> > > as custom made props are expensive in this part of the world I really
> > need
> > > to get it as near to right as I can.
> > >
> > > Thanks again, Julian
> > >
> > >
> >
> >
> >
>
>
>
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