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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