Hi Keith,
Yep, you're right. There is no such thing as an "ideal prop". You can confirm this by asking any propeller dealer for the specs on "the ideal prop" for a Catalina 30. I picked that boat because there are so many around, all of the critical information should be easy to ascertain. But even here, the correct answer would be "it depends". Even with a boat where there are literally hundreds of examples that can be considered virtually identical, different owners want different things out of their boats. More power to push against tides and weather, more miles per gallon, lower engine speeds to reduce operating noise, each of these goals can be optimized by a slightly different prop. Every prop is a compromise, it is up to the owner to figure out what is important. And after all of that, picking a prop is still a fuzzy science. Prop recommendations will only get you close, it's not uncommon for a customer to come back to their vendor to say that the prop didn't work out as planned and that they need something a bit ddifferent.
Now, do the same thing for a boat design that has never been built and use a drive system that has little hard performance data available to extrapolate projected performance from. You can use various spreadsheets available on the web to predict your performance, but be advised that I've seen variances greater than 35% away from those predictions for conventional designs, both for the worse and for the better. It's pretty easy to completely misjudge your requirements for an experimental design. That's why I suggested building the boat and collecting hull performance data using cheap used motors. At least then, you'll know a lot more about the power that your hull will actually need for safe navigation. It's just that I hate to watch somebody go "all in" on a completely theoretical design. That is a path that often leads towards unfulfilled expectations.
Good luck and keep learning.
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Keith Jacko <nrixez@...> wrote:
>
> Thank you very much for the details, Eric. When I get far enough to report real world numbers, I'll be sure to share.
>
> None of what is posted here gives an indication of an ideal prop size, btw. Perhaps there isn't really such a thing as "ideal prop size", although everyone seems to say "bigger is better". Maybe I'll have someone make me a 2' prop then just to see how it performs. ;)
>
> Cheers,
> -keith
>
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