Hi Eric,
Thanks for another thoughtful response. I'll be going "all in" to some extent, but with the mindset of not really having expectations. Yes, I do have projections, and hopes... no expectations though.
One interesting boat design that I came across today is called the Aqua Casa. Honestly I had seen it before today, but I had discarded it relatively quickly because it doesn't suit me for one reason or another. Here's a link:
http://www.berkeley-engineering.com/AquaCasaHouseboat.html
The interesting thing to note is the full rocker. Very similar to my own, though the curve is shallower relative to the length of the hull. I understand that what I'm building is indeed untested and experimental, but the general design is not without precedent.
One thing is becoming clear out of all this... I don't want to start off with a production electric outboard. They're too expensive and not powerful enough. They also don't seem very customizable... if I find that a huge 16" prop turning at 800 rpms is the best fit for my application, there aren't any that would accommodate that.
Cheers,
-keith
--- On Tue, 5/8/12, Eric <ewdysar@yahoo.com> wrote:
> 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
>
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