b504now,
You math look right to me and should get you on the water. I would try to make your motor mount in a way that you can try different ratios so that you can "tune" the system once you start operating the baot.
Fair winds,
Eric
Marina del Rey
--- In electricboats@yahoogroups.com, "b504now" <b504now@...> wrote:
>
> ok. Some better information. Now I am new to this game so any thoughts, help or fixes would be good.
>
> My prop is 10 1/2 dia with 13 pitch. I am not sure I want to go that way but lets start there. Oldish lower unit. My lower unit has a 7/4 ratio (drv Shaft to Prop) so my math works like this....
>
> If I want a cruising speed of 12 mph, 2 hr run time, at an efficiency of 50%, I'll need a prop speed of 1950 rpm. That translates to 3411 rpm at the drv shaft (allowing for gearing).
>
> If my battery bank produces 225 and operates to 40%, my run consumption needs to be about 1750rpm and based on the feedback, about 3.5hp, 67amps. (all 48v). So I will likely gear up 2/1 (emtr to drv shaft) which gets me to 3500. That seems close enough.
>
> everyone pick holes....I need all the help I can get.
>
> I also have built a few boats, both stitch and glue as well as traditional. But I just purchased a CNC machine capable of cutting 4X8 sheets. So my son's and my boat building is about to take a leap forward. The Sneakeasy will be the first one we do with CNC parts. (and also the first one my wife chose)
>
> Thanks
>
>
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