Hmmm, I wonder what the answer is? On the face of it, there has to be a way to capture more of that kinetic energy. I've heard others say that turning the prop to generate electricity cuts speed by a half knot or more.
If you had a 100% efficient system (impossible, of course) that would mean that at the end of 12 hours of sailing you'd have accumulated enough in the batteries to drive the boat 12 hours at a half knot. Maybe 4 hours at one knot.
A 50% efficient system should give you half that.
The electric motor/generator is one of the most efficient machines around, so that's not the problem. Evidently, as you've suggested, the prop design is crucial. This is a subject I know almost nothing about.
I understand that electric motors have great torque; I'm guessing that it requires more torque to turn them than than the relatively slow moving water flowing past provides. Seems like there needs to be some way to reduce the load so the prop spins easier.
md
--- In electricboats@
>
> --- In electricboats@
> >
> > Randy,
> >
> > Don't overlook the possibility of recharging your batteries by capturing the energy of the prop's turning while you're under sail.
> >
> > md
>
> Actually - do. It doesn't work. On a good day, you'll maybe get another 10 minutes of propulsion out of it.
>
> Unless...you can actually fit a 20" prop - I am stuck with 13" max. But most boats in this size range will have that problem. The shaft-angle would have to be too steep to hang a (much) bigger prop.
>
> -Keith
>
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