Glenn asked: “But which would be more efficient, turning the motor faster or slower with more resistance?”
Judging efficiency just by the prop efficiency, it’s a no-brainer: Bigger prop, not too high in pitch, turning slower.
That produces the least amount of slip.
But then there’s the gearing and the motor/controller circuitry.
Gearing losses are probably not a variable factor to consider between options—they’re likely a fixed loss including some stiction & dynamic aspects.
But at the motor/controller end, the discussion needs to turn to the manufacturer specs.
The controller will have a range of voltages (i.e. motor speeds) that it will accommodate for regen.
Below some threshold, its boost capability can’t produce a high enough charge voltage to send current to the battery.
And so, speed is important.
It may be that regen doesn’t even kick in until 4kts of current drives the prop in most cases.
But so you get regen with your prop at say 5kts, but want more.
You decide to go with a bigger, higher pitch prop to try to capture more energy.
The prop does end up capturing more energy, but its speed slows down below the system’s threshold for efficient regen and output ends up being lower than original. Your $200 investment in a new prop was a waste.
-mt
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> OOPS.I meant to say: Since the power is proportional to the speed cubed, the
> prop driving 10knots of current will transfer substantially MORE power than
> if it is "driven" by the water with the 5knots of water stream current in
> regen (assuming efficiencies were the same both ways, which they aren't).
>
> -mt
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