My guess is that the prop wasn't being properly loaded at that speed, Denny, hence the same current for a given speed. Thrusters are designed to operate at very low speeds, less than 1kt, so the blade pitch at 3kts would have been way outside the design spec.
I've found that a ducted prop needs more blade area at the tip to work efficiently, along with slightly less twist, as the duct allows the blade tips to do useful work (normally thrust right at the tip of a blade is zero, due to spanwise flow and tip vortex generation).
--- In electricboats@yahoogroups.com, Dennis Wolfe <dwolfe@...> wrote:
>
> My second electric launch used an epic whisper outboard which is
> basically a huge trolling motor. It has a slightly cut down 6 blade
> Vetus bow thruster prop in a 12" dia kort nozzle. I could not measure
> any difference with / without the nozzle on my light easily driven boat.
> Even at 3 or 4 mph the amps to get that speed was the same. No
> difference at top speed of 8 mph either. It did make a huge difference
> at zero speed. With it I could power load the boat almost all the way
> onto the trailer. Without it there was only enough thrust to move it
> about half way up.
>
> Denny Wolfe
>
>
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