Sounds like you need to run a much lower pitch prop. If it is
cavitating, you are just wasting energy. Are you running it in a tunnel?
Pitch? Diameter?

Karl Townsend wrote:
My apple water bin dump uses a .5 horse 3 phase 220 VAC motor attached by
pulleys and belt to an outboard motor prop in a tube to pump water. Maybe 1"
head at 100+ GPM. I just measured the current draw on this motor at 1.5 amp,
2.0 amp, and 2.2 amp with a clamp A-meter.

Its a 1725 RPM motor with 2.2 reduction to the prop, so the prop turns about
800. Its a NOISY operation. The prop cavitates and pulls air even with all
the deflectors I can install to stop the vortex. (I've only lived with it
since 1988)

I bought a prop that will throw a guestimated 3 times the water per
revolution. There's no way to know until its installed. I have the physical
room to change the pulleys and get a 3.5 reduction or about 500 RPM. That's
most likely too fast and too much water.

OK, now to the question. Will installing a VFD and running the motor at 50%
speed have a good chance at working? Or, do I need a larger motor and VFD?
I want to move the same amount of water.

Karl