Does a certain RPM range exist where a prop is usually most efficient?

I'm just wondering if there is an upper RPM limit where the prop thrust becomes decreased and pitch needs to be increased.

I'd say that would be just before cavitation sets in, regardless of which type prop, or type of set-up you use.

Regards, Jan.

Is there a way to predict cavitation speed?

OK I know that it's probably tough to make any certain predictions, but I'm just wondering if say, 30,000rpm is too fast of a speed for a prop to ever spin. I'm trying to pair up the correct KV motor with a hull and I have no idea what approximation to use. For instance, the predicted no-load speed of a motor is 47,000rpm. I'm guessing that under the load, this motor will achieve maybe 30krpm. I'm wondering if this is just too fast or if a transmission needs to be used here.

Thanks

Seems to me that the sweet spot is between 24 and 30k. From there you play with the prop. Id guess that if your NL is 47K that you will be above 30k with a load. The motor will just pull more current as you load it further.

Alright, maybe I should aim for lower KV to put it around 35-40K without load. Thanks for the advice.