Cliff, I've got a rather spendy stainless prop on my motor.
Two years ago when I was heading to Lakair, the water was down about 4' and rather than taking a chance on smashing it on a rock, I went to the local marina and bought a regular rather in-expensive prop that was sposed to work on my motor.
Same as your friend, as soon as I'd hit around 2500 RPM's the prop would just spin on the hub and the engine would rev high.
No other choice but to take it off and put the good one on and just keep my fingers crossed.