5000 to 5500 is the optimum operating range. If the motor is running up to 6000 rpm than the risk greatly increases that it may suffer mechanical failure as that any ventilation of the prop, at this point, will cause undo stress on the rod bolts. Hope this helps.
Thanks for the quick reply. One more question. I pulled the prop off to check it. It has a 12 3/4 inch 21 pitch prop on it and I am running it on a boat rated for a 150 hp max, a fish and ski. Will that prop perform well?
