I local fisherman I know told me something that he said very few people know. I'm not gullible enough to believe this but he said, if you take a brand new prop and very lightly file the edges that it will get you a couple more miles per hour speed. He commented that the props that have a distinctively sharp edge has a tendency to cause a slight cavitation at higher speeds because of the sharp edge. This condition is not necessarily true with all props. It almost sound plausible but I think I'll leave the prop on my new boat alone.
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They will cut grass better with a sharp edge.
I've learned from my discussions with one of the best prop guys in the business, that most new props are not well balanced and are far from perfect out of the box.
A prop shop will sharpen blades upon request and it does improve performance, the prop should be balanced at the same time though. If you have the best prop for your setup and want the absolute best performance, have the prop balanced and blueprinted. The prop shop can make the prop perfect and you will get every MPH possible.
I've had most of my props on my Stratos worked. Had my favorite prop balanced and blueprinted by Mark Croxton. He advised me that he wouldn't put a razor sharp edge on the prop unless I really wanted it. A sharp blade can be nicked easier, nicks in the blades causes cavitation and as a result slippage. So while the blades are perfectly sharp it's great, but every little piece of debris in the water is going to nick it up so the added performance doesn't last long.
Unless it's an alloy or aluminum prop. In that case, don't bother.