Prop or gear issue?

I have a 1985 (maybe 86) 25 hp evinrude on a 16' flat bottom. I recently had the boat out and ran into a sandbar going a little over idle speed. I held the motor up to keep prop out of the sand until water was deep again. Began to accelerate to full throttle and engine would over rev like the prop is cavitating. I slowed down, checked for weeds, debris etc... Prop is clean. I assumed spun hub on prop. I changed to a spare prop, same thing happened. Could both hubs be spun? Possible but unlikely. What else could cause this?

 

If you didn't hear any crunching and the linkage is working ie: prop spins under no load at idle, then both props likely are spun

 

How was the spare prop performing before you took it off? They are relatively easy to check. Hold the prop in a vise or something else, and try to turn the hub. If it is spun you will be able to twist it.

 

I'd have thought the 25hp of that vintage might have had a shear pin, certainly a few years earlier did. The 30 and 35 of the era had a similar powerhead, but hubbed props.