Boat has been running strong this year. In the water yesterday for about an hour, stopped to troll for a while. When powering back up to get on plane it goes nowhere. I reduced power to idle and tried again, moved slowly. Tried again after 30 seconds or so and gently got it back up on plane. Ran fine for remainder of the trip, about an hour. My prop is 9 years old, Solas, no issues until now. No burning rubber odor or residue in the engine bay that a failed coupler might give. I ordered a new prop. From other posts on the forum, if a coupler fails you are going nowhere and will overheat the engine since the pump impeller isn't spinning. I'm tempted to pull the outdrive and check the coupler splines to be sure. I haven't checked alignment for a couple of years so it's time for that too. Fingers crossed it spun a prop hub. Would debris in the water cause this to happen? Many many years ago I had a 120 Merc I/O. Coming back to the dock on a beautiful evening and the drive kicks into the air and boat comes to a stop. There was a 6 foot Christmas tree lodged between the drive and bell housing. I had to jump into the water and pry it out. Didn't see that one coming.....