Funny sound

In the files of weird stuff that happens to boats is this little story.

At the end of last season there was a funny sound coming from the back of my boat (89 Sunsport). It was in the area of the transmission, but seemed underneath the boat. The sound was mostly absent in reverse and increased with RPMs. We boat on a fairly shallow river and usually leave the boat in the water until it's time to winterize. This started as we pulled into the marina on our last day last November. We parked the boat in the slip and the sound was still there when we came back to get the boat out. Once we pulled it out of the water the problem was clear. Somehow a 12" nail had been picked up by the prop and wrapped around the drive shaft. The channel is quite shallow coming into the marina (soft mud though). The prop must have hit the nail with the right angle so it bend around the drive shaft. In reverse, it was pulled up the drive shaft and stopped spinning and hitting the bottom of the boat. In forward, it was caught in the prop and slapping the boat with each revolution. Fiberglass looks ok though. So hopefully everything is right when we get back in the water.Attachment 17011

Wow that's a crazy coincidence to hit it just right. The gel coat alright too?

That's about what a 12" nail would look like if I tried to hammer it into anything. What the heck was that thing used for?!

Gel coat looks a bit scuffed, but not bad.
No idea what it was used for. The end wasn't sharp and it's not thick enough to hammer on. The marina had recently put in a new dock, but it's hard to imagine it was part of that.
Rivers can carry some odd things.