I'm new to boating, so any information is probably useful! I have a 89 Bayliner Capri 21' Cuddy with a 3.0. I was on the river when I heard a light vibrating noise. I thought it was no big deal because the night before I put caps on the battery and they weren't too tight. I drove just fine for about 30 minutes and at one point I gunned it and I heard a loud sound. I killed the throttle and slowly brought it back up. The boat was moving very slowly and then eventually, the prop stopped spinning. I checked the prop and the bolt holding it was loose. I tightened it and still nothing. I recently learned (through reading forums) that I should not be spinning the prop when the trim is up, and I have been doing that often because the river gets low. Any suggestions of what it is and what I can do? Thanks.