I started my 2006 Mercury Optimax 115 engine on my Nitro 189 sport after being anchored for 20 minutes. Moved slowly forward at 900 rpm, Tapped the top of a unknown rock. The alarmed sounded and the engine turned off. Raised the engine and inspected the prop area. NO damage. Tried to start again and alarm sounded and it wouldn't try to turn over. Limped to dock with trolling motor. Pulled boat out. No visible damage. Have not attempted another start. Kind of wish there was a shear pin. Any ideas? Am I in the right forum?