An outboard motor boat experienced propeller disengagement and damage to the transom area where the motor connected to the boat. An ACS engineer investigated and found fiberglass stress fractures as well as a fracture in the metal mount bolt plate on the port side oriented to the left (away from the keel and stern). Striations and nicks on the propeller blades were also observed. All of the damage was consistent with normal wear and tear for the motor boat’s age and use. The propeller disengagement was due to fatigue.