RedactedNarrative: Vessel 1 was in operation, headed outbound on Rocky River, being run in a troubleshooting test run before being trailered for winter storage.  Vessel 1 was briefly brought up on plane, and as it came back down off plane, the Operator heard a "pop" behind him.  An explosion had occurred in the stern of Vessel 1, blowing open a storage hatch on the port side and blowing the speakers out of their housing.  Following the explosion, the Operator set anchor from the bow of Vessel 1 and put on a PFD. As more smoke started to build, the Operator opted to exit Vessel 1 into the water where he was picked up approximately 30 minutes later by the local fire department.  The fire department also fought the flames now engulfing Vessel 1; following the fire, Vessel 1 remained upright for approximately 45 minutes, then turtled and drifted west where it sank north of Lakewood.
   
  Per investigation by the Ohio State Fire Marshall:
  "The area of origin as the engine area of the boat.  Fire patterns show fire travelling from this area to other systems on the boat.  I was unable to determine a specific area of origin.  Based on my education, training and experience, scene examination and statements obtained; it is my opinion that the case of this fire is UNDETERMINED.  I was unable to eliminate the engine as the heat source for this fire."