RedactedNarrative: Operator advised that he had boarded the vessel, opened hatches and turned the blower on. After all the passengers had boarded the vessel, the operator started the engine and reversed away from the dock. The vessel exploded when the operator put the vessel in forward gear. Four of the five POB were injured. The vessel was a total loss.  The eplosion was caused by a fuel vapor buildup within the motor box and bilge area. The ignition of the fuel air mixture was from the combustion of the running engine. I believe the extensive damage from the mid line to the bow contributed to the direction and wind speed at the time of the incident. The cause of the explosion/fire is considered accidental in nature.
  The investigator does not provide any details regarding the amount of time the blower had been running prior to the explosion or suggest that additional time would have prevented the explosion.