L/Cpl responded to a boat fire call. She arrived on scene and met with the owner operator of unit 1, the fire department and Sgt. . Per Operator's statement he backed  unit 1 into the water started the motor and turned the bilge on for 5 minute.  Operator then backed unit 1 off of the trailer, turned it around and tied it off to the dock. Operator then heard an explosion in the engine compartment (i/o motor) saw smoke and fire immediately turned the motor and both bilge switches off and extinguished the 2 fire using  fire extinguishers that he had on board. he then turned the batteries off and dialed 911 per the fire departments incident report the cause of the fire is unknown. There was damage to the engine, its compartment and the areas around it that appears to be caused by the fire.