RedactedNarrative: Vessel 1 was cruising back and forth on lake mcalester.  Operator said he heard a pop and then noticed flames coming from the inboard/outboard containment area.  Fire then spread and covered the rear of the vessel.  Operator stated he had the ventilation blower on but apparently it did not work.  Passenger attempted to use fire extinguisher to put out the fire but the extinguisher was inoperable.  Occupants then evacuated the vessel and began swimming to shore.  Vessel continued to burn and drifted to the northeast corner of the lake. Vessel broke apart and sunk while attempting recovery.  Area of the accident was approx 350 ft south of the north shoreline and approx 565 feet west of the east shoreline and approx 6.5 miles nw of mcalester.