RedactedNarrative: On 6/4/2017 in the morning, Operator & injured were fixing the 2000 cabin motorboat which had been left for months. This would have been the first time out on the water & they fixed the gas line/fuel system. At approximately 3:30 pm when they had the boat first into the water, it died when they pulled up to the beach area.  They let it cool for about 45 minutes and just hung out at the beach. They started back toward the dock since passenger was late for work and were traveling about 10-15 mph.  Both were sitting in the back seat near the engine compartment when an explosion erupted in that area. All 4 individuals jumped out of the boat and into the water.  Several boats saw the explosion and came to rescue the four individuals.  At first they tried putting out the fire with lake water & then realized it was a gasoline fire.  Several boats then used their fire extinguishers to put out the fire.  When contained it was towed to the dock for Fire & rescue to finish securing the boat.  No individuals were wearing life jackets and they were consuming alcohol.