RedactedNarrative: Owner/operator reported he had purchased the vessel the day before and was taking it out for the first time.  He had just put fuel in it at Mayea Marina/Island Grill and had just made it to the mouth of the Swan Creek and Bouvier Bay when he heard a popping noise. The engine compartment was on fire.  There were two passengers one on each side of the engine that received second degree burns, and one passenger at the stern of the vessel that received 2nd degree burns.  Victim was burned over 40 percent of his body.  The victims jumped into the water and were picked up and taken to shore by a nearby vessel that saw the explosion and fire.  Victim was flown from MacLaren Hospital to University of Michigan Hospital in Ann Arbor for treatment.  Deputy a certified boat accident investigator reported that it appeared to be a possible fuel line or electrical issue that caused the explosion/fire.  He will be going to Michigan Marine Salvage in Harrison Twp where the vessel is being stored for further investigation of what may have happened.  No one was wearing a life jacket.