RedactedNarrative: OPERATOR STATED HE RECENTLY HAD WORK DONE ON V1. HE FURTHER STATED HE RENTED A BOAT SLIP FOR THE NIGHT AND UPON DOCKING FILLED V1 WITH FUEL.  HE CONFIRMED AT NO TIME DID HE ENGAGE THE BLOWER; IN FACT HE JUST PURCHASED V1 AND DIDN'T EVEN KNOW WHAT THE BLOWER WAS USED FOR.  THE NEXT DAY V1 OCCUPANTS HEADED OUT TOWARD THE HWY 12 BRIDGE AND REPORTED HEARING A LOUD BANG AT THE STERN OF V1 AND THEN SMOKE COMING OUT FROM THE ENGINE COMPARTMENT. UPON LIFTING THE ENGINE COMPARTMENT COVER FIRE ERUPTED AND ALL OCCUPANTS JUMPED INTO THE WATER AND SWAM TO SHORE.  UPON INTERVIEW V1 OPERATOR ALSO STATED HE LEFT A 12V AIR PUMP IN THE STERN COMPARTMENT (LOOSE); HE STATED THE CLAMPS COULD HAVE BOUNCED AROUND AND CAUSED A SPARK.