RedactedNarrative: BOAT OPERATOR STARTED BOAT IN PREPARATION FOR LAUNCH. AN EXPLOSION OCCURED WHICH IGNITED A FIRE. BOAT AND ITS CONTENTS SUSTAINED SEVERE DAMAGE. OCCUPANTS WERE UNINJURED. UNABLE TO DETERMINE WHAT IGNITED THE FUMES DUE To FIRE DAMAGE. Operator did not open any hatches prior to starting, unknown if blowers were operational