RedactedNarrative: Vessel #1 had completed refueling and the vessel operator stated he turned on the blower for approximately seven minutes.  Vessel #1 operator attempted to start the motors an when he did a large explosion occurred in the engine compartment.  The explosion blew off the the engine cover with no post explosion fire.  A.O.I was at the Pier 51 refueling dock and .1 mile south of Pier 51 Boat Ramp.  One of Pier 51 maintenance technician and Vessel #1 operator's father discovered a fuel line to the generator had been disconnected.  Earlier that day Vessel #1 operator changed the battery in the vessel and possible stepped on the fuel causing the fuel leak in the engine compartment.