RedactedNarrative: VESSEL ONE WAS BACKING WHEN IT CHANGED DIRECTION TO GO FORWARD TO AVOID COLLIDING WITH A VESSEL BEHIND VESSIEL IT.  THE OPERATOR OF VESSEL ONE OVER THROTTLED CAUSING THE PORT SIDE SPONSON TO COLLIDE WITH THE PORT SIDE STERN OF VESSEL TWO.  VESSEL TWO WAS STILL ON THE TRAILER AND HOOKED UP AT THE TIME OF THE COLLISION.  THE UNKNOWN VESSEL BEHIND VESSEL ONE PRIOR TO THE COLLISION WAS NOT STRUCK AND LEFT THE AREA.