RedactedNarrative: Operator stated he was moving at idle speed and left the helm to go aft to relieve himself.  His dog followed him.  He advised that he told the dog to go back to the bow and lay down.  The dog headed back to the bow via the operators seat.  As she made her way forward, she stepped on the throttle throwing the operator over the stern.  The vessel continued on its own in a wide port turn until it struck the pier.  He advised he swam to the location of the collision.