RedactedNarrative: UNIT 1 WAS TRAVELING UP RIVER ON THE ASHLEY RIVER.  UNIT 1 STRUCK A SUBMERGED OBJECT WITH ITS PONTOON.  THE ENDCAP ON THE PONTOON WAS RIPPED OFF CUASING THE TOON TO FILL WITH WATER.  THE VESSEL BECAME PARTIALLY SUBMERGED BUT THE OPERATOR WAS ABLE TO GET IT BACK TO THE LANDING BEFORE THE ENGINE QUIT.