UNIT 1 WAS CRUISING UP THE WANDO RIVER WHEN THE VESSEL STRUCK THE #3 BUOY ON THE VESSELS PORT SIDE EJECTING ALL FOUR OCCUPANTS INTO THE WATER. THE VESSEL CONTINUED UNTIL GROUNDING ON DANIEL ISLAND APPROXIMATELY 2130 (OP)SWAM TO THE VESSEL IN ORDER TO CONTACT USCG VIA VHF WHILE SWIMMING ASHORE operator RECEIVED OYSTER CUTS ON FOOT AND THE OTHER PASSENGERS CLIMBED ON THE 3RD CHANNEL MARKER UNTIL THE USCG ARRIVED.