RedactedNarrative: Vessel 1, a rental deck boat that was a twin catamaran style fiberglass hull, was motoring slowly when operator 1 noticed that the boat was not floating normally.  He noticed the bow port side dipping lower.  
  
  When checking the transom area, operator noticed that the hatch cover on the aft port side was missing.  Operator 1 and his son were in wet suits.  The 2 female passengers put on PFD's as the boat began to list to the starboard side.  
  
  Operator motored to an an anchored party fishing boat at which time his vessel rolled over to the starboard side.  All occupants of vessel 1 swam to the Good Samaritan fishing boat where they boarded and were brought back to shore.  Vessel 1 drifted almost due north for 1/4 mile before totally submerging.  It has not been recovered.  
  
  It appears the piano hinged aft starboard hatch, that was held in place by gravity and friction, allowed water to enter in the rough seas.  As the starboard hull filled with water the air was forced in to the port hull that most likely popped the aft port access plate causing the vessel to roll over.