RedactedNarrative: While cruising operator heard a nose like a thump followed by a vibration.  Upon stopping and checking the engine compartment and noticed the port drive shaft was missing.  The missing shaft and drive left an approximate 6" hole in the transom below the water line causing the vessel to rapidly take on water.  Vessel started sinking.  Occupants had been picked up by a passing vessel who noticed the vessel was very low in the water and the occupants were signaling for help.  The vessel sank.  Total loss.  No injuries.