On July 24, 1993, at about 0825 eastern daylight time, a Cessna 152, N6091M, registered to Phoenix East Aviation, Inc., experienced a drop in engine rpm while in cruise flight. The private pilot conducted a forced landing to the water adjacent to St. Augustine Beach. On touchdown the airplane nosed over and came to rest inverted. The pilot and passenger were not injured. The airplane sustained substantial damage. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from Daytona Beach, Florida, about 25 minutes before the accident. The pilot stated he was in cruise flight at about 2000 feet agl when he experienced a decrease in engine rpm. The pilot notified Daytona Beach Approach Control of the situation and initiated the emergency procedures in the aircraft checklist. The carburetor heat was turned on, and an increase in engine rpm was noticed followed by a decrease in engine rpm. A forced landing was made to the ocean adjacent to the beach. Examination of the engine assembly and accessories by an airframe and powerplant mechanic with inspection authority revealed no evidence of a precrash failure or malfunction. No determination could be made for the reported partial loss of engine power.