On May 21, 1997, about 0930 Alaska daylight time, a tundra tire equipped Cessna 180, N24EJ, ditched in the ocean about 10 miles west of Shaktoolik, Alaska. The airplane was being operated as a visual flight rules (VFR) local area business flight under Title 14 CFR Part 91 when the accident occurred. The airplane, registered to and operated by the pilot, sustained substantial damage. The certificated commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. The flight originated at the Shaktoolik airport, about 0910. On May 27, 1997, at 1018, the pilot reported in a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), that he was conducting fish spotting flights in the Cape Denbigh, Alaska, area. While spotting fish, the pilot was circling to the left. He was about 600 feet above the water when the engine coughed several times and then quit. The pilot switched fuel tanks several times but the engine did not restart. He performed a landing into the water about 50 yards from the beach. After touchdown, the airplane nosed over. The pilot indicated he last fueled the airplane before departure from Unalakleet, Alaska, about 0500 but had landed twice at Shaktoolik during the morning flights. The pilot reported the airplane contained about 22 gallons of fuel when he departed on the accident flight. The left fuel tank was indicating 1/3 and the right tank was near empty. The pilot estimated he still had 1 and 1/2 hours of fuel on board, and operated the airplane fuel selector in the "BOTH" position. The airplane's engine had accrued about 30 hours since being overhauled. The pilot reported the weather conditions in the area were scattered cloud conditions at 600 feet, 1,000 feet broken. The temperature was about 35 degrees F. Numerous rain showers were moving through the area. The visibility was about 20 miles. The wind was from the southwest about 15 knots with gust to 20 knots. The airplane's fuel system consists of two rubberized bladder fuel cells, one in each wing. Fuel flows by gravity through a fuel selector, fuel strainer, and then to the carburetor. The engine does not have a mechanical or electrical fuel pump. Following the accident, the pilot sold the airplane to a new owner. The new owner recovered the airplane from the ocean, and reported the fuel selector was found in the "BOTH" position. The carburetor heat control was in the "ON" position. The throttle, mixture, and propeller controls were full forward. About 15 gallons of fuel was drained from the left fuel tank, and about 5 gallons was drained from the right tank. Fuel was found in the gascolator, carburetor bowl, and carburetor accelerator pump. On June 4, 1997, the engine was examined at John/Mark Air Repair, Birchwood, Alaska. Gear and valve train continuity was established upon hand rotation of the engine crankshaft. The oil screen was free of contaminants. The oil pump housing, and internal gears were free of contaminants, and rotated. The magnetos had been removed from the engine, and upon hand rotation, both produced spark from all towers. The carburetor's fuel inlet screen exhibited slight evidence of corrosion, but was free of contaminants. The carburetor metal floats were undamaged. Examination of the interior of the carburetor airbox, and venturi, revealed a blackened appearance, and evidence of slight sooting.