On May 23, 2016, about 1137 Hawaiian standard time, A Beech C23, N6697Y, sustained substantial damage following a loss of engine power and subsequent ditching within the open waters of the Pacific Ocean near Waianae, Hawaii. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The private pilot and his passenger sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight. The cross-country flight originated from the Lihue Airport, Lihue, Hawaii, about 20 minutes prior to the accident, with an intended destination of Kalaeloa Airport, Kapolei, Hawaii.The pilot reported that during the climb to cruise portion of the flight, the engine began to run rough. The pilot applied carburetor heat, which resolved the roughness, and he continued his climb to 5,500 feet mean sea level. As the flight was approaching the shores of Oahu Island, the engine began running rough in addition to a reduction of engine rpm to about 1,700. The pilot applied carburetor heat and adjusted the mixture, however, was unsuccessful at restoring engine power. The pilot initiated a forced landing into the ocean waters just off shore of the island of Oahu. The airplane came to rest nose low partially submerged within about 20 feet of water, about 50 to 75 feet from the shoreline. Initial examination of the wreckage revealed that the forward portion of the fuselage was damaged. The wreckage was recovered from the water three days after the accident. Following removal from the water, the engine was rinsed with fresh water and subsequently filled with diesel fuel in an attempt to preserve the engine. Examination of the recovered airplane on June 30, 2016, revealed that it was mostly fragmented into multiple pieces from the ocean tidal action. The engine remained attached to the firewall structure. Corrosion was observed throughout the engine and firewall. The carburetor was separated from its mounts. The magnetos and fuel pump remained secured to their mounting pads. The bottom spark plugs were removed and exhibited corrosion and debris consistent with ocean water and salt. The magnetos were removed. Partial rotational continuity was obtained when the propeller was rotated about ¼ of a turn and mechanical continuity was obtained at the rear of the engine. The right magneto drive shaft rotated however did not produce spark at the lead terminals. Disassembly of the magneto was not performed due to the corrosion on the cap bolts. The left magneto drive shaft would not rotate by hand. Disassembly of the magneto was not performed due to the corrosion on the cap bolts. The carburetor was removed and disassembled for inspection. The internal float was intact and the needle valve was intact. A significant amount of salt and other ocean vegetation debris was observed throughout the float bowl and screen. The right side exhaust remained partially attached to cylinders one and three. No nuts were observed on the cylinder number one exhaust mount and only one nut remained attached to the cylinder number three cylinder exhaust mount. It could not be determined if the missing nuts were displaced prior to the accident or during salvage and subsequent engine preservation methods. No evidence of any preexisting anomalies that would have precluded normal operation and production of power was observed. The Federal Aviation Administration (FAA) published Special Airworthiness Information Bulletin (SAIB) CE-09-35 on June 30, 2009, regarding carburetor ice prevention. The conditions encountered in this accident (ambient temperature 84 degrees F, dew point 63 degrees F) were in the area of icing at glide and cruise power, and in the area of serious icing at glide power.