On December 11, 2016, about 1300 eastern standard time, a Beech A36, N69286, was substantially damaged following a total loss of engine power during cruise flight and subsequent ditching in the Long Island Sound, near Shoreham, New York. The private pilot and a passenger were not injured. The airplane departed from Long Island Mac Arthur Airport (ISP), New York, New York and was destined for Westfield-Barnes Regional Airport (BAF), Westfield, Massachusetts. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight conducted under the provisions of 14 Code of Federal Regulations Part 91.According to the pilot, after reaching a cruise altitude of 5,500 feet, the engine started running rough. The pilot then pushed the mixture, propeller, and throttle controls to the full forward position. The engine was still running rough and getting worse. The pilot then decided to turn around and return to ISP. During the turn back to the airport, the pilot noticed oil was covering the windscreen. He then declared an emergency and asked air traffic control for radar vectors to Igor I Sikorsky Memorial Airport (BDR) Bridgeport, Connecticut. The air traffic controller told him to turn north to a heading of 360°, however, the pilot was having trouble keeping the airplane's wings level and did not want to turn that far to the north. The pilot then requested vectors to Calverton Executive Airpark (3C8), Calverton, New York. The controller told the pilot that 3C8 was 7 miles ahead of his current position. At that time, the engine was still producing partial power and the pilot believed he could reach the airport. A few seconds later, he saw parts which he thought were from the propeller, separate from the airplane. The engine then lost total power and the pilot told the controller they would not make the airport and were going to ditch the airplane in the Long Island Sound. The pilot remembered that the airspeed indicator read 80 knots just before contact with the water. Once they ditched in the water, the pilot and passenger opened the door, egressed and swam to a rock that was close by and waited for rescue personnel to arrive. Examination of the wreckage by a Federal Aviation Administration inspector revealed that the right-wing spar was damaged and the engine had several holes in the crankcase. A front section of the crankshaft was fractured and the propeller was not recovered. The engine was sent to the manufacturer's facility for teardown and examination. The teardown revealed that the #4 main bearing journal and the fracture surfaces displayed crack arrest and beach marks consistent with fatigue cracking. The crankcase mating surfaces also revealed signs of fretting at the #1, #2, #3 and #4 main bearing journal case halves. The surface of the #4 bearing journal was obliterated and the #3 main bearing journal showed signs of lock slot elongation. All six connecting rods displayed signatures of lubrication distress. Significant amounts of metal consistent with bearing material and crankcase debris were recovered from the oil sump and observed on the oil pickup tube screen. The through bolt breakaway torque values observed during the disassembly exam were low. The crankshaft was forwarded to the NTSB Material Laboratory in Washington D.C. for examination. A bench binocular microscope examination of the fracture face revealed crack arrest marks typical of fatigue cracking. Scanning electron microscope examination of the fracture face revealed the origin of the fatigue crack contained mechanical damage from relative movement between the mating fracture faces that obliterated the fine fatigue crack origin features. According to FAA and aircraft maintenance records, the airplane was originally issued an airworthiness certificate on February 18, 1984, and registered to the owner on October 9, 2014. It was powered by a Continental IO-550-B1A engine. According to maintenance records, the most recent annual inspection was conducted on June 10, 2016, with a recorded time in service of 1,648.3 hours. The engine had 6 new cylinders installed on May 21, 2012, and had accumulated 163.8 hours of service at the time of inspection.