On December 20, 1996, about 1430 Pacific standard time, N233C, a Stinson 108-2 airplane, operated by Yelm Aviation, McKenna, Washington, ditched about 2 miles from Friday Harbor, Washington, and is presumed destroyed. The ditching was preceded by a loss of engine power during climb. The airline transport pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The business flight departed from Friday Harbor, Washington, about 1425 and was destined for Yelm, Washington. The flight was conducted under 14 CFR 91. The pilot stated that he had fueled the airplane at Friday Harbor for the flight back to Yelm after a business meeting. The previous flight from Yelm was uneventful. The pilot stated that the preflight inspection, engine start-up, engine run-up, and takeoff were "smooth." While climbing over the Puget Sound through 2,500 feet above mean sea level, the engine "began to vibrate severely with a metallic banging sound." The pilot stated that the noise and vibration lasted about 10 seconds, after which the engine went silent and the propeller windmilled. After all attempts to restart the engine had failed, the pilot ditched the airplane next to a fishing trawler. The airplane nosed over at impact with the water and sank to a depth of about 300 feet after the pilot safely egressed. According to the pilot, the engine, a Franklin model 6A4-165-B3, received an annual inspection by the pilot during the past year with no unresolved discrepancies noted. The aircraft and its maintenance log books where not recovered from the waters of the Puget Sound, and no determination was able to be made as to the reason for the loss of power.