On March 1, 2008, at 1515 eastern standard time, a Diamond DA 20, N859MS, was presumed to be substantially damaged during a ditching in the Atlantic Ocean, near Key West, Florida. The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which originated at the Florida Keys Marathon Airport (MTH), Marathon, Florida, at 1500. The personal flight was destined for the Key West International Airport (EYW), Key West, Florida, and was conducted under the provisions of 14 Code of Federal Regulations Part 91. According to the pilot, after departure he climbed the airplane to an altitude of 8,000 feet and practiced steep turns. He then flew toward EYW, where he intended to practice touch-and-go landings. The pilot reduced the power to idle, and initiated a descent. When the airplane reached the traffic pattern altitude of 850 feet, the pilot leveled-off the airplane. He advanced the throttle to increase the power; however, the engine did not respond. The propeller continued to turn momentarily and then stopped completely. The pilot completed the emergency checklist; however, he could not restart the engine. He reported a "mayday" to air traffic control and gave his position, which was approximately 6 miles south of the Big Pine Key shoreline. The pilot performed a forced landing to the water, and after the airplane came to rest, the pilot opened the canopy and inflated the life raft he had in the airplane. He entered the life raft and watched the airplane float for approximately 5 minutes, before sinking. Approximately 90 minutes later, a fisherman picked up the pilot and brought him to shore. The pilot purchased the airplane new in April 2006. He reported the airplane and engine logbooks were in the airplane at the time of the accident. The next annual inspection was due in May 2008, and no recent maintenance had been performed on the airplane. The pilot reported he last flown the airplane approximately 2 to 3 weeks prior to the accident. He estimated the airplane had "just under full fuel," (approximately 20 gallons), prior to departure. According to fuel records provided by the Fixed Base Operator (FBO) where the airplane was based, the airplane was last refueled on February 6, 2008, with 13.8 gallons of fuel. As of the date of this report, there were no plans to recover the airplane from the Atlantic Ocean.