On July 10, 1999, about 1330 eastern standard time, a Ryan ST3KR, N47306, registered to an individual, received substantial damage during cruise flight, and made a forced landing at the Lake City Airport, Lake City, Florida. The airline transport-rated pilot reported no injuries. Visual meteorological conditions (VMC) prevailed in the vicinity, and no flight plan had been filed. The personal flight was being conducted in accordance with Title 14 CFR Part 91. The flight had originated at Albany, Georgia, at 1300. At a cruise altitude of 2,500 feet msl, and about 7 to 8 miles north of Lake City, the pilot reported that the airplane started to vibrate. He attempted to shut down the engine with no response. The only response he could get was to the throttle. He elected to land at Lake City, and landed without incident. Examination of the airplane revealed that the propeller came loose from the flange. All of the propeller bolts were found backed out, and none of the bolts were safety wired. The pilot had just purchased the airplane. According to the FAA inspector's statement, when he examined the airplane after the accident he observed, "...several inches of the leading edge of one blade of the propeller missing...broken across [the] grain and glue lines." The inspector found the propeller loose in the hub, the bolt heads and holes in the hub were, "...very worn like it has been loose for a while with power." There were no logbook entries found to indicate that the propeller bolts were torqued or tracked on installation or at annual inspection. The FAA inspector stated the following findings, "...one of 2 propeller blades split in half from the center to the tip...the propeller bolts for [the] propeller were found loose at the hub, [and] all evenly backed out approximately one quarter inch...no locking device or safety wire were attached to the bolt heads." The data sheet does not list the propeller for installation on this aircraft.