RedactedNarrative: Based on my investigation it is determined that operator was leaving lake st beach and traveling east at a high rate of speed. For an unknown reason operator was ejected from his boat to the port side, damaging the windshield on that side. Operator was not wearing his boat's safety lanyard, so the engine remained running. The motorboat then circled back around without an operator, and struck operator. Operator was struck by the propeller which almost completely severed his right arm, cut open his chest and abdomen, and severed his spine. The motorboat then continued to move in tight circles at a high rate of speed. This stress from circling caused the u-joints to break, puncturing the bellows/boot. Once the u-joint broke the engine no longer provided power to the propeller so the boat came to rest with the engine still on at high rpms. Once the boat stopped, it began to take on water and eventually sank.