Mercury Marine outboard motor tether assembly for a Mercury 1150 (115 horsepower outboard). The metal part is bolted to the swivel bracket and a rod on the transom mount passes through where the yellow stick is. Other side view.
Aspects of the Propeller Safety Debate chart
Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC
History of Boat Propeller Safety
Mitigating Boat Propeller Injuries & Fatalities Chart