Brunswick Corporation’s Starter Interlock, U.S. Patent 4,064,823. This safety feature is to prevent outboard motors from starting in neutral.
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Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC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