Several boat accidents of outboard motors striking submerged objects, often a submerged log and flipping into the boat. Some may have slipped off outboard jackplates.
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Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC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