Outboard motor and stern drive boat trim cylinders are designed to absorb energy during log strikes and the striking of other submerged obstacles or debris.
Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC
History of Boat Propeller Safety
Mitigating Boat Propeller Injuries & Fatalities Chart
Four Volume Review of the Boating Industry’s Boat Propeller Guard Product Liability Defense