Outboard Marine Corporation (OMC) cost figures on Project 443, and early 1980’s project to develop a propeller guard to protect people and minimize performance (top speed and fuel consumption) impacts per some OMC experts sometimes.
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Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC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