A few cyclists during a break of the Milligan Charitable Ride in the UK 20-22 June 2014. Image by Adrian Floyd of Finton House. We borrowed it via his twitter post.
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Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC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