Our To Do List: Propeller Safety projects

Below is a list of the special projects the is working on, in addition to maintaining our existing web site, recording propeller accidents on our Media Coverage of Propeller Accidents Blog, and other elements of our mission.

Many of the projects are already well underway, but we will not complete all them in 2022, some will be carried over and others will be replaced by new projects, but this is our current agenda as of the Summer of 2022.

2022 Projects

  • Working on a four volume manuscript on three early propeller guard reports (the 1989 NBSAC report, the head and leg underwater propeller strike project OMC and Mercury conducted at State University of New York (SUNY) at Buffalo. The project points out previously known problems with this research plus several addition problems we identified by sleuthing through thousands of old documents and reports.
  • Working on a series of about a dozen posters based on the manuscript above.
  • Following up on couple ideas that may reduce the number of those bow riding on pontoon boat struck by the pontoon boat’s propeller. We have technical paper in process on these topics
  • Continuing to promote Post Sale Monitoring of Product Safety such as boat builders using the U.S. Coast Guard Boating Accident Report Database (BARD) to monitor their boats in the field for any potential issues.

In addition we will be maintaining several existing projects including:

  • Continuing to archive and log media reports of boat propeller accidents.
  • Monitoring industry statements about propeller safety issues and make sure those comments are consistent with existing data and events.
  • Closely following the rapidly developing field of virtual propeller guards.
  • Closely following the rapidly developing field of detecting objects in the water (logs, shallow bottom, floating trees, debris, etc) before they are struck by the vessel.
  • Developing lists of similar accidents for various propeller accident scenarios, while updating the lists we have already established from time to time.
  • Keeping alive the “Don’t Wreck Your Summer” Public Service Announcement (PSA). The boating industry effectively banned USCG from airing a high impact video PSA featuring a propeller accident.
  • Promoting the concept of Flip-Up guards for houseboats and pontoon boats. It is a convention cage except the end cover (cap) to the rear flips up when underway due to a tab near the bottom of the flip up portion. The tab creates enough weight to pull the cap down when at rest, and enough resistance to flow when going forward to cause the cap to rise and ride parallel to the surface when underway. The design reduces drag when underway, while still providing full protection to the rear when stopped or in reverse.
  • Promoting the concept of retractable propeller guards. Guards that can be retracted at speed (or automatically retract) to minimize the problems some guards have at speed.
  • Calling attention to the ten thousand plus accidents reported to BARD but invisible to us due to state privacy issues, involving a commercial or state owned vessel, and other reasons.
  • Assisting in reviewing ABYC proposed standard updates
  • Maintaining the ability of our site to be viewed from mobile devices.

Some items always on the back burner for future attention are:

  • Working on a visual representation of how propeller safety devices are selected tied to some work we did in another field.
  • Calling more attention to the possible application of two old Brunswick trim cylinder system patents (U.S. Patent 3,999,502 and U.S. Patent 4,050,359) to cage type propeller guards. The patents describe a method that allows a marine drive to freely swing up and over obstacles when striking them at slow speeds. This is in addition to the pressure relief valves and memory piston system normally used to rise up and over obstacles struck at high speed such as submerged logs. These designs were initiated by Brunswick to help prevent people from being thrown from a boat when striking an obstacle at slow speed (not enough momentum to open the system for high speed strikes so the boat abruptly stopped, or if their was enough momentum there would still be an abrupt jerk as they kicked in).The approach described by the patents may have application to propeller safety in two manners. (1) Reducing blunt trauma to people and marine mammals (like manatees) that might be struck by a guard at slower speeds. (2) Protect guards themselves from damage due to striking rocks, other obstacles, or striking bottom at slow speeds. The drive would just swing up with minimal impact to the guard.The forces on the guard during a slow speed forward impact would be limited to the propeller thrust and the forward momentum of the lower unit of the drive. Those forces would even be somewhat counterbalanced by the momentum of the portion of the drive above where it hinges.Proper sizing of the components might significantly reduce blunt trauma loads to people and impact loads to drives on up into midrange speeds.

    The two Brunswick trim system patents can be viewed by entering their patent numbers 3,999,502 and 4,050,359 one at time into the search box at Google Patents. The interesting part is what they call “trail out” at low speed impact.

    The process is detailed further in our response to withdrawal of the houseboat proposed regulations.

    More recently, Teleflex has been awarded a patent that appears even more promising, and actually a cost reduction.

  • Drawing a huge “Fault Tree” that uses logic “ANDs”, “ORs”, etc. to show how and where various propeller injury avoidance devices try to break the accident chain and which accident chains they can and cannot break, as well as how multiple propeller injury intervention devices and approaches interact with one another.
  • Following up on some propeller flow and wake studies that appear to open up a concept nobody seems to have looked into before. It involves the inflow path to propellers when they are not advancing (when the prop is turning but the boat is not moving, like when the boat is just starting to take off) and concerns the slope of the open surface of the water on the suction side of the propeller.
  • We will be working on a paper on the math on the striking of submerged objects by outboard motors, the forces involved, and how those forces are dissipated, including what happens if the outboard is broken by those forces.
  • Encourage use of two stage tilt cylinders on outboard motors to allow the outboard motor to clean objects struck in the water before the system heavily damps their upward swing.
  • Promoting the use of computer simulation and other tools to study flow, drag, pressures, and interactions around propellers and propeller safety devices.
  • Attempting to better organize our collection of paper documents.
  • Trying to get a better grasp on how people might be better modeled near the propeller in both reality and in simulations (physical objects in the water and computer models) by studying related fields.
  • Increase availability of several older propeller guard / propeller safety videos.
  • Trying to gain full access to non-private info in the U.S. Coast Guard Boating Accident Report Database (BARD).
  • We have been thinking about creating a Propeller Safety Hall of Fame to call attention to those who have or are laboring in this field.


If anyone has any comments, suggestions for areas of study, or would like to help in these efforts, please see our How Can I Help page or contact us.