ABYC (American Boat and Yacht Council) and CED (CED Investigative Technologies) recently completed a draft of the Propeller Guard Test Protocol. We announced they requested public comment from interested parties by April 11, 2012 on our Propeller Guard Test Protocol Released by ABYC/CED for Public Comment page.
We sent in our comments today (April 11, 2012) and are posting them below. Read More→
CED Propeller Guard Testing @ SUNY
ABYC and CED have completed the rough draft of their propeller guard protocol, titled “The Effectiveness of Propeller Guards” and are now putting it out for public comment before delivering the final draft the the U.S. Coast Guard later this Spring. Read More→
Dr. Lawrence E. "Larry" Thibault
Dr. Thibault, a former Chairman of the School of Bioengineering at the University of Pennsylvania, and founded Biomechanics, Inc. at Exton Pennsylvania. As Biomechanics Inc. he represented many propeller accident victims or their survivors. Read More→
A paper by Thiago Teixeira and Andreas Savvides from Yale and Gershon Dublon of the Massachusetts Institute of Technology surveys methods used to detect the presence of humans. This work could be very useful for those designing virtual propeller guards (propeller guarding technologies based on sensors).
The paper, A Survey of Human-Sensing: Methods for Detecting Presence, Count, Location, Track, and Identity, creates a taxonomy of observable human properties and physical traits (what can be sensed to detect human presence) along with the methods that can be used to detect them.
Their work is a considerable enlargement of the work done by a European college student we helped back in 2005, Human Body Detection Methods: A Literature Review.
The current researchers also discuss the use of sensor fusion (the use of multiple types of sensors in the same system) to reduce false positives and improve overall accuracy. We first encouraged the use of sensor fusion in virtual propeller guards in response to an April 2002 NASA article discussed on our Technologies <2011 page. Brunswick later followed by suggesting the use of multiple sensor types in their infrared virtual propeller guard patents by Staerzl (U.S. Patent 7,476,862 and U.S. Patent 7,511,276). Read More→
Prior to mid 2011 we captured technologies with potential applications to virtual propeller guards (sensor based guards) or to conventional boat propeller guards on our Technologies page, now titled Prop Guard Technologies <2011. With the advent of our new site, we are moving future posts of this nature to their own category which we are launching today (March 25, 2012). Our earlier information on potential Propeller Guard Technologies will remain on the old <2011 page.
Some of these technologies may have application to other guarding applications as well.
Vlist Propeller Safety Project. Eindhoven University of Technology. Netherlands. 2005.
Propeller Guard Design: An Investigation Using CFD. Oliver Lee. University of Sydney (Australia). November 2011.
Mercury Marine CFD mesh
We first heard from Oliver Lee back in late March 2011 as he was getting underway on his Senior Thesis and were able to point him to some information and other studies he found helpful.
Since then he took on a broad swath of propeller guard topics in addition to performing the CFD analysis:
You can download the full pdf document from the link below the thesis. Read More→
Marine drive companies have long employed damping / cushioning technologies to protect marine drives, most typically trim cylinder log strike systems that allow the drive to swing back, up, and over underwater obstacles. Recent years have brought several through hull drives to the market, most prominently Volvo Penta’s IPS, and Brunswick’s / Cummins Mercruiser Diesel (CMD) Zeus Pod Drive.
Cummins MerCruiser Diesel (CMD) Zeus Drive
In November 2011, Brunswick was issued U.S. Patent 8,062,082 for a “Marine Drive With Staged Energy Absorption Capability”. Targeting through hull drives, the patent describes a drive with a long, crushable nose cone. Depending on the amount of energy to be expended when a drive strikes an obstacle (speed of boat and mass of the boat), the nose cone can crush to absorb the energy, or the drive can “breakaway” from the boat. At lower energies (lighter boats and slower speeds) the nose cone crushes to absorb the energy, slow the boat, protect the main part of the drive, and prevent the boat from stopping so fast that people would be ejected. At higher energies (heavier boats and faster speeds), the drive breaks away in a manner that maintains the integrity of the hull and prevents water from entering the boat. The patent includes several charts showing the deceleration capabilities of varies designs. Brunswick introduces the idea of not only crushing the nosecone to absorb the energy, but also of allowing water to fill the nosecone, then forcing it out through one or more orifices during a collision, of filling the cone with an impact absorbing structure, filling the nosecone with an energy absorbing foam, and review previous approaches by others.
The industry is identifying technologies that can protect the boat, and the drive, and do so in a way that does not cause sufficient rapid deceleration to eject people from the boat.
Some of the earlier technologies, and the some of the more recent developments appear to hold significant promise for being able to reduce the impact / blunt trauma felt by humans when struck by a propeller guard. Anything that can reduce the rapid acceleration felt by humans when struck by a marine drive or guard AND the duration of that acceleration is a candidate for reducing injuries and their severity.
We anticipate publishing a post on the science behind blunt trauma injuries in the future which should also be a helpful reference to those pursuing this project. For those not familiar with blunt trauma injuries or who just think of them resulting from being whacked or hit with something, blunt trauma injuries result from sudden accelerations or sudden decelerations. Our organs, tissues, and even bones are damaged when they are accelerated or decelerated too quickly. Blunt trauma injuries can be reduced by reducing the peak accelerations and decelerations of humans struck by propeller guards.
We propose students consider Cushioned Propeller Guard design projects for their Senior Design Projects, Sr. Thesis, and Capstone projects to better protect humans and marine life from being struck by a propeller guard, and provide further information below. Read More→
This propeller guard selection guide is NOT ready for use. As brightly emblazoned on our documents, they are rough drafts. We posted them to generate a discussion that could improve them as well as provide some ideas to those working on the U.S. Coast Guard’s recently announced efforts to produce a consumer guide to propeller guards.
Our guide also covers safety interlocks, changing boater behaviors, boating safety classes and other boat propeller risk reduction activities.
Our Propeller Accident Risk Reduction process is guided by three documents: Risk Proofing My Boat Against Propeller Injuries (describes the overall process), Propeller Risk Worksheet (large checklist that collects information to aid in decision making), and the Propeller Injury Avoidance Device Radar Plot (graphical representation of performance of various devices in different propeller injury scenarios).
Risk Proofing My Boat Against Propeller Injuries lays out the process, defines the terms, and identifies many possible actions that could make your boat less likely to be involved in a propeller accident.
It also teaches about five categories of Propeller Risk Reduction Activities: Read More→
The boating industry continues to reject the use of propeller guards and vehemently testifies against them in propeller injury trials. One of their tools is to illustrate ANY changes in the performance of the boat with the guard vs. without the guard and claim those changes are unacceptable.
We propose a Senior Design Project, Capstone Project, or Senior Thesis in which students develop a propeller guard that provides at least some level of protection while absolutely not changing the performance of the boat and not causing any other unintended consequences. This Senior Design Project might particularly appeal to student in mechanical engineering students, marine engineering, ocean engineering, design, CAD / computer aided design, safety, or law.
In real life, propeller guard designers design guards to maximize protection while minimizing the guard’s impact on the performance of the boat. They typically end up with a prop guard that provides good protection, but one or more element of boat performance is at least measurably impacted (top speed, time to plane, handling, steering, performance in reverse, durability, increased potential area for blunt trauma, entrapment in the guard, fuel consumption, emissions, porpoising, draft, weeds/sea grass, ability to speed to shore after an accident, cavitation, etc.)
Guard designers think it is a very good tradeoff (get great protection but boat goes a couple miles and hour slower, etc.), however the boating industry uses that delta (change in one or more boat performance variable) as a reason to reject the propeller guard. Read More→
Boat propeller guards create drag which effects the performance of the boat, especially the top speed attainable at wide open throttle and time to plane. Propeller guard designers try to minimize drag by increasing the size of the mesh (make the open holes larger) and by decreasing the size of the wires / rods used to construct the mesh. However, those actions begin to reduce protection provided by the propeller guard, its rigidity and its strength. Prop guard designers make these tradeoff without an in depth understanding of all the variables involved.
We propose further research by students as Senior Design Projects, Sr. Thesis, Masters Thesis, and Capstone projects on the drag created by the components (meshes, screens, wire, rods, struts) used to construct propeller guards in clean flows and in the turbulence present in their operating environment. Read More→