We examine the propeller guard Rating system and the numbers and data behind those Ratings as defined by the new U.S. Coast Guard (USCG) / American Boat and Yacht Council (ABYC) Propeller Guard Test Procedure.
The new propeller guard test procedure (originally called the Propeller Guard Test Protocol) assigns ratings (typically 0,1,2,3) to prop guards in each of four categories:
The procedure stresses it is for testing guards on a specific or unique boat. Comparisons between different guards will only be valid if they were tested “using an identical boat/engine combination.” Read More→
The boating industry often cites the dangers of being struck by a propeller guard as a reason for not using them. They claim boat propeller guards exhibit a much larger cross sectional area than an unguarded propeller and as a result those in the water are much more likely to be struck by the prop guard than struck by the propeller. The industry also claims blunt trauma injuries from being struck by a propeller guard are more significant than the “clean cuts” resulting from being struck by an open propeller.
Many of us hear or use the term, blunt trauma, without really understanding what it means. We grow up hearing about people being hit by blunt objects and suffering blunt trauma, but just exactly what blunt trauma is remains a bit nebulous.
When the human body is struck by a blunt object that does not penetrate the body, the body must absorb the blow. That energy can be absorbed by:
This post is Part 2. Please view Part 1 first.
Per Biomechanics of Chest and Abdomen Impact. Chapter 53. David Viano and Albert King. Biomedical Engineering Fundamentals:
“The biomechanical response of the body has three components: (1) inertial resistance by acceleration of body masses, (2) elastic resistance by compression of stiff structures and tissues, (3) viscous resistance by rate-dependent properties of tissues.”
At moderate impact speeds, your body just deforms some to accept the impact OR it deforms enough to buy time until the affected segments of your body begin to move to absorb the load.
At higher impact speeds the ability of the body to deform is limited by its inertial and viscous properties. It can’t deform if it can’t get some of the internal fluids and tissues out of the way fast enough. You can be severely injured before your body can get out of the way.
The ability of an organ to absorb impact energy without failing is called tolerance.
Our bodies are well suited to try to protect our most valuable organs. For example: our brain is surrounded by our skull, our heart, lungs, liver, and kidneys are protected by our backbone and ribcage. Our extremities (arms, hands, legs, feet) are less protected, but more expendable. We can still survive if they are crushed (and we quickly receive the level of trauma care available at many major hospitals). One of my uncle’s had his arm crushed between a dump truck bed and its undercarriage a few years ago. Even though he was trapped for several hours before anyone became aware of his predicament, his arm was saved and he has since been been able to recover much of his previous capabilities. If his chest or head been similarly smashed, he would probably no longer be with us.
Vian and King note chest impacts compress the ribcage causing a tensile strain on the outside of the ribs. As compression increases, so does the risk of rib fractures. They also note that blunt impact of our upper abdomen (just below our rib cage) can compress and injure our liver or spleen before our body begins to accelerate from the force.
Common techniques to minimize blunt trauma injuries are to:
We have since had time to quickly read through it and have a few comments:
1. The entire document appears to have been re-written since the October 2012 version. A quick comparison of page 3 of the new version and corresponding portions of pages 2 and 3 of the old version (both versions shown below) make that pretty obvious.
The October 2012 version below talks about the tests being a way consumers could evaluate propeller guarding products, and how manufacturers might include test results on their packaging and advertising materials. They say its purpose was “to evaluate the essential safety consequences of installing a propeller guard on an outboard or sterndrive boat. Read More→
The two major U.S. recreational marine drive companies of the past many years: Brunswick / Mercury Marine and Outboard Marine Corporation (OMC) have been in the forefront of “debunking” propeller guards in court since the 1970’s. In this post we estimate their total expenses in developing propeller guards designed to protect people at less than $25,000 combined.
Outboard Marine Corporation was formed in 1929 from the merger of two existing outboard motor manufacturers. OMC went bankrupt in December 2000, but their insurance company still represents them against propeller injury claims.
Mercury Marine began as Kiekhaefer Corporation in 1939, and was acquired by Brunswick Corporation in 1961.
During the late 1980’s and in the 1990’s OMC and Mercury often worked together in testing propeller guards, most notably during the November-December 1990 SUNY tests. They also collaborated on legal defense efforts. Dick Snyder, Mercury Marine’s expert witness in propeller injury cases, served as an expert for OMC in several cases as well. Plus they conducted a large joint mock propeller trial in early 1989. Mercury later tried to downplay this period of legal cooperation with OMC against their common enemy (propeller injury suits). We mention this period of cooperation because it is relevant to Mercury and OMC being the major industry voices in the U.S. against propeller guards.
We (and they) have occasionally been asked how much money they spent trying to develop a “people protecting” propeller guard. The “people protecting” part is important as the industry has developed a few propeller guards which they claim were not for protecting people or were for protecting people in an extremely limited instance. Quite recently we were asked this same question again so we began to gather documents and created this post. Read More→
The petition itself is very brief and to the point, “Put cages on boat propellers.” It can be signed on Change.org. Over 630 people have already signed the petition. The petition is accompanied by a photo of a leg struck by a boat propeller.
Please sign their petition, and help Cian continue to draw attention to the dangers of exposed propellers.
Three recent events are cited as examples:
Royal Yachting Association (RYA) recently updated their position statement on the use of propeller guards. The well known national UK boating association replaced their 6 May 2009 one page statement, Guidance on Prop Guards, with:
We had heard RYA was going to be softening its stance a bit, plus we were aware they had been involved in conversations about the 20 July 2012 Charlie Hutton fatality.
While the new documents may be slightly “softer” they do not reflect the considerably softer stance we had anticipated. Read More→
Madi Abeid published, “Boat Propeller Guards: A Smart Choice” in a March 18, 2013 special issue of the Cape Cod Times. She was drawn to the topic after her sister was struck by a boat propeller in July 2012.
Madi notes that if a guard had been installed her sister would not have spent most of the summer in the hospital, that boating injuries occur more frequently than most people think, that marine life can also be struck by propellers, and she iterates the objections raised to propeller guards. Madi concludes with, as responsible boat owners consider the arguments from both sides, she thinks they will seriously consider using propeller guards.
She presents an excellent synopsis of the situation, but the most remarkable point is left out. Madi Abeid is a seventh-grader at Nauset Regional Middle School in Orleans near Cape Cod, Massachusetts. This young girl who may not even be a teenager yet, has an excellent grasp on the issues the industry and propeller safety advocates have been debating for decades. Read More→