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Boat Propeller Guard Product Liability Defense Intro Vol1

In the mid to late 1980’s Mercury Marine, a Brunswick Corporation, and Outboard Marine Corporation (OMC) were facing a large number of boat propeller guard product liability / product defect lawsuits. Several of those lawsuits related to kill switches not being installed.

This post is the second of a series of five posts announcing the materials we prepared on 3 studies performed by the boating industry. These 3 studies are currently used as their legal defense against boat propeller guard product liability / product defect cases.

This post is a brief introduction to a large four volume pdf report titled Mercury Marine & Outboard Marine Corp. Propeller Guard Case Legal Defense that can be found at Boat Propeller Guard Product Liability Defense.


Volume I: The Introduction post

U.S. Coast Guard emblem

USCG Purcell & Lincoln Boat Propeller Guard Study

The U.S. Coast Guard published their own, in house, propeller guard study by Edward S. Purcell and Walter B. Lincoln in 1987.

The study was conducted by reviewing the existing literature on boat propeller guards.

Purcell and Lincoln’s study was viewed as inconclusive by the Coast Guard in part because Purcell and Lincoln reported:

  1. They needed accurate propeller strike data
  2. Biomechanical testing would need to be performed
  3. Mechanical studies would need to be conducted
  4. Test for severity would need to be conducted
  5. Potential solutions would need to be ranked
  6. Acceptable solutions would need to be identified
  7. Validation testing would need to be performed

The Efficacy / Effectiveness of Boat Propeller Guards

From 1988 thru 1990 Mercury Marine and Outboard Marine Corporation (OMC), were involved in three propeller guard studies.

Once completed those studies were quickly used in court to defend the boating industry’s position against the use of boat propeller guards / prop guards.

Individuals involved in those studies were used as expert witnesses. They explained the results / recommendations of the studies and how they were derived.

Each of the three studies: the 1989 NBSAC study, the SUNY underwater head impact study, and the SUNY underwater leg impact study are briefly critiqued below.


The U.S. Coast Guard 1989 National Boating Safety Advisory Council Propeller Guard Subcommittee Report

In 1988 U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) formed a subcommittee to study boat propeller guards.

Mercury Marine and Outboard Marine Corporation (OMC) both had representatives on this subcommittee. It was composed of 4 to 7 members of the 21 members of NBSAC. Mercury was represented by their corporate lawyer, Roy Montgomery.

NBSAC’s subcommittee report noted, “Several lawsuits involving tens of millions of dollars have been brought to court in the past two years and have heightened interest in this subject substantially.”

The NBSAC study consisted of a review of the existing literature plus presentations by interested parties.

The study said blunt trauma from impacting a propeller guard at speed was worse than impacting an open propeller. (no proof was provided, see discussion in head impact study section below)

Pages 4 and 5 of the NBSAC study lists three legal theories advanced by propeller guard advocates. Pages 5 and 6 along with pages 20 through 22 rebut the use of propeller guards.


Findings of the 1989 NBSAC Report

The NBSAC report states, “Presentations illustrated that approximately 80 percent of all accidents occur when a boat is operating at speeds in excess of 10 miles per hour.” This is one of several examples of the subcommittee taking statements made by the industry as being factual. (see pie chart on our Chart #9 which shows this statement is not be true). A variant of this comment is repeated on page 17 as, “It was repeatedly stated that a skull impact of 10 mph or more in the water would generally be fatal.” Just because a statement was presented or repeatedly stated by the industry, does not make it true.

In November 1989, NBSAC’s propeller guard subcommittee released its final report. The first recommendation was, “The U.S. Coast Guard should take no regulatory action to require propeller guards.”

This finding was in sharp contrast to USCG’s own 1987 Purcell and Lincoln study. Purcell and Lincoln found much more information needed to be gathered before such a decision could be reached.


Contributions of Dick Snyder of Mercury Marine to the NBSAC Report

Richard Snyder of Mercury Marine was not a member of the NBSAC subcommittee on propeller guards. However, several of his statements made it into the final report. Mr. Snyder was known for repeating certain statements about propeller guards over and over to the media and the industry. We refer to those statements as “Snyderisms”. One of Mr. Snyder’s statements making the final report was, “Due to its revolutions, a propeller generally produces a series of evenly spaced cuts which are relatively easier to repair surgically.” Mr. Snyder’s comment ignores several factors including bleeding to death, water born wound infection issues, amputations, the cost and challenges of prosthetics, and many surgeries being required to repair these injuries.

Another problems with the 1989 NBSAC study, was Mercury Marine knowingly supplied the propeller guard subcommittee with incorrect propeller strike data. This made the problem look much less severe than it actually was. Our report proves this repeatedly using the industry’s own documents.

The Coast Guard records accidents as a series of three events. Mr. Snyder of Mercury only reported First Event data, also known as Primary Event data. First Event data only represents a fraction of the total number of fatalities recorded in the annual U.S. Coast Guard Boating Accident Report Database (BARD).

Then Mr. Snyder subtracted 1/3 of the Primary Event accidents saying they were primarily struck by a boat vs by the propeller. Two previous USCG studies were unable to identify a single accident in which the boat was responsible for the most severe injury.

Next Mr. Snyder subtracted those accidents in which someone was struck by a propeller and drowned. Some of those individuals likely bled out and then drowned or were unable to swim due to the propeller strike.


Snyder Contributions Continued

Mr. Snyder also failed to follow the admonition of Purcell and Lincoln. They called for including propeller injury accident data along with the fatality data. Purcell and Lincoln said that in many instances, the only difference in a propeller injury accident and a propeller fatality is chance. Therefore injury accidents must be included in the analysis of propeller accidents.

USCG Definition of Primary Accident Type

USCG Definition of Primary Accident Type

The 1989 NBSAC study also focused on the increased forward facing cross sectional area of the propeller guard vs. the open propeller. When combined with their statements of propeller guard strikes being worse than open propeller strikes, this increase in cross sectional area, portrayed propeller guards / prop guards as being even worse. The claim is humorous today in view of the boating industry featuring countless boats with 3,4, or even more very large outboard motors on them. Multiple large outboards have many times more cross sectional area than added by a propeller guard on a boat powered by a single outboard motor available in 1989.

The 1989 report even says a propeller guard increases the cross sectional area of an open propeller by 3 times (300 percent). That is an example of the exaggerated claims made by the 1989 NBSAC report.


The 1990 Underwater Head Impact Study

A very large donut shaped water tank the State University of New York (SUNY) at Buffalo with a long rotating arm was used for the research project. Michael Scott was hired by Mercury and OMC’s legal departments as the lead researcher of the project. The project was to simulate propeller guard underwater impacts with a human head by using a crash dummy.

Mr. Scott admitted the NBSAC report’s reliance upon blunt trauma to reject the use of boat propeller guards was not supported by experimental data.

Scott’s research was to gather data to support the NBSAC study.

The SUNY head impact study had a lengthy list of problems. Among the most widely known problems being the spring in the crash dummy’s neck was several times stiffer than a human neck in compression. As the propeller guard traversed the dummy’s head it pushed the neck down. This resulted in much high stresses being recorded in the dummy’s neck than would be present in a human neck.

Scott mentioned the neck stiffness problem in early versions of the report. However all mention of neck stiffness issues was missing from the final version of the report.

The outboard motor was placed at zero trim (vertical leading edge) which makes it more difficult for a head to slid down the leading edge of the drive.

The outboard was also configured in a way that made the hydraulic system “stiffer” and eliminated some give in the system that could have reduced peak loads.

The head impact study even cites Event 1 statistics, years after the industry was aware this was improper.


The 1990 Underwater Leg Impact Study

Tyler Kress was hired by Mercury and OMC’s legal department as the lead researcher for the leg impact study at SUNY.

This study was conducted in the tank at SUNY in conjunction with the head impact study.

The leg impact study had a lengthy list of problems as well. One of of the most widely known problems was the use of legs from cadavers that were over 70 years old that had been embalmed for several years.

In addition the legs were impacted perpendicular to the path of the outboard motor (laid horizontally across its path). Most propeller strike leg injuries occur with the person longitudinally coming at the propeller. Such as a swimmer approaching or retreating from the propeller, or legs being in a vertical position near the propeller at the swim ladder.

The outboard motor was placed at zero trim (vertical leading edge). This makes it more difficult for legs to slid down the leading edge of the drive.

The outboard was also configured in a way that made the hydraulic system “stiffer”. This eliminated some give in the system that could have reduced peak loads.

The leg impact study even cites Event 1 statistics, years after the industry was aware this was improper.


The 1990’s

As mentioned earlier the industry quickly began to use these studies and the researchers in boat propeller guard cases. The studies and experts were extremely successful in court. They were also successful in scaring off potential litigants before they even filed legal cases.

In the early 1990’s Mercury and OMC also began perfecting their “get out of jail free card” to put an end to all these propeller cases. They claimed the U.S. Coast Guard’s failure to require all boats to have propeller guards in the 1971 Boating Safety Act established a Federal Preemption. This Federal Preemption prevented requiring propeller guards on any specific boat.

As Mercury and OMC continued to win cases based on Federal Preemption, and the precedent was set. The importance of the three propeller guard studies began to wane. Mercury and OMC basically began to just show up in court, claim Federal Preemption, win the case, and go home.

Federal Preemption was their “get out of jail free card” until the U.S. Supreme Court struck down the Federal Preemption defense in the Sprietsma vs. Mercury Marine case in December 2002.

Since then, the original three studies (the NBSAC study, the SUNY head impact study, and the SUNY leg impact study) have been regaining importance. The 1989 NBSAC report is once again the keystone of the industry’s defense. It is frequently backed up with litigation testing (industry testing of proposed alternatives in a manner to make sure they fail).

The three propeller guard reports are also touted when propeller safety regulations have are proposed by the Coast Guard. This can be seen in the 1995 Federal Register where they are used against a 1995 houseboat and displacement boats propeller safety proposal.


Boat Propeller Guard Product Liability Defense

We have completed a major project in which we studied the period in which Mercury Marine and Outboard Marine Corporation developed their legal defense against the use of boat propeller guards on recreational boats. This post is the first of five on this topic.

Their defense is based on three documents which they helped create:

  1. 1989 U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) Propeller Guard Subcommittee report
  2. 1990 Underwater Head Impact Study
  3. 1990 Underwater Leg Impact Study

The above defense was abandoned in the 1990s once their new Federal Pre-emption defense began to be accepted by the courts. However, in 2002, the U.S. Supreme Court struck down the Federal Preemption defense in the Sprietsma vs Mercury Marine case. Since then, the boating industry has returned to a product liability / product defect defense based upon the three studies listed above.

This review exposes many problems with these three studies, several of which have not been previously revealed.

Propeller Guard Study Arch with the 1989 NBSAC Study as the Keystone

Propeller Guard Study Arch with the 1989 NBSAC Study as the Keystone

As shown in the image above the 1989 NBSAC report is the keystone to their product liability defense / product defect defense against the use of boat propeller guards. It is supported by the Head and Leg Impact studies. Similarly, the 1989 NBSAC report is the keystone to their product liability / product defect defense.

Our in-depth review of these three reports, and the documents behind them, has created a great deal of materials. They are organized as shown below.


Our Findings Are Presented 3 Ways

1. For those seeking a quick overview of a portion of the information, a series of 15 charts are provided

2. For those looking for more information, an introduction post plus three more posts, one for each study were prepared

3. For those looking for the most in depth information, the four lengthy pdf reports including hundred of footnotes and copies of documents are provided


The Charts

We begin by providing links to the charts in the table below:

Volume I Charts – The Introduction

Chart 0 Index of the charts
Chart 1 USCG Propeller Guard Report by Purcell & Lincoln part 1
Chart 2 USCG Propeller Guard Report by Purcell & Lincoln part 2
Chart 3 NBSAC vs Purcell & Lincoln: Very Critical Points
Chart 4 Introduction to Mercury Marine & OMC’s Propeller Guard Legal Defense

Volume II Charts – 1989 NBSAC Report

Chart 5 1989 NBSAC Propeller Guard Subcommittee Report: Background Information
Chart 6 1989 NBSAC Propeller Guard Subcommittee: Existing Propeller Accident Statistics
Chart 7 1989 NBSAC Propeller Guard Subcommittee: Full Timeline
Chart 8 1989 NBSAC Propeller Guard Subcommittee: Findings
Chart 9 1989 NBSAC Propeller Guard Subcommittee: Epilog
Volume III – Underwater Head Impact
Chart 10 SUNY Head Impact Testing part 1
Chart 11 SUNY Head Impact Testing part 2

Volume IV – Underwater Leg Impact

Chart 12 SUNY Leg Impact Testing part 1
Chart 13 SUNY Leg Impact Testing part 2

Thoughts About This Project

Chart 14 Summary: Some Issues With These Three Studies
Chart 15 ?? What Does All This Mean?


The Four Volume Manuscript

Volume Number Title & Link to the full PDF document Link to the Post Chart Numbers
1 Introduction (1 megabyte) the post 1, 2, 3, 4
2 Review of the USCG 1989 NBSAC report (11 megabytes) the post 5, 6, 7, 8, 9
3 Review of the SUNY Underwater Head Impact Study (7 megabytes) the post 10, 11
4 Review of the SUNY Underwater Leg Impact Study (2.5 megabytes) the post 12, 13
none Summary/Conclusion Charts none 14, 15


Comments: Yours and Ours

We spent a great deal of time in completing this set of documents. We hope you find them useful.

If you have any comments, please place them one of the four post pages. Links to them are provided in the 4 Volume Manuscript table above.


1989 NBSAC Propeller Guard Subcommittee Report Vol2

This post is the third of a series of five posts covering the boating industry’s legal defense against boat propeller guard product liability / product defect lawsuits. It focuses on our review of the 1989 U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) Propeller Guard Subcommittee report.

This post is a condensed version of a lengthy pdf report titled Mercury Marine & Outboard Marine Corp. Propeller Guard Case Legal Defense Volume II: The 1989 NBSAC Study that can be found at Boat Propeller Guard Product Liability Defense.

As seen in the image below, the 1989 NBSAC report became the keystone of the boating industry’s legal defense against recreational boat propeller guard product liability / product defect cases.

The introduction to the U.S. Coast Guard’s 1989 National Boating Safety Advisory Council Subcommittee report is copied from Volume II below.


Propeller Guard Study Arch with the 1989 NBSAC Study as the Keystone

Propeller Guard Study Arch with the 1989 NBSAC Study as the Keystone

A Brief Introduction to Our Review of the 1989 NBSA Propeller Guard Subcommittee Report

For reasons detailed in the introduction of this four volume series, Mercury Marine / Brunswick and Outboard Marine Corporation (OMC) were facing serious problems on several fronts concerning boat propeller guards about 1988-1991. These challenges forced these two fierce competitors to work together against the financial threat of propeller injury cases.

Along came the U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) in May 1988 announcing they were going to study issues surrounding the use of propeller guards.

Mercury and OMC each had an employee serving on NBSAC. Both men were chosen to serve on NBSAC’s propeller guard subcommittee.

The subcommittee was formed of 5 to 7 men and lasted about a year and a half. Mercury’s representative was Roy Montgomery, their corporate lawyer. OMC’s representative was Richard Lincoln their Director of Public Relations and Director of Environmental Affairs.

In addition to the members above, Richard “Dick” Snyder, long time in house expert witness in boat propeller strike cases for Mercury Marine, attended all three subcommittee meetings, presented at all three meetings, rebutted presentations by others, and sent numerous letters to subcommittee chairman, Jim Getz. Dick Snyder also provided propeller accident statistics to the subcommittee. Mr. Getz was a police captain with Illinois Department of Conservation acting as commander of Lake Michigan enforcement operations.

What Was the 1989 NBSAC Report Worth to the Boating Industry

A finding against use of propeller guards by the NBSAC subcommittee could be worth millions of dollars to Mercury and OMC. The full National Boating Safety Advisory Council and U.S. Coast Guard would likely ratify the subcommittee’s findings. A Coast Guard statement against use of propeller guards could quickly be wielded by Mercury and OMC in boat propeller cases, in the media, and in public debate. “Independent” findings of the U.S. Coast Guard would have tremendous weight in court against Plaintiff’s saying boat motors should have propeller guards. That is in fact what happened.


Three Previously Unexplored Problems With the Report

This volume explores three previously unexplored problems with the 1989 NBSAC subcommittee on propeller guards final report.

Problem #1: the subcommittee was knowingly furnished inaccurate, watered down propeller accident statistics by Mercury Marine.

Problem #2: “Snyderisms – several points frequently made by Dick Snyder, Mercury Marine’s long term in house propeller accident expert witness, made it into the report without being proven or even being attributed to him. Later on, Mercury was able to quote his unattributed statements from the 1989 NBSAC study, giving them even more authority.

Problem #3: Dick Snyder presented Mercury’s project with U.S. Marine Corps to produce propeller guards for Outboard Marine Corporation (OMC) outboard motors as a failure. That was not true.

This volume will cover each of these three problems separately.


Underwater Head Impact Propeller Guard report Volume3

This post is the fourth of a series of five posts covering the boating industry’s legal defense. Specifically, their legal defense against boat propeller guard product liability / product defect lawsuits. It focuses on our review of the 1990 underwater testing of a propeller guard impacting an anthropomorphic dummy’s head. The testing was performed at State University of New York at Buffalo by Mercury Marine and OMC.

This post is a condensed version of a lengthy pdf report titled Mercury Marine & Outboard Marine Corp. Propeller Guard Case Legal Defense Volume III: Head Impact Study. The materials can be found at Boat Propeller Guard Product Liability Defense.

The importance of the 1990 Head Impact study is shown in the image below. It was used by the boating industry to support the 1989 NBSAC study. Without the head impact study, the 1989 NBSAC keystone study would fall. Their legal defense against recreational boat propeller guard product liability / product defect cases relies upon it.

The introduction to the our review of the 1990 Head Impact Study report is copied from Volume III below.


Propeller guard legal product liability defense arch. Shows the underwater head impact testing at SUNY as a column supporting the 1989 NBSAC keystone study.

Propeller guard legal product liability defense arch. Shows the underwater head impact testing at SUNY as a column supporting the 1989 NBSAC keystone study.

A Brief Introduction to Our Review of the 1990 Head Impact Study

One version of Mike Scott’s Head Impact Paper

As mentioned in previous volumes, 1988 – 1991 was an especially difficult time for Mercury Marine and Outboard Marine Corporation (OMC). Several propeller injury lawsuits were being filed against them. Plaintiffs claimed Mercury and OMC drives should have propeller guards.

Mercury and OMC had a mutual protection relationship in trying to find relief from these lawsuits. Relationships were being formed prior to May of 1988 when the US Coast Guard National Boating Safety Advisory Council (NBSAC) formed a propeller guard subcommittee.

Mercury and OMC both had representatives on the subcommittee. In addition, Dick Snyder, Mercury’s long time expert witness in boat propeller cases was closely involved with the subcommittee.

Mercury and OMC were also involved in a propeller guard project for the U.S. Marine Corps in this era. See Volume II.

Dick Snyder testified underwater propeller guard impact studies grew from a discussion he had with John Snider and Peter Fuller at a seminar on injuries. Snyder was talking with them about their work with cadavers and motorcycle accidents, and the potential to do similar research underwater.


Boat Propeller Guard Testing at SUNY

State University of New York (SUNY) at Buffalo has a 200 foot in circumference donut shaped pool. It was originally constructed for testing humans in special environments. The facility is known as the Center for Research and Education in Special Environments (CRESE).

The boating industry has since used the facilities for several propeller guard studies.

If you are unfamiliar with tank at SUNNY see the video in the introduction or read any of the studies performed there.

Data for the head impact study was collected in December 1990, along with the leg impact data discussed in Volume IV.

Together, these two studies support the 1989 NBSAC subcommittee on propeller guards report as seen on the cover page of this volume.


Underwater Leg Impact Propeller Guard report Volume4

This post is the fifth of a series of five posts covering the boating industry’s legal defense. Specifically, their legal defense against boat propeller guard product liability / product defect lawsuits. It focuses on our review of the 1990 underwater testing of a propeller guard impacting cadaver legs. The testing was performed at State University of New York at Buffalo by Mercury Marine and OMC.

This post is an introduction to a lengthy pdf report titled Mercury Marine & Outboard Marine Corp. Propeller Guard Case Legal Defense Volume IV Leg Impact Study. The materials can be found at Boat Propeller Guard Product Liability Defense.

As seen in the image below, the 1990 Leg Impact study was used by the boating industry to support the 1989 NBSAC study. Without the leg impact study, the 1989 NBSAC keystone study would fall. The boating industry’s legal defense against recreational boat propeller guard product liability / product defect cases relies upon it.

The introduction to the our review of the 1990 Leg Impact Study report is copied from Volume IV below.


Propeller guard legal product liability defense arch. Shows the underwater leg impact testing at SUNY as a column supporting the 1989 NBSAC keystone study.

Propeller guard legal product liability defense arch. Shows the underwater leg impact testing at SUNY as a column supporting the 1989 NBSAC keystone study.

A Brief Introduction to Our Review of the 1990 Head Impact Study

One version of Tyler Kress’ Leg Impact Paper

1988 – 1991 was an especially difficult time for Mercury Marine and Outboard Marine Corporation (OMC). A multitude of propeller injury lawsuits were being filed. The suits claimed their drives should have had propeller guards.

Mercury and OMC had a mutual protection relationship in trying to find relief from these lawsuits. Then along came the U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) forming a propeller guard subcommittee in May of 1988.

Mercury and OMC both had representatives on the NBSAC subcommittee on propeller guards. Dick Snyder, Mercury’s long time expert witness in boat propeller cases was also closely involved with the subcommittee.

Mercury and OMC were also involved in a propeller guard project for the U.S. Marine Corps in this era.

Dick Snyder testified underwater propeller guard impact studies grew from a discussion he had with John Snider and Peter Fuller at a seminar on injuries. He was talking with them about their work with cadavers and motorcycle accidents and the potential to do similar research underwater.

The State University of New York (SUNY) at Buffalo has a large circular pool. It was originally constructed for testing humans in special environments. The facility is known as the Center for Research and Education in Special Environments (CRESE).

The boating industry has since used the facilities for several propeller guard studies.

If you are unfamiliar with the tank at SUNNY see our video in the Introduction or read any of the studies performed there.

Data for the leg impact study, discussed in this volume, and the head impact study discussed in Volume III were both collected in December 1990.

Together, these two studies were intended to support the 1989 NBSAC subcommittee on propeller guards study as seen in the image above.

California woman struck by boat propeller in Columbia

Natalia Andrea Larranaga Fajardo, 26 originally from Columbia, now from California, was on vacation in Columbia on November 27, 2022.

Natalia Andrea Larranaga Fajardo<br>Daily Mail image

Natalia Andrea Larranaga Fajardo
Daily Mail image

Natalia was on Wata Beach in San Andes, Columbia about 445 miles off the mainland coast of Columbia. She saw some people she knew on a tour boat and joined them. The tour boat was carrying 22 tourists and two crew members. It went to a popular area with several other boats. Natalia’s flip-flops / thongs/ sandals fell over the side of the boat. Natalia dove in to recover her flip-flops and was fatally struck by the tour boat’s propeller.

She was struck in the legs, lower back, and buttocks by the propeller. Natalia was taken by jet ski (PWC) to a hospital on San Andres Island. The name of the hospital was the State Social Enterprise Department Hospital. She received several transfusions and surgeons tried to repair her arteries. Natalia died from cardiac arrest early the next morning.

Cell phone video covered the moments after the accident. Most sites are marking it as UPSETTING OR DISTRESSING VIDEO as it is graphic.

The accident is under investigation in Columbia.


Discussion of Media Coverage

The accident was internationally covered by media such as NewsHub (New Zealand), the Daily Mail (UK), Yahoo News, Daily Beast, Meaww, Daily Star (UK), The Sun (UK), First Post (India), Miami Herald, Mirror (UK), Must Share News, Daily Caller, MSN, New York Post, Archipelago Press, News.Com Australia, Toronto Sun (Canada), and SK Pop news.

The international press deadlines were very graphic such as “shredded by boat propeller”, “gruesome boating death and witnesses scream in horror”. “tourist gruesomely killed by boat propeller”, “shredded to death in boat propeller turning sea red with blood”, “dies after being sucked into boat propeller”, and “gets shredded by boat propeller”.

As usual, U.S. headlines were considerably more reserved.


Reduce Peak Impact Force of Boat Propeller Guards

This Tech Brief explains a method that may reduce maximum impact force of some boat propeller guards striking people.

This method may also:

  1. Reduce injuries caused by striking some boat propeller guards at lower speeds.
  2. Allow some propeller guards to be operated at higher speeds while causing less severe injuries to people in the water.

Propeller Safety Tech Brief #1



Note this material is NOT professional advice.

It is meant to stimulate discussion & encourage further development
of this potential approach.


Brief Description of Method

This approach uses two-stage hydraulic tilt cylinders to reduce peak impact forces between boat propeller guards and people in the water.

Outboard motor trim and tilt graphic

Outboard motor trim and tilt graphic
Derived from a Yamaha graphic

An example of how an outboard motor trims, then can be tilted up for trailering.

Outboard motors with hydraulic tilt and trim (many outboards of forty horsepower or more) use a hydraulic cylinder to raise and lower the outboard.

The tilt up for trailering segment is also used when an outboard motor with power tilt & trim strikes a rock. The outboard motor strikes a large log, it tilts up while its energy is dissipated by relief valves in the tilt cylinder. Use of a two stage cylinder instead of a traditional tilt cylinder allows the outboard motor to flip up and over the object with minimal resistance. Then the two stage tilt cylinder begins to cushion the upward swing of the outboard. As a result there is a significantly softer impact with the log.


Objections to Propeller Guards Based on Blunt Trauma

Page 20 of the 1989 U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) propeller guard subcommittee report states, “Proponents assert that propeller guard technology and/or availability meets the foregoing criteria and that guards should be mandated. The subcommittee does not agree and offers the following comments:”

    … “Masks with wide mesh or spaced bars and ring guards may prevent cuts from body contact with a propeller but substitute the potential of blunt trauma injury, which becomes increasingly significant at speeds over 10 mph, leading to an ascending serious risk of fatality as speeds increase.”

The boating industry has long stated blunt trauma is a major reason for limiting boat propeller guards to a certain maximum speed such as 2, 5, 10, or 15 miles per hour.


1989 U.S. Coast Guard National Boating Safety Advisory Council (NBSAC) Propeller Guard Subcommittee Report

Blunt trauma issues were not proven by the 1989 NBSAC report. However, it is apparent that being struck by a propeller guard at speed is bad. Even without a propeller guard, if a person strikes the the outboard motor and somehow avoids being struck by the propeller, they can still be seriously injured or killed at speed.


Underwater Head Impact Testing at SUNY in late 1990

Outboard Marine Corporation and Mercury Marine funded an investigation into a propeller guard striking heads underwater. They used:

  1. A specific propeller guard invented by Dick Snyder of Mercury Marine,
  2. a special water facility at State University of New York at Buffalo,
  3. and a crash dummy to conduct the underwater tests.

Several impacts were conducted in the manner seen in the image below in late 1990.

SUNY Propeller Guard Test Dummy

SUNY Propeller Guard Test Dummy

Conclusions of the resulting technical paper, “Injury Analysis of Impacts Between A Cage-Type Propeller Guard and a Submerged Head” coauthored by the lead researcher Michael W. Scott, include:

“The results of this study support the argument of the NBSAC report that blunt trauma injuries may become significant at speeds greater than 10 mph.”

Note the statement above is not very definitive due to the use of phrases like “support the argument” and “may become significant”.


Comparison of the 1989 NBSAC Report and the Head Impact Report Regarding Propeller Guard Top Speeds

The 1989 NBSAC report Biomechanical considerations section on pages 17 and 18 of their report stated:

“It was repeatedly stated that a skull impact of 10 mph or more in the water would generally be fatal.”

However, they cite no individuals or references as supporting the statement above.

The 1989 NBSAC report also states:

“Even with an idealized cushioning material, not currently known to exist, head or body cavity strikes at speeds over 10mph could likely be fatal.”

Again, no individual or reference is cited regarding the statement above.
In addition the use of “could likely” is very indecisive.


Need for a Solution

The NBSAC and Head Impact studies are basically saying fatalities become a major problem in propeller guard head impacts at speeds above 10 miles per hour.


Define the Problem

Mitigate propeller strike injuries due to peak impact forces, including those at speeds greater than 10 mph.

There are obviously other concerns about specific propeller guards on specific boats as speeds increase including: boat handling issues, drag, fuel consumption, and emissions.

This Tech Report only focuses on reducing peak impact forces.


The Existing Log Strike System – Typical One Stage Tilt Cylinder

Tilt cylinders have long been around to protect the outboard motor. They can prevent outboard motors from breaking off when striking obstacles such as rocks or floating logs.

Normal tilt cylinders typically have hydraulic relief valves (balls and springs) retained within the cylinder piston. The relief valves cushion the upward swing of the outboard motor when it strikes floating debris and the cylinder rod extends.

A typical single stage tilt cylinder is shown below.

Trim Cylinder Design for Log Strike

Trim Cylinder Design for Log Strike


History of Two Stage Tilt Cylinders

Sometimes one stage tilt cylinders restrict the upward swing of the outboard motor too much before it clears the object and the outboard motor breaks off.

Thus, two stage hydraulic cylinders were designed to solve this problem.

We have never seen their use on a production outboard motor, likely due to them costing a little more. Outboard motor manufacturers are very cost sensitive.

Two stage cylinders are designed to provide minimal resistance to the upward swing of the outboard motor until it clears the obstacle. Then they apply significant resistance to the upward swing of the outboard motor until it stops or reaches the top of its swing. The outboard motor then settles back down to its original trim position.


Historical Two Stage Hydraulic Tilt Cylinder Patents

Many outboard manufacturers and some third party suppliers previously developed and patented two-stage tilt cylinders for outboard motors including:

  1. Outboard Marine Corporation
  2. Yamaha/Sanshin
  3. Carl Kiekhaefer of Kiekhaefer Corporation which became Mercury, then Mercury Marine
  4. Charles Alexander of Kiekhaefer Corporation
  5. Volvo Penta
  6. Brunswick / Mercury Marine
  7. Parker-Hannifin
  8. Showa (well known Japanese manufacturer of tilt cylinders for outboard motors)

Some use a spring around the cylinder rod inside of the cylinder to time when a washer will begin to cover over some or all of the relief valve inlets. The spring method sometimes simultaneously creates a more tortuous path through some of the relief valves that increases the relief valve pressure as the cylinder rod extends. Another feature is some of the relief valves can have a higher pressure setting than others. The relief valves with a lower setting can be covered up by the washer only leaving the relief valves with the higher setting open to flow after the outboard clears the object.

References

  1. “Approaches to Prevent Outboard Motors From Flipping Into Boats After Striking Floating or Submerged Objects. 2018. Pages 28-38.
  2. “Approaches to Prevent Outboard Motors From Flipping Into Boats After Striking Floating or Submerged Objects. Supplement #1. 2020. Pages 5-7.

Mercury Marine Modern Two-Stage Hydraulic Tilt Cylinders

Mercury Marine showed a two-stage hydraulic tilt cylinder design in a 2017 presentation to the Western Dredge Association. Clips from pages 14 and 15 of that presentation are shown below.

Mercury Marine two-stage hydraulic cylinder assembly

Mercury Marine two-stage hydraulic cylinder assembly

Mercury Marine two-stage hydraulic cylinder components

Mercury Marine two-stage hydraulic cylinder components


Recent Brunswick Patent for Digitally Controlled Two-Stage Hydraulic Tilt Cylinder

Brunswick patented a two stage cylinder using magnetic fluid that allows it to dynamically respond to log strikes (and human strikes). An electric charge adjusts the viscosity of the tilt cylinder fluid exiting the rod end of the tilt cylinder allowing the fluid itself to act as a virtual relief valve. The system can act as a two stage hydraulic tilt cylinder by reducing the pressure in the rod end of the cylinder as the fluid escapes until it clears the object.

The magnetic fluid system then shifts to a higher virtual relief valve setting until the upward swing of the drive is halted. This system can be controlled by the Engine Control Unit (ECU) allowing it to make decisions based upon multiple variables. See the images below:

Operational chart for Brunswick two stage magnetic fluid hydraulic tilt cylinder

Operational chart for Brunswick two stage magnetic fluid hydraulic tilt cylinder

Below is a chart showing some of the variables Brunswick’s magnetic tilt cylinder can take into account as it maps out the best way to handle a specific impact.

Brunswick two stage magnetic fluid hydraulic tilt cylinder patent

Brunswick two stage magnetic fluid hydraulic tilt cylinder patent


Another Recent Brunswick Patent for a Digitally Controlled Two Stage Cylinder

Brunswick also recently patented a digitally controlled hydraulic tilt cylinder using normal hydraulic fluid. It includes feeding back the amount of extension of the cylinder rod (its position) which can also be used to dynamically calculate the position of the cylinder piston. This design also includes a hydraulic brake that can be used to prevent the cylinder rod from extending when the drive is operating in reverse. It also provides additional resistance to the upward swing of the outboard motor after it clears the object. See the image below.

Brunswick hydraulic tilt cylinder with position feedback

Brunswick hydraulic tilt cylinder with position feedback

This position sensing version of a hydraulic tilt cylinder also has an operational chart fairly similar to the chart for the two stage tilt cylinder using magnetic fluid.

Normal tilt cylinders must have their internal relief valve set high enough to prevent the drive from trimming out in reverse.
Digital tilt cylinders have many options to prevent the tilt cylinder from trimming out in reverse.


Sanshin / Yamaha Two Stage Cylinder Patent Drawing Shows Lowering of Peak Impact Force

A Japanese Sanshin / Yamaha patent for a two stage tilt cylinder provided the force vs. time graph below.

Sanshin (Yamaha) two stage outboard motor tilt cylinder patent drawing graph

Sanshin (Yamaha) two stage outboard motor tilt cylinder patent drawing graph

The graph above shows the peak impact force for a traditional outboard tilt cylinder is much greater (the solid line) than that of a two stage tilt cylinder (the dotted two humped curve).

The two stage cylinder quickly lets fluid out of the rod end of the cylinder when an object is struck, then begins to resist the upward swing of the outboard as soon as the object is cleared by the outboard.


The Solution to Reducing Propeller Guard Impact Forces

Use two stage cylinders in combination with propeller guards to reduce peak forces and accelerations to humans struck in the water while underway.

Humans may be lighter than logs, but they can still activate the log strike system when they are struck, especially when struck by smaller outboards at modest speeds.

Two stage cylinders provide minimum resistance to the outboard swinging upward until the outboard clears the human.

The new digital two stage tilt cylinders for outboard motors offer on most countless ways of making this system even better. For example you know when the system is underway in reverse. The system could run with an extremely low relief valve setting when they vessel is not underway in reverse. Larger outboards would need a higher relief valve setting to cover running in rough water or being airborne and re-entering the water.


What Type of Propeller Guards Might Benefit the Most From The Use of Two Stroke Cylinders

Dick Snyder Propeller Guard Patent Sketch

Dick Snyder Propeller Guard Patent Sketch

Some propeller guards wrap around the front on the lower leading edge of the outboard motor. Examples include:

  1. Cage type guards that actually wrap around the lower leading edge of the drive, such as Dick Snyder / Mercury Marine’s propeller guard as shown at right.
  2. Vane type propeller guards like those built by MidCoast Marine.
  3. More conventional looking cage type propeller guards like those built by Propeller Guard Technologies. Their drives are tied to the outboard motor. The outboard motor and the propeller guard are basically one piece.

Mike Scott’s data from the SUNY head impact studies can be seen in an earlier volume of his report. The data shows the drive partially swinging up via an accelerometer placed at the rear of the torpedo at higher impact speeds. The same effect can be seen with lower peak accelerations for off center strikes. Minimal upward swing is visible in the videos accompanying the SUNY head impact tests.

Scott’s testing results were more severe than would actually occur in the field for multiple reasons. Among them was they trimmed the outboard motor down against a trim limit peg and built up the rod end pressure to the relief drive pressure before every test run. They said they did it to represent propeller force. By pre-charging the rod end of the cylinder to the relief valve pressure there was no longer a brief cushion while that pressure built up when a person was struck. This increased the acceleration of the head when it was struck.


Additional Benefits

  1. The use of two stage tilt cylinders can reduce damage to propeller guards when grounding or striking rocks while underway.
  2. The use of two stage tilt cylinders can help prevent outboard motors from breaking off and flipping into boats at higher speeds.
  3. Improve the life of marine drives by reducing peak impact forces.
  4. The use of digitally controlled two stroke cylinders (like the two Brunswick digitally controlled hydraulic tilt cylinders shown earlier) brings almost endless possibilities and features, including running with the equivalent of pressure relief valves set at near zero.

Testing

This Tech Brief is very general.

It will take considerable effort to test this approach.

That testing might be significantly sped up if researchers had access to a dry land impact test stand like the one at Mercury Marine.

The method will likely prove to be most effective on smaller outboard motors.


Wrapping Things Up

We considered calling the use of two stroke cylinders to reduce peak force when a person is struck by a propeller guard an invention.

We did not because the boating industry developed this approach over 50 years ago to prevent the outboard motor from breaking off when it struck a log or rock.

To our knowledge, two stage hydraulic tilt cylinders never made it to production, but almost everybody developed one at one time of another.

Recent developments in this field by Brunswick may finally bring them into production.


April 28, 2023 Update

Rental Pontoons Boats, Rental Houseboats, & SOLAS Tender Applications

Two-stage tilt cylinders may prove to be especially adaptable to rental pontoon boats and rental houseboats with top speeds faster than those currently considered for adapting cage type propeller guards. Two-stage tilt cylinders not only have the capability of reducing peak impact forces to people in the water, but also provide protection to the propeller guard and outboard motor when striking rocks or hitting bottom while beaching.

Two-stage tilt cylinders may also be applicable to outboard motors powering SOLAS (Safety Of Life At Sea) tenders. These Rigid Inflatable Boats (RIBS) on larger yachts are used to transport people, supplies, and trash to and from shore while doubling as a rescue boat. SOLAS standards require them to have a propeller guard. SOLAS tenders range from smaller outboards up to about 150 horsepower and typically go faster than displacement pontoons or houseboats. SOLAS certification of outboard motors covers several items including requiring a propeller guard. Mercury Marine and Yamaha are among the manufacturers producing SOLAS certified outboard motors.


Comments

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Malibu Appeals $200 million verdict in Batchelder case

A quote from Malibu’s August 15, 2022 appeal in the Batchelder case is below:

“Defendant Malibu Boats, LLC herby appeals to the Court of Appeals of the State of Georgia from the Final Judgement entered on August 28, 2021 including all adverse ruling sustained therein and all subsequent adverse rulings including but not limited to ….”

The Superior Court of Rabun County Georgia reaffirmed the original August 2021 verdict on July 18, 2022 and informed Malibu they had 30 days to appeal, which Malibu did on August 15, 2022.

This legal case resulted from the July 17,2014 death of 7 year old Ryan Batchelder on Lake Burton in Georgia.

Clark, Fountain, La Vista, Prather & Littky-Rubin represented the Batchelder family. Their press release after the initial verdict was rendered discusses some of the earlier history of the Batchelder case.

A major element of the case was Malibu’s awareness of certain open bow ski boats taking water over the bow. We recently published an article showing how boat manufacturers can use several of the tools we have placed online to monitor the post sale safety of their products and take action when safety issues arise vs. waiting til they are sued.


Batchelder vs. Malibu: Monitoring Post Sale Safety

The $200 million dollar verdict in Batchelder vs. Malibu Boats was reaffirmed July 18, 2022. One reason for such a large verdict was Malibu’s lack of a Post Sale Safety Monitoring system in which they actively sought out accidents involving their boats and addressed Post Sale safety issues.

An order by the Judge denied the various points raised by Malibu against the original verdict.

One of those points was that Malibu was not allowed to bring up in trial that there were no previous similar accidents.

Prior to the trial the judge heard a long list of things from both sides that each side would like to keep out of the trial.
In this instance the judge ruled Malibu would not be able to bring up there were no previous similar accidents AND Plaintiffs would not be able to bring up previous Malibu accidents.


Some Sources of Boat Post Sale Accident / Incident Data

Polson Enterprises was involved in identifying previous water over the bow Malibu accidents in BARD (the U.S. Coast Guard Boating Accident Report Database), in the news media, in social media, in the Malibu Crew online forum, even back in the days of USENET rec.boats and rec.sports.waterski, and otherwise available to Malibu.

While that information did not make it into the actual trial, the judge mentioned it in the order addressing issues raised by Malibu.

Open Bow Photo from Malibu-Axis Owners Facebook Page

Open Bow Photo from Malibu-Axis Owners Facebook Page

Note, our coverage of other elements of the Judges Order is at Batchelder vs Malibu: $200 million jury verdict stands.

The portion of the order pointing out Malibu’s lack of Post Sale Monitoring of Product Safety is contained within pages 71-73 of the link provided by Clark, Fountain, LaVista, Prather & Littky-Rubin, the legal firm representing the family along with Drew Ashby at the Ashby Firm, now known as ATL.

This post begins with quotes from the judges order. It ends with tools that can help boat manufacturers monitor the safety of their boats in the field. Post Sale Monitoring allows boat builders to build safer boats and document their efforts. Read More →

Batchelder vs Malibu: $200 million jury verdict stands

This case arose from a 2014 propeller strike in Georgia in which water came over the bow of a 2000 Malibu Response LX rental ski boat when it crossed its own wake. Seven year old Ryan Batchelder was washed out of or jumped from the bow and was fatally struck by the boat’s propeller. More details on the history of this case are near the end of this post.

In August 2021, the jury found Malibu guilty, awarding a total of $200 million.

Among issues in the case was Malibu’s failure to warn boat owners after Malibu knew of the hazard (2000 Malibu Response LX taking water over the bow).


Malibu Moved for New Verdict or New Trial

In September 2021, Malibu moved for a new verdict or a new trial. Issues raised by Malibu at this time included their view that Malibu LLC was not a continuation of Malibu West, they thought the punitive award was excessive, Malibu owed no duty to Ryan Batchelder, Malibu was not allowed to bring up there were no similar accidents, and more.

Both sides have been asserting their respective positions to the court since September 2021.

On Monday July 18, 2022, the court ruled on the motions and issues raised by Malibu.

The court stated, “These matters came to a hearing on May 26, 2022. After considering the parties’ written submissions, the arguments of the parties, the Court record, and all other matters proper, Malibu LLC’s action is hereby DENIED.” Read More →