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Archive for Testing Propeller Guards

Virginia Tech researchers have been studying ways to make drones safer, including simulating drones crashing into humans. Drones share air space with humans, just like boats share water space with humans.

Drone impact testing

Drone impact testing

Virginia Tech released the video above on YouTube 6 January 2017.

While recreational drones crashing into humans is relatively recent event, boats have been doing it since the days of Noah. Boats, outboard motors, propellers, and propeller guards have been impact tested against a range of objects to simulate human impacts, including anthropometric dummies and cadavers. Read More→

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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:

  • Speed
  • Maneuverability
  • Ease of Installation
  • Effectiveness

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→

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CED Propeller Guard Testing @ SUNY

CED Propeller Guard Testing @ SUNY

USCG released the new Propeller Guard Test Procedure / Propeller Guard Test Protocol earlier this week on September 11, 2013.

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→

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Many years in the making, the United States Coast Guard (USCG) released the final version of the Propeller Guard Test Procedure / Protocol today, September 11, 2013.

The US Coast Guard news release quotes USCG’s Phil Cappel as saying, “The report provides the means to evaluate the boat performance characteristics and the level of protection of personnel in the water resulting from the installation of a propeller guard on a particular sterndrive or outboard-powered recreational boat.”

USCG Propeller Guard Test Protocol

USCG Propeller Guard Test Protocol

One interesting note, the release says the test equipment required to conduct the testing will be loaned out on a first come, first served basis for the cost of shipping and insurance.

The procedure is scheduled for review in about 3 years, or earlier if necessary. Read More→

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The boating industry promotes one standard for testing propeller guards in court cases or when evaluating propeller guards proposed by those outside the boating industry, and a different standard when their own propeller guards are being tested.

They want to test your guards trimmed full under at speed with the same propeller used on the boat in the unguarded condition, but they want to test their guards at optimal trim with a reduced pitch propeller.

Test Your Guards Trimmed Full Under

In a typical propeller guard court case, the prosecution presents an exemplar propeller guard, a propeller guard they say would have prevented the accident or lessened/mitigated the victim’s injuries. The industry then tests that guard, sometimes called litigation testing. During those tests, the industry typically tests the performance of the boat with and without guard (acceleration, top speed and handling issues) with the drive trimmed all the way down. Even without a guard, several boats have handling issues with the drive trimmed full under at speed, plus they use a lot more fuel as they plow through the water. The prop tries to push the bow of the boat down, resulting in bow steering issues (harder to steer, may dart to one side or the other on its own, high steering torques, etc.). Ring type and cylindrical ring type propeller guards create loads on the drive/boat as they try to orient themselves to be parallel to the oncoming water. As a result, some ring and concentric ring propeller guards may create bow steering issues when trimmed full under at higher speeds. Read More→

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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).


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As outboard motors began to increase in horsepower, speeds went up, and striking submerged objects became more dangerous. Manufacturers designed systems to handle the loads created from striking logs or other submerged objects, and ways to test those systems.

We (PGIC) cover log strike testing because the industry often uses log strike tests to evaluate propeller guards, most notably as a defense against the use of guards in propeller injury legal cases.

Part 2 of this post, Log Strike Testing Part 2 covers the testing of these systems at Mercury Marine.

Before we cover the history of log strike testing (in Part 2), we will first explain:

  • Variables and Dynamics of a Log Strike
  • Log Strikes With Manual Trim Systems
  • Conventional Shock Absorbers as Log Strike Systems
  • Hydraulic Trim Systems Are Challenged by Log Strikes
  • Trim Cylinder Design for Absorbing / Cushioning Log Strikes
  • Trim Cylinder Relief Valve Spring Rates and Preloads
  • Trim Cylinder and Outboard Shock Absorber Patents

Read More→

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A Discussion of the History of Log Strike Testing at Mercury (Kiekhaefer Corporation), Kiekhaefer Mercury, and Later at Mercury Marine, a Brunswick Company

Please be sure to review Part 1 before reading this section. In Log Strike Testing Part 1: Log Strikes and Log Strike Systems we review what happens during a log strike and systems designed to dissipate these impact loads.

Here in Part 2 we discuss methods used to test log strike systems to make sure they are properly designed to accommodate loads generated at maximum design speeds, that production units meet those design criteria, and that accessories (like propeller guards) do not cause issues during log strikes. Read More→

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Log strike tests have long been used by Mercury to prove their outboards and stern drives could survive the impact of striking submerged logs and other floating or submerged obstacles. In the original log strike tests, Mercury’s test crew used concrete weights to position telephone poles horizontally in open water, then ran boats over them. One of these early tests is documented in a Mercury (then built by Kiekhaefer Corporation) video prepared for Mercury distributors and dealers.

We (PGIC) cover log strike testing because the industry often uses log strike tests to evaluate propeller guards, most notably as a defense against the use of guards in propeller injury legal cases.

This early log strike test video surfaced when we began doing some research surrounding the Estate of David Paul McFarlin and Jamie Laass vs. Brunswick Corporation (Mercury Marine and Lund Company) and Others case in which a family boating outing ran over a dredge pipe, a Mercury Marine outboard flipped back up into the boat, and a young boy was killed by the propeller. As I started searching for more information about log strike tests, I found this old Mercury log strike test video.

Mercury Log Strike Test

Mercury Log Strike Test

Read More→

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Effectiveness of Propeller Guards

CED Propeller Guard Testing @ SUNY

CED Propeller Guard Testing @ SUNY

About 2006 the U.S. Coast Guard began consulting and contracting with some experts to produce a test protocol for propeller guards. The American Boat and Yachting Council (ABYC) and CED Investigative Technologies are now finalizing that process for USCG. CED Investigative Technologies is a forensic engineering and accident reconstruction firm specializing in providing legal support to legal firms, insurers, and manufacturers.

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→

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