PropellerSafety.com

Archive for April 2012

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).


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

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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→

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

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