Archive for log strike

We have previously written extensively on log strike testing, the variables involved, and more specifically on trying to prevent outboard motors from breaking off and entering boats after striking floating or submerged objects.

This installment focuses purely on durability testing of prototype outboards. It does NOT address the issue of outboard motors breaking off and flipping into boats, the need to make sure production outboards maintain the same durability, production quality control issues, design changes, or other issues. It purely focuses on developing a test stand and a test protocol to test a single prototype outboard motor for durability in striking floating or submerged objects.

Note – the Asian outboard manufacturers tend to refer to log strike testing by the phrase, driftwood testing.

Note – Log strike testing is DANGEROUS, please read the DISCLAIMER at the bottom of this post.

This post is not meant as a “pick one” offering. It is more of buffet from which manufacturers new to log strike testing consider picking some things if they like them and bring some of their own ideas to the table as well to create something that works for them at the stage they are now in.

On Water Log Strike Testing

Most major outboard manufacturers now have a log strike test procedure in place for durability testing of outboard motors. Some still perform on water testing by running flat bottomed boats over floating logs.

Log strike testing news clip. Corpus Christie Caller-Times. 30 April 1960. Page 6D.

Log strike testing news clip. Corpus Christie Caller-Times. 30 April 1960. Page 6D.

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Rex Chambers' boat with outboard motor broke off

Pro angler, Rex Chambers’ boat with outboard motor broke off

When outboard motors strike submerged objects they can break off and flip into the boat as seen in our lists of outboard motors breaking off and flipping into boats and large outboard motors breaking off and flipping into bass boats.

We previously posted information on several existing and proposed solutions, including The Leash, a vectran tether targeting bass boat applications.

Submerged objects have a wide range of characteristics ranging from almost pure water with just a few weeds or small pieces of debris all the way up to stumps, pilings, dredge pipes, railroad ties, and concrete piers. When outboard motors from various manufacturers of various sizes and speeds strike this wide range of objects, the outboard motor log strike system behaves in a number of different ways (modes).

Especially of interest are outboard motors that break off the boat. Breaking off the boat is a prerequisite to breaking off and flipping into the boat. Not all outboards that break off will flip into the boat. But for an outboard to pass over the rear deck, and enter the seating area of a bass boat, it must first break off the boat.

The Outboard Motor Log Strike Modes Chart for a bass boat below illustrates the range of behaviors (modes) encountered.

Outboard Motor Log Strike Modes

Outboard Motor Log Strike Modes

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Edwin Evers celebrating winning Bassmaster Classic 2016 Mercury Marine image

Edwin Evers celebrating winning Bassmaster Classic 2016
Mercury Marine image

We were privileged to attend the 2016 Bassmaster Classic on Grand Lake with the weigh-ins in Tulsa, Oklahoma on March 4-6, 2016.

Edwin Evers, a local professional bass fisherman came from behind on day 3 to win the tournament.

We just noticed Mercury issued a press release back on 8 March 2016 about the Evers win and about him using their Mercury 250 Pro XS outboard motor.

We congratulate Mercury on being on the winner’s boat.

While at the tournament we noted the presence of technical support crews and trucks from various manufacturers associated with the event, including Mercury.

Near the end of the press release, Mercury tells of the reliability of their outboard and of the contribution made by their tech support crew when Edwin Evers struck a log on day 2 (Saturday).

Mercury Marine
portion of Press Release
8 March 2016

Evers leans on dependability, service crew

Evers wouldn’t have been in position for a Sunday comeback without the reliability of his 250 ProXS (and the on-site Mercury service crew) on Saturday. Making the run back to the check-in point at the end of the day, Evers struck a log while on pad, severely damaging his propeller and causing a wicked vibration in his lower unit. Evers managed to continue motoring back to Wolf Creek in time to check in, and turned his boat over to Mercury’s on-site service crew for emergency repairs.
“That lower unit held together for 30 miles at 60 miles per hour,” Evers said. “The vibration from the damaged prop was just crazy – I was a nervous wreck, but I didn’t have any other choice but to keep going. I wouldn’t have had a chance to win the Classic without the durability of my 250 ProXS.”

Below is a photo we took of Mercury’s support truck while we were at the event.

Mercury Marine fishing tournament support trailer at Bassmaster Classic 2016 on Grand Lake.

Mercury Marine fishing tournament support trailer at Bassmaster Classic 2016 on Grand Lake.

As in our Day 2 photo below, we saw Mercury, Yamaha, Evinrude, and Suzuki outboards at the Classic. While not true in this particular photo, Mercury powered more boats than all the other manufacturers combined.

2016 Bassmaster Classic Day 2. Outboards at the dock before blastoff.

2016 Bassmaster Classic Day 2. Outboards at the dock before blastoff.

0 Categories : Bass Tournaments

Numerous previous posts concerned outboard motors striking submerged objects, breaking off, and flipping into boats, preventing or mitigating those accidents, log strike systems, accidents and legal trials involving such accidents and related topics.

We will now be covering this topic in this category of the PropellerSafety blog.

If anyone wonders why we are covering these accidents on, its because outboards that break off and enter the boat typically come in with the engine still running, the propeller at a high RPM, and often result in severe or fatal propeller injuries. Read More→

The boating industry has long been aware that marine drives can strike submerged or floating obstacles. In the early days they conducted on water log strike tests. In more recent times, some have moved to dry land impact tests (log strike test stands), and even considered virtual log strike tests (computer simulated log strike tests).

Old Mercury Outboard Log Strike Test

Old Mercury Outboard Log Strike Test

They moved from on-water testing to the dry-land impact testing shown below.

Log Strike Test

Mercury Marine Log Strike Test

As we understand it, the progression from on-water testing to dry-land impact testing was primarily verified by adjusting the dry-land impact masses to achieve similar failures to the on-water tests with the standardized logs at similar speeds. Dry-land impact facilities cannot be quickly dialed up to achieve a collision with a different kind of log, length of log, diameter or log, geometry of log, log submerged to a different depth, etc. The actual force X time profile may be quite different for a dry-land impact test than for an on-water log strike.

This progression (on water testing to test stands, to considering using simulations) was made without a total understanding of the science and mechanics behind log strikes.

We encourage Senior Design Projects, Sr. Thesis, Masters Thesis, Capstone, and Masters Degree projects on the science behind log strikes (the striking of driftwood, stumps, dredge pipes, and other floating or submerged obstacles by recreational boat outboards and stern drives). A better understanding of this science will allow more accurate designs and testing, resulting in safer boating. Read More→

0 Categories : Research Projects

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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The Storm Lake Iowa Laass v. Brunswick case has focused attention on outboard marine drives striking submerged objects and flying back up into the boat. In the Storm Lake accident, a ten year old boy, David Paul McFarlin was killed on May 31, 2010. A 175 HP Mercury outboard struck a submerged dredge pipe, flipped back up into the boat, and the boy was killed by its propeller.

First, a point of clarification. The U.S. Coast Guard does not recognize accidents in which people are on boats or otherwise not in the water when they are struck by propellers as propeller accidents, so this is “officially” not a propeller accident.

Marine drive manufacturers use relief valves and check valves in the trim systems of stern drives and larger outboards to cushion the blow and absorb the energy of striking submerged objects. The relief valves allow the cylinder rod to extend (drive to swing up as it dissipates energy), then the check valves allow the cylinder piston to settle back down to a “memory” piston. Mercury Marine is well known for conducting log strike tests which we discuss on our Laass v. Brunswick page, and supply an early video near the bottom of this page.

We often see U.S. Coast Guard Boating Accident Report Database (BARD) reports in which an outboard was torn from or broke off the transom. Some of these outboards sink, while others remain attached by cables, hoses, and/or fuel lines. In some portion of these instances, the outboard strikes a submerged object and actually flies up / flips up and lands in the boat. As a result, people in the boat can be struck by the outboard or cut by its still rotating propeller.

We decided to investigate BARD and some other sources to gain some greater understanding of these types of accidents and perhaps some insights into their frequency. Read More→