The Leash

[Nova Kaw 650]

I have serious doubts about the failure mode that most are assuming. If a boat running a 30 MPH or greater strikes an object with the lower unit hard enough to destroy the transom or the motor mounts, how does the motor get into the boat? Is it going to flip about the axis of the destroyed connection point and fall into the boat? I wouldn't think so, it would just fall off or hang by the other equipment on it while the boat continues to move forward. I have always thought the problem arose from the motor rapidly detaching from the boat while still running and the prop still generating significant forward force, thus throwing the motor back into the boat violently. If that is true, the steering cables are not necessarily strong enough to stop its momentum, they are just long enough that the motor has stopped moving forward before they broke since the prop is no longer in the water.

Not saying this is true, I just can't see another way for the motor to actually get into the boat. If this is the failure mode, the tether might actually make it worse by keeping the prop in the proper location to drive the free motor forward.

There might be a case of a motor driving into the boat, but as a person that destroyed two LU's over the past 10 years, and did the neck swivel in time to see the engine try to flip into the boat, I believe this is the more likely scenario.

[1bluemcm]

This whole website is interesting, this particular page has a lot about motors hitting things and flipping into the boat, even mentions the Leash. There are other pages that discuss this, they have compiled real world examples of it happening, several with fatalities. Interesting reading if you are into the granular details.

http://www.propellersafety.com/prope...board-flipped/

[PGIC]

[PGIC]

I had trouble getting this text attached to the chart image above, so attaching via separate message.

There are two basic modes (ways) in which a large outboard motor can enter a bass boat that struck a floating/submerged object.

First a little background information. Large outboards use hydraulic relief valves to absorb the energy of impact as the drive rotates upward. Most manufacturers of large outboard motors conduct some sort of log strike durability testing. They want their outboard motors to be able to survive an impact with a floating log. Each manufacturer has their own test procedure. Those tests are now often simulated on a test stand of some sort. Typically the outboard motor will strike the test object, rotate up to near maximum rotation, and then swing back down in a successful test.

For the first mode of failure imagine an outboard manufacturer that designs for an impact with a ten foot long, 12 inch diameter log, of a specific type of tree, water soaked to float right at the surface. This manufacturer elects to test at 37 mph. They design some text fixture / procedure to replicate that load or to replicate the failures caused by such an impact during on water testing. They improve their new outboard designs till they consistently pass their test. But what happens if you hit a little bit larger log at 37 mph or you hit a log equivalent to the one they test with, but you hit it a 40mph. In either instance you run the risk of the outboard motor exceeding its maximum rotation. Basically the outboard motor rotates all the way up, then breaks off and continues to rotates over into the boat. The outboard typically first crushes its cowl against the rear deck, then goes all over the place.

For the second mode of failure, imagine striking a log equivalent to the one the outboard manufacturer designs for, but you strike it at 50 plus mph OR imagine striking more a more solid object (stump, dredge pipe, rock, or submerged part of a bridge) at 35 mph. Whether these are the exact speeds or impact items or not, eventually you reach a point where the outboard motor can not rotate up fast enough to allow the boat to go over the object. You begin to have the full mass of the boat trying to barrel on over the object but the outboard motor is holding the boat back. The outboard cannot clear the object fast enough. In these instances the outboard can break off at the bottom, meaning it breaks off before it begins to swing up or at least before it clears the object.

We drew a chart showing these two modes based on what what struck and how fast the boat was going. The yellow band in the upper right represents the area in which the outboard has rotated all the way up and everything begins to stretch to the limits before something breaks. a few impacts will be in that zone. You are saved by the extra give in the transom, in the mounts attaching the motor to the swivel bracket, and in the stretching of the jack plate.

The peach area in the top right represents the instances in which the outboard motor over rotated into the boat. (the first mode)

The lavender area in the very top right of the chart represents the instances in which a more solid object was struck or the boat was going considerably faster than the manufacturer's log strike test speed. In these instances the outboard motor breaks off shortly after impact, long before it cleared the object. It rotates on up and the boat rapidly slows due to losing its propulsion force. The boat noses over into the water loosing its trim and rapidly slows. The outboard motor still rotating in the air overtakes the slowing boat. The cables and controls begin to retard the outboard power head on its starboard side causing the outboard lower leg to swing to port and the propeller to come down in the area of a bass boat passenger's head.

gary

[MN1965]

OK. I see that the diagram is labeled "rough draft", but the curves and relative size (frequency) of the shapes are absolutely meaningless without scale. What the heck is "large log" or "maximum speed"? If not drawn to scale with the impact velocity, the resistance of the object and the structure of the engine mount taken into account, it is silly.

[skeeterator]

Sob, some of you guys are waaaaay over thinking a simple device.

[MN1965]

Sob, some of you guys are waaaaay over thinking a simple device.

I'll admit, I'm among those who is probably more worked up about this than I should be. After all, no one is forcing us to buy it. My frustration stems from the marketing. They are taking a very rare (but complex) problem and proposing an expensive (but untested) solution by preying on fear instead of facts. My guess is that if it were a significant issue with a simple solution, every outboard manufacturer would be shipping their engines with something similar to protect themselves from liability.

[PGIC]

... the curves and relative size (frequency) of the shapes are absolutely meaningless without scale. What the heck is "large log" or "maximum speed"? If not drawn to scale with the impact velocity, the resistance of the object and the structure of the engine mount taken into account, it is silly.

You are certainly entitled to your opinion.

I propose the colored areas represent an overview of the different ways a log strike system can respond, and how it can fail.
AND that the information conveyed by the chart helps better understand existing outboard motor flipped into the boat accidents, and how to prevent them in the future.

Areas to the left or below the blue area represent modes in which the log strike system is not activated (the outboard does not start swinging up because the boat has enough energy to push the debris out of the way OR the boat does not have enough energy to cause the relief valves to open when the object is struck). In the latter instance, the boat just stops with the outboard leg against the debris.

The large blue area represents the region in which the log strike system is triggered and allows the outboard to swing up over the object, then swing back down. The log strike system and outboard function in the manner they were designed. They do not fail.

As mentioned above, the yellow ribbon area is where everything is stretched a bit just before something breaks. The peach area is where the outboard over rotates, and the lavender area is where the outboard breaks off before it clears the object.

While it is a Draft, I propose the shapes of those areas with respect to each other is representative of their typical shapes in real life for a specific outboard and boat.

For example, the "X" in the blue area marks a manufacturer's log strike test speed and the relative size of log they choose to test with. The colored areas make it easy to see that if you speed up a bit your will the be in the yellow area, and if you speed up a little more than the manufacturer's test speed, you would be over rotating the outboard and it would break off. Similarly looking at the "X" test point, if you increased log size a bit beyond the one used by the manufacturer the outboard could over rotate into the boat.

Personally, I find the graphic showing these various modes and how they related to each other, how they relate to increasing object size / increasing solidness of objects, and how they relate to increasing speeds quite helpful.

Among the interesting points is that an outboard can break off and enter the boat at slower than the manufacturers log strike test speeds if you strike a more solid object.

While it would be interesting to develop an exact chart for one specific boat and outboard by crashing countless sets of them into various floating/submerged objects at various speeds, I personally see the value in the general knowledge of the outcomes without spending millions of dollars on testing.

From an engineering perspective it is much better to have a qualitative understanding of what is happening than no understanding at all. The colored areas provide a qualitative understanding of how the drive will behave and may fail as the speeds increase and the objects struck become more challenging to the log strike system.

While you may have a comfortable understanding of what goes on and how large outboard motors can break off and enter boats, at least one major outboard manufacture relatively recently testified in a legal case they were unaware this had EVER happened before.

If they told the truth, the qualitative colored chart could have enlightened them to some challenges faced by their outboards.

Thanks for your comment.

gary

[leethefishking]

No way that sea dog one holds an outboard. That cheap carabiner would snap under the first 50 pounds of pressure.

[MN1965]

No way that sea dog one holds an outboard. That cheap carabiner would snap under the first 50 pounds of pressure.

I don't think the Sea Dog product is even intended to be used in the way we are discussing. I think that is like the old chains that were mounted in small boat transoms that snapped into a hole in portable outboard mounts. It was just to allow you to recover the motor if the clamps came loose and it went over.

[Chisco]

No way that sea dog one holds an outboard. That cheap carabiner would snap under the first 50 pounds of pressure.

Probably true but that may be enough to keep the motor from coming over and allow the motor to fall overboard. I would think the mid section of the motor is going to break in half with any type of unbreakable tether wrapped around it and may even cause it to shatter into many pieces. Maybe a "bra-type" harness around the mid section can expand the stress point. Regardless, without proper testing, everything else is speculation.

[Chisco]

Whatever happened to Scott Bird? After saying he would answer any question, he ran for the hills when the tough questions started.

Edit: Corey, from The Leash, clarified that Scott Bird is simply an independent dealer of the product and not part of the company. That may be why he hasnt answered any of the questions posed.