November 14, 2012

Give Me a Lever.....

It is purported that Archimedes once said "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world." Archimedes was likely speaking of a class I lever, that is, a lever in which the effort is applied on one side of the fulcrum and the resistance or load is on the other. Well, if Archimedes was a tenkara fisherman  he may have been talking about a class III lever. Tenkara rods, all fishing rods for that matter, are class III levers. He may have been alluding to a class III lever, but it would take a pretty long and strong rod to move the world! I'm not sure that even the famed Tenkara USA Amago could do that!



We as fly fishers use class III levers. Fly rods, of course, have different physical properties that can help us in our pursuit of catching and landing fish, but some of their properties need be explored to be fully understood. I am not a physicist, but I have some interest in the physics of rods since a spend as much time as I can using one.

Recently there have been some excellent articles on how to fight large fish with a tenkara rod. One article is from Discover Tenkara UK and the other is from Tenkara Guides LLC. I would encourage you to read these, if you haven't already. They are well written and enlightening. To these, I would like to add my own analysis.

Although tenkara rods are somewhat different than western fly rods, they have many of the same characteristics when it comes to fighting large fish. In this post I'd like to examine the forces exerted on the fish and how those change with just varying the angle of the rod to the fish.

We pride ourselves, in tenkara, in being able to use a light tippet, sometimes lighter than we would have used when fishing a western setup, because the tenkara rod does so well at protecting the tippet from breakage. How is this so? Because the tenkara rod has a much more flexible tip than does a western rod. Well, for the most part, tenkara rods themselves are much more flexible not just their tips. But what happens when you have a really flexible rod and you hook a large fish? Lets examine the forces applied to a fish when using the rod at different angles. 

Rod angle to fish (Adapted from Borger Presentation)


 Years ago I bought Presentation by Gary Borger. It is my favorite "manual" on fly fishing. In there Borger reviews fly rod dynamics like this: look at the diagram above. When holding the rod sharply upright, like nearly 90 degrees or so (A), the tip of the rod is maximally bent and there is very little force applied to the tippet and to the fish. Only the flexible tip section of the rod is bent. Yet, by decreasing the angle the rod dynamics change. Decreasing the rod angle (B) will bring into play the more stiff mid-segments of the rod and thus greater force is applied to the fish -- and the tippet! If you continue to lower the rod, approaching 45 degrees (C), the stiffest segment, near the butt, will begin to bend and take the load. This is when you have the most force applied to the fish. This is also when your tippet is the least protected!

Here is a real life example. I used my Tenkara USA Iwana 12 foot attached to a 6 pound weight with a level line to show the differing forces applied when the rod angle is changed. Here, in the first image is the force applied on the "fish" when the rod angle is 90 degrees. No matter how much I tried I could not get above 0.265 kg pull load at 90 degrees. The top 1/3 of the rod was bent, but the mid and lower sections were relatively unaffected.

90 degrees maximum pull: 0.265 kg


Next, I lowered the rod to approximate a 65 degree angle. Again, I tried multiple times to move the weight but I never could get above 0.340 kg load. The rod was bent well into the mid-section.

65 degree maximum pull: 0.340 kg

Finally, I lowered to rod to about 45 degrees. Again, pulling the weight as much as I could I got a 0.620 kg pull load. The rod was bent all the way to the handle.

45 degree maximum pull: 0.620 kg (see the attached tippet?)


See how the pull force goes up as the rod angle is lowered! It doesn't seem like much, but when you apply it to a live, dynamically moving fish in water that little change in pull load adds up to real fish-fighting force!

Worried about breaking your rod with the added force? Sure, we all do. So, use the right rod for the job and use the right fish-fighting mechanics. How do rods break -- at least western rods? Go to Youtube and watch Tim Rajeff explain rod dynamics.

Tenkara, however, has a challenge when it comes to changing the rod angle. Since we have a fixed line, when compared to the western rod and reel, to change the angle of the rod you have to allow the fish to move further out or bring it closer in. This may be a problem if the fish is really large and wants to run. This is where side pressure comes into play.

 As the fish runs away from you, that is, away from the point of resistance, you naturally begin to lower the rod -- that fixed tenkara line makes you do it. However, if you lower the rod too far you begin to greatly increase to forces on your tippet. At some point the rod may no longer be able to protect the tippet and it will pop. In this instance move the rod quickly to one side (generally the side that will bring the fish around the quickest) and begin to pull the fish's head around. When the rod is held horizontally it applies significantly more pressure on the fish than when held vertically. This is well described in the Discover Tenkara UK article. Please note that with the rod held vertically you are fighting the weight of the fish and the water above it. All the fish has to do is lower its head and the force of the water pushes it down making it feel heavier. It's like trying to lift a deadman stake out of sand. When you put side pressure on the fish, it has to fight against the pull of the rod the whole time without help from the water column's weight. It is thrown off balance and tires more quickly, thus it is easier to bring under your control!

In review, we, as tenkara fishers, are like Archimedes: give us a lever and a place to stand and we will (try) to move the world -- or at least that big brown that haunts our dreams! We prefer beautifully made class III levers rather than a rigid pole, like Archimedes uses, but that is one of the wonderful challenges of tenkara -- how to land that big fish on a fixed line!!

I for one will continue my experiments in real-life physics by going fishing whenever and wherever I can!! Please join me!








4 comments:

  1. Tom, I have a hard time understanding how this statement could be true if you were fighting a fish that was pulling rather than a weight that was stationary: "The top 1/3 of the rod was bent, but the mid and lower sections were relatively unaffected." If the fish continued to pull, I believe (I know from experience) the bend would travel down the rod and continue to do so until either the tippet or the rod broke or the fish tired.

    Repeat the experiment while walking backwards (or some way moving the weight away from you) with the rod held at the appropriate angles. If you used the same tippet on all three experiments, either the tippet would have broken all three times, or the weight would have moved all three times, or you would have broken at least one or two rods - maybe all three depending on tippet strength. Bottom line, if neither your rod nor your tippet broke, you didn't apply maximum pressure. The point of the excercise should be to see what tippet strength is "safe to use" for a given rod at each angle.

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    1. Yes, I see your view. But the actual point of the exercise was to show the change in pull force as the rod angle changes. As you pointed out, this example uses a static "fish", but when fighting a live fish the rod angle would be changing constantly, either by large amounts as when the fish runs or smaller amounts as when the user continues to apply pressure and the rod bends. My point was not to try to show the amount of pull force needed to break a given strength of tippet or rod, only to show the the pull force does change as the rod angle changes. You said "The point of the excercise should be to see what tippet strength is "safe to use" for a given rod at each angle." That would be an interesting exercise for sure!

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  2. Guess this experiment shows what happens when i tenkara fish from my kayak.
    As the fish pulls and the yak moves accordingly the effect is (almost) the same as to fight a static fish.

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    1. I think so. It's probably all relative!

      -Tom

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