I've read (several times) Emory Harry's excellent article on SENSITIVITY in RodMaker magazine and thought it was very educational.

He stated in the article that:

"So the higher the mass density of the blank and/or the higher the stiffness of a blank, the higher the impedance to vibrations will be and the lower the sensitivity. And the lower the mass density and/or the lower the stiffness of a blank the lower the impedance to vibrations will be and the higher the sensitivity will be."

This is somewhat of a revelation to me since I've always been of the belief that a stiffer rod was more sensitive because it would not absorb vibrations like a softer rod.

Am I correct in thinking that a higher modulus blank material would be more sensitive since less material would be required to achieve the same stiffness, resulting in less mass density?

In a nutshell, yes. A lower mass density will, under most circumstances, improve the sensitivity of the rod.

We don't want to say that a softer rod "absorbs" vibrations because that really isn't the case. A softer rod, given the same input, will "move" further and therefore create more of what is felt in terms of what we call sensitivity. The "absorption" of vibrations, or perhaps what you might call the damping factor, isn't much, if any, of a factor in something the length of a fishing rod.

............

Jim,
You have it right. The more mass that the rod has and the stiffer it is the higher that the mechanical impedance, the resistance to vibrations or movement, will be and the poorer the sensitivity will be.

I am not exactly sure what you mean by softer but if I understand you are right there as well. A rod with a slower action (lower action angle) will have better sensitivity than one of the same power with a faster action (higher action angle).

Also the mechanical impedance increases with the frequency or speed of the input to the rod up to the rods resonant frequency and beyond the resonant frequency. But the mechanical impedance drops dramatically at the rods resonant frequency. What this says is that almost everything that you feel will be at a very low frequency or at the resonant frequency of the rod. In other words, any input that is faster or higher in frequency than the resonant frequency of the rod will be highly attenuated.

Tom is also right about the damping factor. The velocity of any vibration through the rod is so high that it reaches the fisherman's hand long before the damping factor (how quickly the rod damps out vibrations) has had time to damp out any significant part of the vibrations.

By the way there is an error in the article that no one has yet noticed and I apologize for. The velocity of the vibrations in graphite is 10 to 20 times as high as the velocity in air. The velocity in air is on the order of 1000 feet per second. The velocity in carbon fiber is 10,000 to 20,000 feet per second.

So a spaghetti noodle would make for an awesomely sensitive rod due to the very very low stiffness???

A softer rod moves further at it's tip, that is true. But given the same input it does this at the cost of less movement at the butt of the rod. It's simple physics.

I will not believe that given two rods of equal mass, the softer rod will be the more sensitive (e.g. result in more felt vibration in the hand).

Thanks guys for the additional input.

I should probably clarify that I was mistaken in thinking that a stiffer rod was more sensitive. I usually cut several inches off a “fast” tip blank because I feel it gives me better control of a bait. Although this may come at the expense of casting ease, I feel it removes the “shock absorber” effect when I twitch a topwater lure, rip the lure through weeds or set the hook on a fish. I’ve always thought of a fast tip as you would shocks on a vehicle that make the “ride” more comfortable and eliminate the “bumps” (I want to feel the "bumps"). I’ll admit the error of my ways in thinking that the stiffer tip was more sensitive, although I’ll probably still be willing to sacrifice some sensitivity for the lure control.

Remember, there is more than one factor at work here. A spaghetti noodle falls short on many counts.

.............

Mike,
You are right it is simple physics. A spaghetti noodle, one that been cooked, has no elasticity. The transmission of vibrations being mainly a function of the mechanical impedance (mass density and elasticity) is only true for elastic materials.
I have not thought it through but I think that the transmission of vibrations through a spaghetti noodle is going to be mainly a function of the mass per unit of length and the tension on the noodle much like the case with a braided line.
Think about it like this. The stiffer a rod is the more force that it will take to move the tip a given amount and the more mass it has the more force it will take to move the tip a given amount. And the less increase in mass and the less increase in stiffness from the tip to the butt the more of that vibration will get from the tip to the butt ......with an elastic material.
If you are still not convinced send me an e-mail and I will give you some reference sources that you can look up on the INTERNET that should convince you.

I think that some kind of testing would go a long way towards convincing the skeptics that the science is applied correctly to replicate the relative sensitivity of various rod configurations.

Jim,
That is what Tom keeps telling me.

Emory,
If you pursue this, I wouldn't use cooked noodles.

Wrapping wet noodles would be a real problem too, you would need a LOT of rod supports...

Seriously, my point is that without stiffness there is -no- vibration transmission. As stiffness increases, so will transmission- to a point. At some level of stiffness you prevent vibration, sure. I suspect this level is way above any normal rod.

But is "vibration" really what you feel when fishing? I don't think so. A fish @#$%& in a lure creates a lateral movement of line. This lateral movement, dampened by water and line stretch, moves the rod toward the fish. I feel a take primarily as a tightening of my line or a subtle tug, not a vibration. The rod isn't "vibrating," just moving. And a soft rod will move your rod hand less than a stiff rod (length and mass being equal).

Mike,

I hope that I’m wrong about admitting that I’ve been wrong. I’m inclined to agree with your logic, but I know that sometimes if you do (or believe) something “wrong” long enough, it becomes “right”.

I have a lot of respect for Tom and Emory’s knowledge, but it’s hard for me to let go of my shock absorber theory. (I’ve believed it for a long time) It seems to me that if you applied one once of force to a flexible tip, the tip would easily deflect , “absorbing” the energy. Whereas, if you applied the same amount of force to an extremely stiff tip, there would be little or no flexing and the entire rod would be deflected.

Until I can jury rig a test setup to validate what Tom and Emory is saying, I’m going to assume they’re correct and my logic is flawed.

Btw…I know you didn’t mean a cooked noodle.

Mike,
You must not subscribe to RodMaker. In the article I defined sensitivity as how much of the input energy results in movement or displacement or vibrations at the fisherman's hand. I also suggested that a fish's bite can come in a number of forms like a tug or pull or even a release of tension on the line as you suggest or it can be a vibration. I only used the term vibration for purposes of simplification.

I agree with you about stiffness. Modulus of elasticity is the property of a material that translates into stiffness in a structure like a rod blank. Again, the transmission of vibrations, or displacement or movement if you prefer, is primarily a function of the mechanical impedance and the mechanical impedance is a function of the elasticity (stiffness) and the mass density. It is actually the square root of the elasticity times the mass density. But this is only true for materials that have elasticity. Naturally we are mainly interested in the materials that rods are made of like carbon fiber and fiberglass that have elasticity and structures that have stiffness like a rod blank. Your wet noodle does not have stiffness or at least it has very little. As I mentioned earlier I think that a better model for your wet noodle is the model used for line which is the mass per unit of length and the tension on the line or in your case the noodle.

It was also stated in the article that the vibrations or displacement come in two forms or a combination of the two. If the rod is held at a very low angle relative to the water the vibrations or displacement will be mainly longitudinal, you used the term lateral movement which is fine, but as the tip of the rod is raised they will become primarily transverse. When the displacement or vibration is primarily longitudinal the characteristics of the rod have almost no effect on sensitivity. Sensitivity will be determined primarily by the line, which I think is what you are suggesting. However, as the vibrations or displacement becomes primarily transverse then the characteristics of the rod come into play in determining sensitivity.

If you are interested in this you should get a copy of RodMaker magazine and read the article. Plus there will be at least one and maybe two follow on articles to this one on sensitivity in the future issues of RodMaker.

If on nothing else we sure agree on the difficulty in wrapping that wet noodle.

Jim,
The rod does not absorb the energy. It either has to transmit it up the rod or dissipate it in heat which is what your shock absorber does. But the dissipation of the energy into heat takes time. That is what the damping factor is. When you deflect a rod and release it and the vibrations get smaller and smaller over time it is because the kinetic energy is being converted to heat. But the vibrations or the displacement is transmitted up the rod several orders of magnitude faster than that. The damping factor damps out the vibrations slowly at the rods resonant frequency which will be on the order of two or three or four cycles per second. But the vibrations travel up the rod to the fisherman at 10 or 20 thousand feet per second.

Maybe this will help. It takes more force to deflect a stiff rod say one inch then it takes to deflect a less stiff rod one inch just as it will take more force to deflect a higher mass rod one inch than deflect a lower mass rod one inch. Therefore for a given applied force at the tip of both rods there will be more displacement or higher amplitude vibrations transmitted to the fisherman's hand with the less stiff rod or the lower mass rod.

Harry,

don't have this RM issue yet, and can't wait to read your article. It seems to me, that it is a kind of a revolutionary discover, completely opposite of what many of fisherman and rodbuilders thought so far about red sensitivity.

From your past articles, I came to a conclusion that the rod performance is the best, when the resonant frequency is higher. In the article "Rod versus performance" (RM Volume 8, Issue 3) you stated: " The higher the resonant frequency the better the sensivity and feel will be".

This seemed to go along with what the blanks producers offer this days. Blanks for the "feel" applications, especially jigging, are generally "extra-fast action" blanks, which means they are blank with high-action-angle. Rather stiff, with high resonant frequency (correct me if I am wrong, but I presume that for the majority of the blanks stiffness goes together with resonant frequency)

Now, what I understood from the current discussion above is, that this way of thinking..... is no longer valid? Frankly speaking I am very, very confused with what I am reading now. It will be a fundamental change in the way of thinking indeed to get now that low-action-angle (preasumtion: lower resonant frequency ) blanks, actually give better sensitivity. If I made a mistake somewhere Harry, hope you will correct me and explain some things in simple terms :) The practical cosequences would be the most interesting for me - what kind of blanks we should look for for the maximum sesitivity.


Best regards,
Pavel



Edited 1 time(s). Last edit at 03/01/2007 03:05AM by Pawel Tymendorf.

Emory-Tom could confirm that I've been a subscriber for a long time. But I've been a scientist, fisherman, and rod builder even longer. You seem to be a scientist as well, I suspect you realize that you never addressed my main point. A soft rod will move your rod hand less than a stiff rod (length and mass being equal), and movement of the rod at the point of your hand matters most in detecting the bite of a fish. Resonance frequency and vibration orientation sounds scientific, but I think it's a red herring.

It's a very tough thing to test, really. You would need to run a line from the tip of a rod out some distance. Than you would want a sensor near where the grip would be. Then you would move the line or tap it, and see how much the rod moved at the grip. Would be a royal pain to standardize and calibrate..

I say all this respectfully, as just my opinion. It's fun to think about, and I'm very thankful that people like you are taking the time to write and get everyone thinking about this. It will make us all better builders.

I think what we’re dealing with here is a “reverse engineering” situation. Sensitivity or “feel” (or any other rod attribute) can and probably should be looked at as the final “product”. How we get there can be hypothesized to death, but you can only do so much “engineering” and then you need to build a prototype to prove out the theories through trial and error (comprehensive testing). There is certainly no lack of “prototype” rods that could be tested to get conclusive results. Although I’m beginning to suspect that some of the results may not be as conclusive as we’d like. Undoubtedly, computerized test equipment may show us significant values, but what we actually “feel” may be much more subtle and less discernable, unless the blanks tested had significant differences in configuration (very fast vs. very slow) I suppose that there would be psychological advantages of knowing that our equipment is designed to give us the ultimate in performance. It should be noted that “sensitivity” is only one of several attributes that we look for in a rod and that sometimes to get more of one we have to give up on another.

It seems to me that it wouldn’t be too hard to come up with a test to compare relative sensitivity for “stiff” vs. “soft” rods. It could be similar to a hearing test, except the “subject fisherman” would be asked to signal when he FEELS a signal. If he (or she) was blindfolded and not aware whether he held the "stiff" or "soft" rod and a series of “controlled” taps or bumps would be applied at the end of 30 feet of line (mono and braid could be part of the test), the responses could be recorded and averaged to prove the science was correctly applied.

Could someone tell me what causes this feel.

1. You are holding a rod fishing with a jig head and plastic bait with monofilament line on a medium action rod fishing in 12 feet of water with about 50 feet of line out.

2. You feel a heavy thud solid and only one big slam in you hand and basically nothing else no line movement to speak of of the line - it kinda goes limp and you set the hook.

3. What you find when the fish is boated that it will normally be a large fish and the jig head will be stuck way down in the throat in the gill plate.

4. It is evident that the fish flared its gills and sucked the bait into the throat under high speed. The jug head hit the gill plate at velocity.

How can this get transmitted back to the hand. Are you really feeling the "stop" of the bait and which rod characteristics will transmit this the best?

Bill,
Your question about “which rod characteristics transmits this the best?” is a profound one. Many of us who thought we knew are now in doubt.
Your scenario is one of many where “sensitivity” is an issue. I recall years ago seeing a video of a bass inhaling a crankbait and expelling it seconds later. When the photographer/diver asked why the fisherman didn’t set the hook, the guy replied “I didn’t feel anything”. If his rod was more sensitive, he would have literally felt “nothing”as opposed to the swimming of the bait.
I think many of us are now very interested in the answer to your question.