Harry,

I think I start to get your point, finally. Some explanation:

1/ I referred to the linear relationship between stiffness and resonant frequency, not to the linear nature of stiffness
2/ As far as increasing resonant frequency is concerned. Of course, it is obvious, that you can not increase the resonant frequency of the ROD beynd resonant frequency of the bare BLANK. All rodbuilder can do is to lower resonant frequency (and, as I presumed, stiffness). But this resonant frequency (and, as I presumed, stiffness) can me lowered more, or less.
If, for the same blank, I choose two different guide sets (as you did in your article "Weight vs. performance") the result will be resonant frequency X1, for the first set, and resonant frequency X2, for the second set. Now, when you say that in such scenario, the stiffnes of the ROD (not BLANK) will be the same for X1 and X2 - I've got some doubts. I always thought that added weight affect blank stiffnes somehow...

Finally, I would like to get to the point, which for me is the practical aspect of your article - what kind of blank rodbuilder should choose to get the most sensitive rod? I refere here especially to one of your previous comments about increase of stiffness towards the butt (which I described as a typical jigging blank construction)

Thank you for your kind interest in my enquiries :)

Best regards,
Pavel



Edited 2 time(s). Last edit at 03/01/2007 06:41PM by Pawel Tymendorf.

Pavel,
I think that I understand your question about weight affecting stiffness. I think the problem comes from thinking about stiffness as a number rather than as a curve. Adding enough weight that the rod is deflected does move the rod up the stiffness curve to a point on the curve that represents higher stiffness but the curve itself has not changed. So it is somewhat a question of definition. I suppose that you could say that this made the rod stiffer but I would not.

If I understand your second question, how do you get the most sensitive blank for a given fishing application I would say that you want the lighest blank in terms of power for the application, a blank with a slow action and a blank that is the lightest in weight for the power of the blank. I would also not forget the line either. Braided line results in much higher sensitivity than monofiliments.

The trouble with having the slow action, is that such a thing may not be what you want or need for the type fishing you're doing. Everything you do with regards to a rod involves some sort of compromise. Running out and suddenly switching everything over to slow action blanks isn't likely to result in the kind of super sensitivity that some might think. All these things need to be considered in light of a larger overall picture.

........

Tom,
I agree. Everything involves trade offs. For example, a slow action rod does not have the hook setting or fish handling power in the butt section that many types of fishing require. Sensitivity is a very important characteristic of the rods used in many fishing applications but it is only one of several important characteristics. Plus the gain in sensitivity from a relatively fast action rod to a relatively slower action rod is not going to be large. And the rods for some types of fishing require almost no sensitivity and other characteristics are much more important, heavy boat rods for example.

Emory – I too would like to commend you for your article and interaction in this forum. Couple of points – when you say the amount of energy required to move the tip of the rod (when comparing stiff vs soft) I think you’re actually referring to deflecting or bending the tip, as if the rod was clamped in a rod holder (or held tightly and still). This may lead to some of the confusion when mentally comparing the broomstick and the noodle rod because, at least in the case of the broomstick, one doesn’t think in terms of tip deflection but rod movement -- actual translation of the complete rod from one point to another, or at least a levering action with the fulcrum being somewhere near the fisherman’s hand or the rods balance point. This is more analogous to the point you made about the rod at a low fishing angle. Also, I think the fisherman’s grip may have a large impact on the perception of a strike. If the rod is held stiffly, then we’re looking for sensitivity via the deflection of the rod; in the case of a loosely held rod, then the fisherman may perceive whole rod movement, either laterally or by rotation about the point of grip. In fact, I would guess that the type of line, the way that the rod is held, and then rod properties affect the perception of a strike in that order. As somewhat of a sensitivity skeptic, I’d wager that, apart from the reduction of mass, a blanks inherent sensitivity might be relegated to the same ash heap as rod spine – i.e., interesting but not really useful. More cogitation required….

==dave Leonard==

David,
I agree with almost all of your points.
I agree that it is necessary to make any measurements that the rod is held relatively fixed at some point and the deflection is from the tip. If the whole rod is allowed to move then any measurements get extremely complex if not impossible. However, this is not the case with the calculations. The calculations do not assume that the rod is fixed or clamped at some point.
I also agree that the way that the rod is held can change how the rod acts in terms of what type of lever the rod acts like and how the rod is held can also affect how much damping the hand does to the vibrations or motion. And the angle that the rod is held also has a great deal of affect. I believe that the highest sensitivity is achieved when the rod is held so that it is basically parallel to the line and therefore the rod does not come into play or affect the sensitivity. The input from the fish goes directly through the line to the reel and the fisherman's hand and almost no energy is transferred through the guides to the rod.
I also agree that the type of line can have as much affect if not more than the rod itself on sensitivity. However, there is an additional variable when it comes to the line and that is the tension on the line. The more tension on the line the higher the amplitude of the vibrations. Or with a slack line the amplitude of the vibrations will be almost zero.
However, I do not agree that rod sensitivity is unimportant or can be put in the same category in terms of importance as the spine. I agree with you about the spine but I think that there can be a very large difference in sensitivity from one rod to another and that there are some types of fishing where the sensitivity of the rod is extremely important.

I would make the distinction here between the ideas of strike detection vs. the sensitivity of a rod or blank:

From a thread posted here last fall: [www.rodbuilding.org]

""Emory, I would make the distinction between rod sensitivity based on materials and design vs. the idea of strike detection. If you hold the rod so that the line is 90 degrees to the tip, you will maximize the effectiveness of the line to transmit a deflection to the rod. That means you need to change the rod angle depending on the location of the lure. Most people do this naturally, without even thinking about it. A rod held level if the lure is straight under as opposed to the tip held high if the lure is much further away, both tend to optimize the line to rod tip angle of 90 deg. The more you point directly at the lure, the more you depend on line properties and tension to transmit vibrations down to the hand. ""



I think there are a couple of things that are leading to confusion here on this idea of the sensitivity of a blank. One is that you need to define what you are measuring and make the distinction between vibrations transmitted down the blank, vs. translational motion at the hand. In the case of translational motion, the ideal case is a blank that is infinitely stiff with zero mass. In the case of a vibration transmitting down the rod, the amplitude of a pulse is a function of the mass and the stiffness. Now that's something even your Grandmother can understand.


From earlier in this thread:

"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 isn't quite true and can be a little misleading. Like modulus, the density is a material property, so it's more important to consider the specific case of the rod itself, which has a Mass. In the case of rod action vs. sensitivity. It would be possible to have a slow action rod that is less sensitive to vibrations than a comparable power fast action, simply because it has a lot more mass. Power for power, it is the difference in mass that makes a glass blank less sensitive to vibrations than a comparable carbon fiber rod. Similarly, given two rods of similar power and action, the lighter (mass not density) will be more sensitive. Conversely, you could also change from a high to a low density handle foam, but if you put a very large mass of the lower density foam on there, you'd decrease the sensitivity. Boiled down, given the stiffness you need for an application such as a blank, handle etc, it's key to reduce the mass when you want to maximize vibration transmission. This shouldn't come as a big surprise to anyone who's ever heard the term "lightweight and sensitive".


I wasn't following these threads very closely since I didn't have the article, but I've added comments to this earlier post since I was quoted from the discussion a couple weeks back over on the BFHP

[www.rodbuilding.org]

mark

Mark Gibson Wrote:
-------------------------------------------------------
> I would make the distinction here between the ideas of strike detection vs. the sensitivity of a
> rod or blank:

make the distinction between vibrations transmitted down the blank, vs. translational motion at the hand.
> In the case of translational motion, the ideal case is a blank that is infinitely stiff with zero
> mass. In the case of a vibration transmitting down the rod, the amplitude of a pulse is a
> function of the mass and the stiffness.
>

Very well put Mark- I think you have it exactly right.

To reiterate for those who might not read the whole thread,

D = F / K D is deflection distance, F is Force, and K is stiffness

As stiffness increases, deflection distance decreases (i.e. a stiff rod deflects/bends less). All deflection results in less movement of your hand. This demonstrates that the same force will move a hand holding a stiff rod more than a hand holding a soft rod.

I wish their were such a simple formula to refer to that would allow me to demonstrate that stiffer materials also transmit vibrations better...

Thanks Mike. Just to clarify the difference in the two types of motion though. The key here is that stiffness and mass resist motion.

For translational movement at the hand, the ideal case is infinite stiffness and zero mass. So stiffer rod will resist bending and produce a movement at the hand easier than something heavy and more flexible.

It's a little different for internal vibration motion, and the better case is low stiffness and lower mass. Again, you need to clearly define what you are measuring. The equation for the amplitude of a stress pulse through a tapered rod is a complex exponential, but the effect of mass and stiffness are clear. Also keep in mind that the frequency of the vibration will change with stiffness, so that will greatly alter the feel. And as Tom mentioned, the stiffness needs to fit the application, so the variable that you have most control over is the mass.

It could be argued that in the case of a big strike or tap, the translational movement of the rod at the hand will dominate and the "sensitivity" or vibration transmission is not as big a factor. As the taps or energy input becomes smaller and smaller, such as a so called light bite, the vibration component will play a bigger role. In either translational movement or vibrational motion through the rod, the key is to keep the mass as low as possible. Here's a good little reference book if you want to see some of the math: "Stress Waves in Solids by H. Kolsky" ISBN #0-486-61-098-5. it's only 9.95 in paperback.

There are a few ways you could set up and do the experiments. In the case of simply offsetting the tip, the rod will oscillate a number of cycles at its natural (not resonant) frequency and the amplitude will decay exponentially. This type of strain (offset) control experiment is a little different than what happens with the fishing rod, which is why I use the term stress pulse. In fishing the rod sees a force input, which is variable, not a constant deflection input.


mark

Mark Gibson Wrote:
-------------------------------------------------------

> It's a little different for internal vibration
> motion, and the better case is low stiffness and
> lower mass. Again, you need to clearly define
> what you are measuring. The equation for the
> amplitude of a stress pulse through a tapered rod
> is a complex exponential, but the effect of mass
> and stiffness are clear.

You have clearly given this a lot of thought. Could you clarify what you think about the relationship between stiffness and vibration transmission as it applies to fishing rods? Please ignore mass, as there is no debate regarding mass (we all agree mass kills vibration).

I do not think that there should be any difference of opinion on the effect of mass. The effect of the mass in a rod should be obvious because it has inertia and the inertia is directly proportional to the mass. So the higher the mass the more resistance to any movement, displacement, vibration or impulse, however you chose to look at it.
I think the difference of opinion centers around the effect of elasticity or stiffness. I did not make up the formula for mechanical impedance, the resistance to movement or displacement or vibrations, being the square root of the mass density times the elasticity. This formula is in your physics text book. I will agree that the formula is for a tube or a beam not for a structure that is more complex like a blank and is therefore somewhat simplified but this does not change the principals so I do not see how this added complexity bears on the discussion either. The formula also does not take into account the effect on mechanical impedance of rate of change or frequency but once again I do not see how this is bearing on the discussion at this point. It seems to me that what you are suggesting is that the formula for mechanical impedance is not correct. That the formula should be the square root of the mass density times one over the elasticity.

Mark,
I think that you should read the article. In it I explained the difference between longitudinal and transverse vibrations and the effect of the rod angle. I explained that if the rod is held so that it is parallel with the line so that almost none of the vibrations are being transferred through the guides to the rod that the rod has almost nothing to do with sensitivity. That at this low angle the vibrations are longitudinal and it is the characteristics of the line and the total mass of the rod and reel that determine sensitivity. But as the rod tip is increased the vibrations become more transverse and the characteristics of the rod now start to come into play and at 90 degrees they are almost all transverse and now the characteristics of the rod, mainly the mechanical impedance of the rod, are dominant in determining sensitivity.

Emory Harry Wrote:
-------------------------------------------------------

It seems to me that what you are suggesting is that
> the formula for mechanical impedance is not
> correct. That the formula should be the square
> root of the mass density times one over the
> elasticity.

Nice strawman! I'm not saying that at all. I'm arguing that mechanical impedance is beneficial to sensitivity. Mechanical impedance is a measure of how much a structure resists motion when subjected to force. It relates forces with velocities acting on something. And for our application, mechanical impedance is a desirable characteristic.

Mike,
That was not a simple straw man that was a scare crow.
You are suggesting that the amplitude of movement or vibrations will be transmitted through a rod at higher amplitude or with less attenuation if the rod is stiffer. This is contrary to the formula for mechanical impedance. Mechanical impedance is the resistance to the transmission of the movement or vibrations. I am suggesting that the higher the mechanical impedance the more that the movement or vibrations will be attenuated. In other words the stiffer the rod is the higher the mechanical impedance will be and the more the vibrations or movement will be attenuated and the lower their amplitude will be at the fisherman's hand and therefore the lower the sensitivity.

Please explain something to me. I am not an engineer or scientist, just a retired technician from the aerospace industry, and my terminology in this question may seem pretty simplistic, but here goes.

Since everything that we deal with is made up of molecules, I thought that density refered to number of molecules per unit volume of the material that we are dealing with. If that part is correct, then I relate the transmission of energy as being from molecule to molecule in a rod. I realize that it actually atom to atom, and suspect that most if it is done via the atoms valance electrons, but wasn't trying to get to the LCD.

I am making an analogy as if the molecules were in a straight line from tip to butt of the rod, for simplicity. I can see the conversion of energy from potential to kinetic in the first molecuse. It, in turn, bumping (for lack of more technical terms) into the next one in line and so on towards the butt of the rod. It would seem to me, that conservation of energy would come into play. I am of the opinion that energy/inertia would be slightly diminished on the second bump, again on the third and so on.

Am I out in left field, or would not the energy or inertia be diminishing relative to the number of molecules coming into play during this process?

Ask yourself- why are mass and elasticity on the same side of the mechanical impedance equation as multipliers???

It can only be because an increase of either one would have the same impact on mechanical impedance. Since we all agree that increases in mass decreases sensitivity, it must follow that increased elasticity (softness) decreases sensitivity as well.

Unless, as you say, that formula is incorrect

;-)



Edited 1 time(s). Last edit at 03/02/2007 01:04PM by Mike Naylor.

C. Royce Harrelson Wrote:
-------------------------------------------------------

> Am I out in left field, or would not the energy or
> inertia be diminishing relative to the number of
> molecules coming into play during this process?

The number of molecular interactions isn't as important as the mass of all the molecules relative to the stiffness of the matrix they form.

Would we not lose some of that energy upon each interaction?

C. Royce,
No, I do not think that you are not out in left field. I think that you are basically correct. The energy can be temporarily stored in a material in several forms but what you are referring to is the energy in the material stored in the speed of the electrons in the outer valance rings of the atoms. As the material absorbs energy the speed of the electrons increases and as the material releases energy the speed of the electrons slow. However, the electrons can only speed up or slow down in discreet amounts. When they speed up or slow down they jump from one energy level to another level, a higher level when absorbing energy or a lower level when releasing energy. The released energy is normally an electromagnetic radiation. The wavelength of the radiation is determined by the difference in the energy levels that the electrons jumped to or from. In the case discussed above it is in the form of heat.
Does that answer your question? If not someone who knows more about it than I do had better jump in to explain.

C. Royce Harrelson Wrote:
-------------------------------------------------------
> Would we not lose some of that energy upon each interaction?


Sure, but the question is how much energy is lost. And it differs between different types of materials.

Isn't one of the primary differences in the materials the difference in their mass density?

Emory, I understand your explanation. What I really was questioning (maybe not very clearly) was that since we cannot create energy, we are limited to the potential energy in the assembly, and if we start changing it to kinetic at or close to the rod tip wouldn't it also start a decaying process as it traversed, and wouldn't each interaction with other molecules add to the decay,and wouldn't a high density result in more interaction and more decay?