I tried to wrap my noodle around resonant frequency applied to building more sensitive rods several months ago and it drove me kind of nuts.
I'm Ok now, fileing guide feet, winding thread, fiddling with epoxy, and reading the forums.
The last thing I was reading about when trying to grasp the relevance of resonant frequency to sensitivity was an article on the RF of the human hand and how it changes depending on your grip. That leads me to speculate that rod balance may be a major facter in how much the angler is able to feel the slightest bump.
Any thoughts regarding resonant frequency of the anglers hand with a firm grip vs relaxed grip?
I'm wondering if the new sensitivity article is going to touch any more on rod balance or spin vs casting?



Edited 1 time(s). Last edit at 12/11/2007 09:04PM by Bill Peifer.

Balance is a tricky issue. To achieve it, you sometimes have to add weight to the butt, which in and of itself tends to undermine sensitivity. I do know some bass anglers who feel that a tip heavy rod helps you better detect the bite. I tend to disagree but have no scientific test data to back up my own belief on that particular matter.

By the same token you have to also factor in the fisherman's alertness, which can be worn down over a few hours by fishing with an out of balance rod. The whole problem with the issue of sensitivity is that it encompasses so many factors in so many ways that it's hard to design tests that will provide across the board data.

I try to build the lightest rod possible. I don't worry too much about balance personally, because by keeping weight off the top half of the rod I don't have rods that tend to be very tip heavy, if at all. Obviously this becomes more and more difficult as you deal with longer and longer rods. Still, for me, the lightest possible overall configuration has been the most comfortable and in purely subjective terms, is the most sensitive for me. The easier it is for the fish to move the mass I'm holding, the more sensitive the rod seems to be.

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

The RF is just mysterious to me, I can't quite figure.
When I do need hightened sensitivity I reach for spinning tackle. My finger is on the line and the reel helps hold the tip up as I watch the line for a strike.
You would think that technique negates the need for a sensitive rod. A long time ago when I switched from bait to artificials for bass, I told the guy at a rod shop that I wanted to learn how to fish rubber worms. He sold me a spinning rod and I picked right up on the technique. Had a blast. After I broke that rod my success rate with worms went way down. I can't help but think it was due to lost sensitivity.

There have been a number of things written about sensitivity, RF, and other similar topics over a lot of years. Some of these have been centered on modulus, some on weight and/or balance, some on length, and other stuff too. One of the common threads, though, has been that each of these discussions seems to miss one salient point about rods that's a focal point of a related product - golf club shafts.

A lot of effort is spent on golf club shaft design, to maximize the effect of displacement and recovery during the swing. A lot of that design work goes into making certain of the points on the shaft where the delta of the bend is strongest to provide the quickest recovery. There are more than one of these points, each with a specific effect on the overall "action". The management of these factors through the design process is what makes a shaft suitable for a senior player, or a stronger pro with a much faster and stronger swing.

As I understand it, RF is basically the measurement of the time it takes for the shaft - or rod - to recover from a displacement action. It starts with the shaft at rest. A force is applied at some point along the shaft - or rod - it could be from one end or the other, or in the middle for that matter. The natural tendency of the rod is to return to it's original position at rest. How long it takes to do that is the frequency part. How much the rod over-compensates for the applied force is the resonance part. Or maybe it's the other way round - I'm sure one of y'all will know. In any case, eventually the rod returns to its resting state. The number and delta of each recovery cycle constitutes the RF. No, it doesn't just return to rest on the first recovery movement. It resonates - sort of like the physical properties of sound waves following a note on an instrument. Yes, each recovery cycle is exponentially smaller in time and distance from rest. Think about "snapping" a rod in a store to see how the tip moves. That movement doesn't come back to center without first going past center, maybe several times.

Will shorter rods recover more quickly? Not necessarily - depends on the taper, wall thickness, exact mix and placement of materials along the rod, etc. Can the way you lay up your guides affect the recovery cycle? Absolutely.

So after all that, So What? Well, the shorter the recovery time, the more sensitive the rod is. Notice I didn't say anything about stiffness - even a stiff rod exhibits the same physical properties. I also didn't say anything about torque. For purposes of this little note, that's just another factor in the recovery-to- rest time. BTW, two rods the same exact model will have different RF numbers.

As for how it feels in your hand, that's between you and your hand. Ultimately, although sensititivity is quantifiable (just like loudness iof a noise), it's subjective.

Just some thoughts. I know a lot of you will tell me I'm wrong, but that's OK - when you're done with me, I'll know more than I do now. So, have at it.

Uncle Russ
Calico Creek Rods



Edited 1 time(s). Last edit at 12/11/2007 11:41PM by Russ Pollack.

I often hear golf shafts and fishing rods discussed as if they were performing a similar function. I don't think that anything that a fishing rod will ever do is even remotely similar to the act of a swinging golf club striking a stationary hard ball. The energy/motion of a fishing rod being cast has no resemblence to that of a swinging golf club. IMO, the only thing they have in common is that they are both made of graphite (as are flag poles) Not trying to open up a can of worms, and I could very well be wrong, but I just don't see anything in common.

Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!

I’m pretty much in agreement with what Tom posted.

While adding weight to balance a rod may take away from its sensitivity, it adds to its bite detection.

Example;
If your rod is tip heavy; its natural tendency is to pull down towards the water and fish.
If a fish lightly picks up you bait just slightly moving off (which often happens while bass fishing in structure) you will not feel the bite as well because your rods tip is trying to go the direction of the fish anyway. The only thing stopping it are the restraints being put on it by your hand and wrist.

If you rod is tip light; its natural tendency is float up and away from the fish and water.
Now, “If a fish lightly picks up you bait just slightly moving off” it stops dead the rods tendency to float up and revises the direction.

This action in itself increases your awareness that something is happening at the end of you line “Increased bit detection”

Also a rod that is tip light allows your hand to be in a more relaxed state while fishing allowing for increased sensitivity and comfort simple because you are not fighting the weight of the rods tip to keep it up out of the water

Wow, that's something I had never thought about. I can see the sense behind it. If I had known it was this hard to catch a fish I might have taken up a different hobby!

If it weren't this hard to catch fish were would the challenge be, at least with bass fishing, ( I can go bream fishing and catch one one every cast with a coat hanger, a little line, hook and some earth worms.) But I don't find a challenge in that only dinner



Edited 1 time(s). Last edit at 12/12/2007 02:49PM by Steve Gardner.

Resonant frequency has a major impact on how a rod performs and how it feels. Trying to understand how it impacts, and engineer those desired qualities into a rod gets really difficult.
Everything has a resonant frequency. Russ, it is not the measurement of time it takes to recover from a displacement action. That would be measuring the decay rate of the amplitude of the resonant frequency.
The main effect on resonant frequency are rod length, stifness and weight. Change any one of those and you change the RF.

Having said that, generally the frequency increases as the weight decrease, stifness increases and length increases. If you look at a simple harmonic wave, starting at zero, it rises to the crest (how high is amplitude) falls to zero, continues to the trough and back to zero. The resonant frequency is the measurment of how many times per second it does this. Every time it crosses through zero, there is basically no displacement. You can see this when you hold a rod in your hand and wiggle it back and foth, a couple of spots will appear not to move.

If you have your hand on the rod where the zero point of the resonant frequency is, you will feel very litlle vibration transfer. If it is held at the crest of the resonant frequecy wave, you will have maximum vibration transfer ie greater sensitivity.
Now the delema, how do I design a rod handle to place my hand at the resonant frequency crest? If i find that spot on the blank with all the guides on, and then install the handle, that spot will now move because I changed the natural frequency by increasing the weight from adding the grip.

I think this makes the difference between a really good rod and one that just seems magic. But I don't know how to engineer it into a rod.

But, that just my opinion



Edited 1 time(s). Last edit at 12/12/2007 03:30PM by Gary Colling.

Gary,
Yes, you are right. How long it takes the vibrations in a rod to return to zero or stop oscillating is called the damping factor not the resonant frequency. The resonant frequency is the frequency of the oscillations the damping factor is the length of time it takes for the oscillations to damp out or return to zero amplitude. For example, glass has a much higher damping factor than graphite because it takes it a lot longer for the amplitude of any vibrations to damp out or return to zero amplitude. Actually, in theory the oscillations will continue forever as the kinetic energy is converted over time to heat. Damping factor is measured by dividing the amplitude of the vibrations after, if I remember correctly 530 cycles, into the initial amplitude. Don't ask me where the number 530 comes from because I have forgotten a long time ago.

Gary and Emory are right, and of course said it much better than I ever could.

Mike, no disrespect, but the relationship between a golf shaft and a fishing rod is actually very similar. You're confusing the application of the graphite shaft - which is built very similarly in both cases - with the physical properties of the shaft. In fact, a loaded golf shaft (i.e., in motion, with grips on one end and a head on the other) acts very similarly under the load (i.e., in-motion) until it hits the ball. If I flex a golf shaft without a load, similar to what I would do with a rod in a store, I'll get a few cycles of displacement and recovery, especially if the shaft is relatively "soft" as for seniors or ladies.

Many golf club custom makers indeed use a resonance device to match the frequency for each club in a set as closely as possible as the lengths progress, and I've seen a half-dozen throwouts set aside because, although they were from the same batch, they didn't fit into a particular target frequency under the appropriate load. The idea is to have the shafts react as similarly as possible (assuming a consistent swing) throughut the entire set even though the club lengths decrease, as with a set or irons or a set of wood. Yes, I've been to not only the custom shops but to the manufacturers, as well. Up to the point of impact, the two things are a lot more similar than not, especially when the golf shafts are specifically designed to maximize flex. The recovery rate in a shaft is important to the ultimate power delivered by the club to the ball. The recovery rate in a rod is vital to the delivery of the lure with maximum speed. Vibration (resonance) in the shaft can result in a decrease in the efficiency of the power transmitted to the ball, and although the time of contact is relatively short, there is an effect. Virfbation in a rod can affect the cast because the follow-on motion of the tip - let alone the whole rod - can interfere with the line's motion as it goes through the guides and tip, as it follows the lure.

Tell you what - let's follow this up at the show over a beer for you, and a diet coke for me. I'll buy.

Uncle Russ
Calico Creek Rods

Whew

(Steve, what model coat hanger do you recommend . . . ?)



Edited 1 time(s). Last edit at 12/13/2007 10:35AM by steve clark.

Russ - actually, if you take a look at high speed photographs of a golf shaft during a swing, you'd be amazed at what a golf shaft goes through. A golf shaft has different forces applied in different manners than a fishing rod. My swing speed with a 45" driver is around 95mph - the head of the club is traveling at that speed at moment of impact. It accelerates to that from 0mph in the arc of my swing. I'm 5'9, my swing arc is pretty short :-) Anyways - the golf shaft is subjected to a trememdous force from the inertia of the clubhead as it resists both forward and lateral movement. The end result is a bending force being applied to the shaft, as well as a torque applied axially to the shaft as it progresses through the swing plane. It's hard to picture - but the orientation of the clubhead is typically about 90-100+ degrees different at the top of the swing as compared to the impact position. The combination of these two forces, and the attempt of the club designer to control their effects, is what leads to a desire to have consistent resonant frequencies - as you noted. In golf, consistent feel from club to club is exceedingly important to a low handicap player. RF is now accepted by the golfing community as the best measurement of club to club consistency. (yes, I used to be a golf club building nut - not anymore, fishing rods are more fun :-)

Anways - getting back to RF - I think it is generally safe to assume that all things considered, a rod with a higher RF is going to be more sensitive than one with a lower RF - HOWEVER - this is but one piece of the overall puzzle. Perhaps it would be safer to say that two blanks of identical length - the higher RF blank has the potential to be more sensitive. This is apparent from other measurements, as in order for it to have a higher RF, it must be stiffer, more lightweight, or (more likely) both.

Someone above noted that the longer the blank, the higher the RF - I believe the reverse to be true.

In a nutshell - I think RF may have some potential as a blank comparison tool - basically doing the same thing Common Cents does, but in a different way. If I had the money, I'd buy a ton of blanks and an optical RF analyzer and go to town :-)

Rich,
You are right about the length of a rod and the resonant frequency. In fact, all other things being equal the resonant frequency of the rod will DECREASE with the square of the length.
I was also a golf nut and I think that you will find that the materials and the construction of blanks and golf club shafts are very similar and the important characteristics are also generally the same. In fact, all of the original manufacturers of gold club shafts were companies that you would recognize as rod manufacturers like G. Loomis and Lamiglas. If I understand what you said above though I only half agree with you. The inertia of the club head has the same affect on the shaft as the inertia of the terminal tackle has on a rod except that because the golf club head is off the center axis of the shaft there is a great deal more torque on a golf club shaft.
If you are interested there is a site [CSFA.com] that is done by a man named John Kaufman who makes devices for measuring the resonant frequency of golf club shafts that has some technical notes on the site that will tell you a great deal about rod blanks. There is a lot of information on resonant frequency, torque and also spine that is really very good information. I have talked to John Kaufman a number of times and he is a very sharp retired mechanical engineer and a scratch golfer who has done quite a bit of research into golf club shafts and most of the information can be applied directly to rod blanks.

Rich,

You wrote: "In a nutshell - I think RF may have some potential as a blank comparison tool - basically doing the same thing Common Cents does, but in a different way. If I had the money, I'd buy a ton of blanks and an optical RF analyzer and go to town."

Here is something to think about.

While with an optical RF analyzer you can measure the frequency of a rod blank, which I will call the RFB, values will be around 250 to 300 cycles per second. True, you will indeed then know the RFB of that blank. But, what are you going to do with that value?

Everything you do to convert that blank into a the rod will decrease that value. However, because of the great number of undefined variables which affect frequency, you have no way of predicting the relationship between the RFB and the RFR or frequency of the finished rod. If one postulates the blank with the highest RFB will always produce the rod with the highest RFR, one would be wrong.

But, the RFB of the blank really doesn’t matter much. A rod builder’s major concern should be the RFR of the finished rod and how one should expect that frequency to affect its performance as a casting tool.

One can create a curve which relates the frequency of a fly rod to the weight applied to its tip. It will start with the highest point which represents the RFR with zero load applied and decrease in value as more load is applied.

If you create similar curves using a series of rods of different “nominal weights” from a single manufacturer, you will get a series of “concentric” curves which do not cross. If you do this with rods from a number of different sources, you will most probably find the curves do cross at various points.

Now, it is not necessary to make all these measurements to define the complete curve, if one knows what part of the curve provides the most useful information about the rod’s performance. In other words, what range of “applied weights” are most useful.

The CCF (Common Cents Frequency) recognizes the most useful “applied weights” should be related to the power of the rod (ERN) and the weight of the fly line aerialized. This also allows one to determine what effects one should expect by changing lines, as it allows one to easily create that portion of the curve which is most useful.

Essentially, what I am saying is that there really is no crying need go to the expense of the equipment necessary to be able to measure RFB or even RFR, when the really useful information can be easily and inexpensively obtained by the use of the CCF.

Bill,
You are off a couple of orders of magnitude on what the resonant frequency of fly rods will be. Most will be on the order of a couple of Hertz or a couple of cycles per second not 250 to 300 cycles per second. I have never measured any rod that was that fast. Maybe you were thinking cycles per minute rather than cycles per second but 250 to 300 would still be pretty high.
With many fly rods, particularly the longer ones, the oscillations are actually slow enough that the cycles can be counted by eye and then that count and a stop watch is all that is required to get the resonant frequency.
Many golf club shops have inexpensive devices for measuring the resonant frequency of golf clubs, they frequency match the different clubs in a set of clubs, and these devices work very well for measuring the resonant frequency of rods. I have gone to a couple of golf shops and found them interested in measuring a fishing rod and very willing to let you spend a few minutes with their measuring device.
Filming or video taping the rod and a watch and playing that back at a slower speed so that it can be counted by eye is another cheap way of making a resonant frequency measurement.