Living the Bamboo New Age: the italian job – Part 2
text by Massimo Tirocchi
This brief article aims to go a little more deeply into some aspects that have been described in the previous article published in the October Issue of the Power Fibers magazine with the title Living the Bamboo New Age: the Italian Job.
As usual, I’ll approach these technical issues using simplicity, avoiding a pure mathematical and scientific approach in order to make these ideas easily understood and discussed.
Does it make sense to speak about Fast or Slow rod actions?
About this point several and very exaustive materials have been written in the past years, so now we recall some of those concepts using them to approach a new way to describe the action of a fly fishing rod. Dr. Hoffman and others have shown in the past (“Fly Rod Response” published in the January, 1998 issue of the Journal of Sound and Vibration) that talks about rods with fast or slow action. It means almost nothing. Also the very common method to lock a rod on a table and put a weight on its tip can show us how the rod bends, but the information we can get from this approach are not exhaustive enough to understand the real behavoir of our fishing tools during their use.
In fact, if we want to achieve an objective starting point of view about how a rod behaves during casting, and also if we want have some more info to give the right line weight to that rod, we should talk about its natural frequency. In the October issue article, we assumed that frequency is equal to stiffness/weight. Starting from this point we also said that stiffness is not equal to “fastness” otherwise a broomstick should be the fastest rod in the market, and also the cheapest one. (This point is really interesting if we want to find an answer to this question: how does hollow building affect the bamboo rod’s action? For sure hollowing a rod we lose something in terms of stiffness, but it is also true that we get an advantage in terms of weight lost.) We also said that rods with an higher natural frequency (usually rods with very light tips) have a higher response to the input of the caster and this makes it easier to perform casting with high line speed (yes…!!!! fast or slow can be the way that line reaches the water; a rod can’t be fast or slow, a rod can have an higher or lower response to our input and this is related to its natural frequency).
Despite the natural frequency, the rod gives to us a lot of information. We can try to make a little step beyond it trying to reach what we’ll call the Reactive Rod.
To do this let’s recall some concepts known to most of us. I’m talking about translation and rotation movements. The process aimed to transfer energy from the caster to the line (fly) goes through two main subprocesses. We don’t want to talk about energy in general, we want to talk about how this energy becomes speed applied to the line. A lot of studies say to us that we give speed to our line going throught those two subprocesses: translation and rotation. They also said to us that between these two subprocesses the one that allows us to give the line the biggest quantity of speed is the rotation movement (we also know that rotation must be used very carefully with classic style bamboo rods).
It’s a quick and sudden rotation (I like to see it as an opening and closing camera diaphragm – quick and short) that as we saw in the article published in the October issue in which we force the rod to go beyond its natural frequency. In this moment (we called this the Boost moment) the rod reaches the 2nd or the 3rd harmonic (also known as 2nd and 3rd mode of vibration). The rod assumes a shape like a wave split in 2/3 parts and we’ll see that each interruption point is represented by a node.
When we force the rod into such vibrations, the frequency is equal to two or three times its natural frequency. If we can understand which is the best way for the rod to react to this high vibrations we can also understand the character of a Reactive Fly Fishing Rod.
The Reactive Rod
First of all, let’s try to make a definition of what a reactive rod should be. The reactive rod should be a rod that allows to the angler to transfer as much speed as possible to the line in the shortest amount of time. From this definition we can understand that the design of the taper must be able to manage, in the best way, the tradeoff between energy storing capacity and how fast this energy will be transferred to the line in terms of speed.
A brief and a little bit technical explanation is needed. The total energy of the mechanical wave is obtained by the sum between:
- Kinetic energy: that is the energy that each portion of the rod possesses because of its transverse velocity oscillation.
- Potential energy: which is the energy due to elastic deformation of the rod. A very useful concept for us is not the total amount of the energy but the Density of these two unit measures.
- Kinetic energy density: it is maximized when the rod vibrations are at their maximum.
- Potential energy density: it is maximized when the rod gets its maximun deformation.
If we assume these definitions a Reactive Rod could have the following features:
- It must has a natural frequency > 3 to 3.5 cycles per second.
- It must be very sensitive in the last 10 inches of the tip (this will facilitate the narrow loops or at least very tighted loops).
- It must have the butt and the tip perfectly syncronized to be able to work like an orchestra above all in the moment we force the rod until the 3rd harmonic.
The first two points should be quite clear. Let’s go deeper above the third one. Looking at the image below we can make the followings considerations:
- In case A (typically a rod with a low natural frequency) the 3rd harmonic shows us that there is a lot of energy, but it needs a long time to reach the line.
- In case B, we have a 3rd harmonic quite nice, because the waves store some energy and they are ready to quickly transfer it to the line.
- In the case C, we see a classic stiff rod with a tip action. Here the energy stored is less than the other two cases. Despite this, it will be the faster to reach the line.
Between the three functions described, the one that is better than the others showing what a Reactive rod should be is the case B. In fact it is the one that allows the caster to give his/her line the highest speed in the shortest time.
In other terms we could also say that maybe a parabolic action rod is able to store more potential energy than a progressive action rod. The parabolic rod won’t easily to transform all that potential energy in kinetic energy and so in speed, while we force it to reach the 3rd harmonic.
In the scheme below we also see what a reactive rod should do:
We also see what the meaning of a tip and a butt working like an orchestra is. From this point of view a good taper is a taper where all those “bubbole” of energy (bends) are managed in the right way. Trying to understand how they will work one on the other one is the challenge. All those bends that store energy must be very quick on transferring the maximun energy stored in the shortest time to our line. We can also see that in these conditions the last part of the tip will receive an overcharge of energy coming from the other two bends that we see in the last first part of the tip (near to the ferrules) and the last part of the butt.
In other words, making a comparison with the world of electricity energy, what we are looking for, is a rod able to maximize its “WATT” = the flow of energy that passes through the rod in the unit of time.
These considerations have been done knowing that:
- The perfect rod doesn’t exist.
- A lot of more variables play in the fly fishing casting a strategical role.
- We can get a lot energy also from the tension of the line.
- A great scientist said: “the map is not the territory”
Consider also what has been said about the 3rd harmonic is something that could be very useful for
an experienced caster, but it could be very hard to feel for a beginner. The 3rd harmonic gives us a lot of energy but if the caster doesn’t manage it in the right way, its effects to the casting could be very bad. As you can see in the following pics the vibrations have not been managed and you can see the very bad result in term of loop. In fact the tip has not been managed by the caster and it bends too much, opening a wide loop.
In fact, during the casting moment called boosting, the caster must have a great sensitivity to create the conditions that bring the rod to the 3rd mode of vibration. Less than one second after this, he/she must be able to avoid all the negative influence. On TLT Casting Style, this is done avoiding the stop moment and opening the hand one moment after the 3rd harmonic has been achieved. In fact, if you open the hand in that moment you’ll “freeze” the rod cutting it into the main pivot rotation.
From a rodbuilder point of view I can say that a very critical point in the design of a taper for a such kind of the rods is for sure the butt. Anyway I hope that these points could give some inspiration to the bamboo builder during the design of their taper.
When I think high performance bamboo rods I like to imagine them with the same features described by Italo Calvino in his “American Lessons.” In his unforgettable and prophetic “Lezioni Americane” (American Lessons), Italo Calvino created a lucid and straightforward introduction to the literature of the third millennium which he filtered into five categories: lightness, rapidity, exactitude, visibility and multiplicity.
These ideas are always “a work in progress.” They come up through an istinctive approach and through intuition, so they could be right or wrong. Any considerations, suggestions, different ideas will be very welcome and analyzed with great interest.
(This article has been published on the Power Fibers On Line Magazine – Issue n.46 January 2012)