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Fly Fishing Physics

Question:

I prefer to think of the problem in the frequency domain. A stiff rod has a higher resonant frequency (it’s a faster rod) than a flexible rod. As an example, consider casting back and forth repetitively at a rate which switches direction at exactly the moment the end of the line straightens out. Stiffer rods will require you to move back and forth faster than more flexible rods will in order to be switching directions at exactly the right time. The amount of energy stored in the rod bend is small relative to the total amount of energy being delivered to the fly, but is large enough to have an effect on the frequency response of the entire arm/rod/line system. As someone said in a previous post, the rod is acting like a capacitor in an electrical circuit (and I’m pretty sure that the line and air are the exact analogs of a resistor). The whole system acts as a filter which delivers the optimum amount of energy to the fly when the arm moves back and forth at a certain frequency. If you must think of this system electrically, then you are very likely to bark up the wrong tree. I have given this much thought. If you want to continue, a better, but by no means foolproof model is that of a tapered transmission transmission line driven at its end through an impedance network. A better approach would be to model the continuous combination of line and rod as a series of small nonlinear network sections. Then it may be possible to use some of the electronic modeling programs such as SPICE to obtain a solution. As far as I know, the people who did computer simulations did model the system with the more direct mechanical rather than electrical equivalents of the line. Then, instead of using a canned program such as SPICE, the solved the differential equations directly or with a DE solver from a numerical method library. William Buchman

Response:

"On Hauling: Line speed increases because the haul, essentially, makes the rod bend deeper than it would from a casting stroke alone. Which implies that the rod stores energy. Which of course it does. On the ideas of the rod: The idea of the rod is to transfer the energy of the arm to the line in such a way that a cast is more easily accomplished than it would be if you were swinging a stick. As such, the rod stores and releases energy on every back cast and every forward cast. . ….more stuff snipped…" William Buchman responded: "I must disagree with you. You are confusing causes and effects. Line speed increase (acceleration) provides the force that makes a rod bend more, not the other way around. While true that bending of the rod helps one to cast, bending by itself does not account for much of the energy imparted to the line. You do not really want the rod to store energy, either kinetic or potential. Kinetic energy is reduced by going to light-weight rod material. Potential energy (bending of the rod) is the price we must pay to obtain easier casting because of our lack of skill. William Buchman" William, I agree with you, sort of. During the final portion of a casting stroke, when one tugs (hauls) on the line to make it go farther, it is the line’s _resistance_ to acceleration (inertia) that causes the rod to bend deeper than it otherwise would have. If your rod was perfectly stiff and unbendable, and your wrist as strong as iron, then a haul would result in pure acceleration of the line. But the rod is flexible, so two things happen. One is a small acceleration of the line, and the other is extra loading of the rod as a result of the line’s inertia. I maintain that this second phenomenon, the extra loading, is more important when it comes to the MAIN event of line speed increase, which occurs when you stop the rod, let go of the line, and the rod unloads that extra bit of bend back into the line. THAT’S when line speed really increases. A haul is like pulling back on a slingshot an extra little bit just before you release the pocket. Bending of the rod does not account for ANY of the energy imparted to the line. It ALL comes from the caster. The bending and relaxing is how a rod modulates, or filters the energy inputs of the caster. There is no inherent price paid because a rod bends. The potential energy contained in the bend does not magically disappear. When you stop the rod and it returns to its relaxed state it releases that energy into the line. Sure, there are small losses associated with air resistance, imperfect elasticity of the rod, and a myriad of other things, but, they’re small. There’s no need to lament the fact that it’s more difficult to cast 80 feet of fly line with a stick. Trevor

Response:

In response to Ralph H’s 10/20/97 post: On Hauling: Line speed increases because the haul, essentially, makes the rod bend deeper than it would from a casting stroke alone. Which implies that the rod stores energy. Which of course it does. On the idea of the rod: The idea of the rod is to transfer the energy of the arm to the line in such a way that a cast is more easily accomplished than it would be if you were swinging a stick. As such, the rod stores and releases energy on every back cast and every forward cast. On energy and wires: All energy IS imparted by the arm of the caster. But not all that energy is transferred instantly to the fly line. The rod, because of its springy nature, stores some of that imparted energy in the bend that is called a "loaded" rod. When you stop the rod it springs back to its relaxed state, delivering the stored energy to the fly line. It’s a GOOD thing that a fly rod stores energy. To use your electrical analogy; if a fly rod was simply a wire and not some device that modulated the energy input of the caster, then it would be a lightweight stick, perfectly stiff and unbendable, and everything that a man or woman could do with a fly line and a fly would depend on their ability to manipulate that stick. It would be very, very difficult. Trevor

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One of the misconceptions about fly casting is that the rod stores a lot of energy. That is not the case. Most energy gets transferred by the hand to the rod to the line without much actual spring storage in the rod.

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A rod is like a leaf spring. When it flexes, it stores potential energy which it releases as kinetic energy as returns to its relaxed conformation. You can prove this for yourself. grab the end of your rod and flex it. Now do not move. There is not kinetic energy because nothing is moving. Now release the tip of the rod. It literally springs straight. The movement of the tip = kinetic energy. This kinetic energy did not magically appear ex nihilo; it was produced by the release of the potential energy stored in the flexed rod. IOW, if a rod flexes, then it stores energy. End of story. Almost. First, a rod does not store the energy for very long. Second, it is possible to cast with a broomstick that does not flex and that therefore does not store potential energy. A final point. You will probably notice that it is much easier to cast with a rod than with a broomstick. This is an indication of the importance of the rod’s ability to store energy. While it is true that the rod can store SOME energy, it never gets more than about 15% of the energy imparted to the flyline. The fact that you can cast with a broomstick indicates that a flexible rod is not NECESSARY. The rod makes it EASIER to cast. It removes much of the skill required to cast with a stick. By flexing it makes it possible to propel the end of the flyline in a relatively straight line allowing tight loops to be formed. The small amount of energy stored in the rod makes up for lack of skill, but is not very significant toward the speed of the flyline. William Buchman

Response:

I’ll make a few more comments without detailed quotes. I agree that being a good fisherman is more a matter of skill than knowledge of differential equations. Nevertheless, the subject is of interest. There is a large literature of fly fishing stories. Many of them are about the social, and antisocial, aspects of fishing and not about the skill and technique of fishing. That does not make the subject unworthy. Neither is the physics aspect unworthy. In terms of other physical descriptions, a little bit of mathematical modelling is not out of place if you are making assertions. For example, there was disagreement expressed with regard to my statement that stored energy in the rod is usually not a good thing. Much of that energy gets put into putting waves into the line. Good rods absorb that energy at the end of the cast. William Buchman

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(snip) : The amount of energy stored in the rod bend is small relative to the total : amount of energy being delivered to the fly, but is large enough to have an : effect on the frequency response of the entire arm/rod/line system. As : someone said in a previous post, the rod is acting like a capacitor in an : electrical circuit (and I’m pretty sure that the line and air are the exact : analogs of a resistor). The whole system acts as a filter which delivers : the optimum amount of energy to the fly when the arm moves back and forth : at a certain frequency. (snip) You got it! Optimizing energy transfer, and that energy is kinetic, ie velocity. The rod does store energy, but the amount is less important than when it absorbs, and discharges the energy. You need high line velocity to get distance. Did you know that for a proper hockey slap shot, the stick MUST hit the ice just ahead of the puck? This loads the stick and releases on contact with the puck all in the blink of an eye. Believe me when you get just the right amount of ice, that puck goes like a bullet. With proper technique and timing, one day I may do the same with my fly line! Garry N. Boychuk, P.Eng. mechanical engineer, flyfisher, Zone 6b gardener

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The greatest flyfishing psychic is John Alden Knight…. — TimW Halfordian Golfer

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I was wondering how long it would take this thread to go non-linear. Congratulations! — -dnc- "FiddleAway" wrote I prefer to think of the problem in the frequency domain. … …. The whole system acts as a filter which delivers the optimum amount of energy to the fly when the arm moves back and forth at a certain frequency.

BillyFish wrote [SNIP] – Hide quoted text — Show quoted text – A better approach would be to model the continuous combination of line and rod as a series of small nonlinear network sections. Then it may be possible to use some of the electronic modeling programs such as SPICE to obtain a solution. As far as I know, the people who did computer simulations did model the system with the more direct mechanical rather than electrical equivalents of the line. Then, instead of using a canned program such as SPICE, they solved the differential equations directly or with a DE solver from a numerical method library.

Response:

By the way. The Scientific American article mentioned by a number of posters on this thread was, in part, based on work done by Buchman and Moser. William Buchman

So tell me, isn’t it true that you can generate a higher maximum tip speed with a springy rod than with a rigid rod. After all, the acceleration produced by the spring at the end of your stroke is added to your best effort. A little bit of spring plus the maximum speed with which you can move your arm will always be greater than the the maximum speed you can generate by yourself. No. By the time that the cast is finished, there is not much the rod can do to add significantly more energy to the line. What you would like, is to drive the tip of the line with as much force as you can over as long a distance as you can in as straight a line as you can. To the extent that the rod gets loaded (bent), the distance that the line is driven gets reduced. That limits the energy transfer. What a good rod does, is to move the tip of the rod and the flyline in a straight line. There are strobe photographs to prove it. I believe the Scientific American article has printed that. William Buchman

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By the way. The Scientific American article mentioned by a number of posters on this thread was, in part, based on work done by Buchman and Moser. William Buchman

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Then there’s the problem of hauling. I think most fly-casters agree that a haul adds power to a cast. And from everything I’ve read, all the casting luminaries tend to agree that hauling essentially is a way to make the rod bend deeper than you could bend it with a casting stroke alone.

I think hauling increases line velocity, not rod flex. — Bob Jarvis Mail address hacked to foil spammers!

Response:

SNIP it’s likely a bad thing if a rod stores energy – if it did the release of that energy would be difficult to control. Hence errant vibrations in the rod that impair casting. Any energy transfered to the rod should be imparted to the line when desired and a minimum of energy should remain in the rod.

If this were so, then I should trow away my 2 weight rod (well, actually, my brother’s 2 weight) and rely on my 50 weight rake handle for casting all my lines. It would hardly flex at all, it would store almost no energy, and it would be the perfect rod. I could even duplicate the trajectory of a real rod tip by bobbing the rake handle down briefly in the middle of the stroke. In fact, a "rake handle" would make an excellent fly rod **IF** 1. It were light-weight. You do not want to put kinetic energy into the rod. Graphite composition and the like enable casting with little rod kinetic energy. 2. Your skills were up to the task. You would have to start a forward cast with your hand back and up. Bring your hand forward and down. Then forward and up. All this is to try to keep the tip going along an approximation to a straight line. Aside from acting as a lever, a good rod will have no spring to it than required to compensate for *your inability* to use a rigid stick. William Buchman

Response:

******* In response to Ralph H’s 10/20/97 post: On Hauling: Line speed increases because the haul, essentially, makes the rod bend deeper than it would from a casting stroke alone. Which implies that the rod stores energy. Which of course it does. On the idea of the rod: The idea of the rod is to transfer the energy of the arm to the line in such a way that a cast is more easily accomplished than it would be if you were swinging a stick. As such, the rod stores and releases energy on every back cast and every forward cast. ****** I must disagree with you. You are confusing causes and effects. Line speed increase (acceleration) provides the force that makes a rod bend more, not the other way around. While true that bending of the rod helps one to cast, bending by itself does not account for much of the energy imparted to the line. You do not really want the rod to store energy, either kinetic of potential. Kinetic energy is reduced by going to light-weight rod material. Potential energy (bending of the rod) is the price we must pay to obtain easier casting because of our lack of skill. William Buchman

Response:

A rod is like a leaf spring. When it flexes, it stores potential energy which it releases as kinetic energy as returns to its relaxed conformation. You can prove this for yourself. grab the end of your rod and flex it. Second, it is possible to cast with a broomstick that does not flex and that therefore does not store potential energy. A final point. You will probably notice that it is much easier to cast with a rod than with a broomstick. This is an indication of the importance of the rod’s ability to store energy.

I have a book with some discussion of the physics of casting (The Art and Science of Speycasting by Mike Maxwell) the author is also an engineer - he disagrees with the ‘energy storage’ theory. He say that if you strip a length of line (say 45 feet) from a rod and reel hold it upright and have someone stress the rod by pulling on the line and bending the rod then release the line the line will not ‘cast’ forward from the energy thus stored. You could not acheive a cast whatever the energy stored in the rod right to the point of braking the rod. Rather a rod is a ‘transducer’ of energy of a sort. It converts and directs the energy of the casters arm movements. Ralph H remove "(take_this_out)" for email reply.

Response:

hauling increases distance by increasing line speed not by imparting additional power to the rod; increasing the speed increases the force in the moving line not the rod. The idea of the rod is to transfer the energy of the arms to the line not to store energy in the rod. I’m not convinced that the rod stores little or no energy. However, I’d be interested to read your entire article, or any article that offers a well-supported explanation of fly-casting mechanics.

it’s likely a bad thing if a rod stores energy – if it did the release of that energy would be difficult to control. Hence errant vibrations in the rod that impair casting. Any energy transfered to the rod should be imparted to the line when desired and a minimum of energy should remain in the rod. If you think of it there is no energy of significance (unless only in a negative sense) stored in the rod but all energy is imparted by the arms of the caster. to use an electrical analogy; a rod is more like a wire than a capacitor. A capacitor stores energy, energy remains after the current source is removed. A wire simply moves the current. Ralph H remove "(take_this_out)" for email reply.

Response:

One of the problems associated with explaining fly rod casting physics is the common misinterpretation between velocity(speed) and acceleration(rate of change of velocity). The important point to achieve a good cast is to *accelerate* the line through the casting stroke. This is achieved first by the arm movement. moving the rod, acting against the inertia of the line and the rod. As the arm movement accelerates, inertia increases. At the end of the arm stroke, the rod unloads(straightens) adding further acceleration to the line. A tiny flick of the wrist will add further acceleration, as will a small haul on the line. This notion of acceleration can be seen graphically when watching someone doing an exaggerated haul on the line, ie moving the line more than a foot or more. It is simply too slow. A short sharp, just a few inch pull (haul) will achieve greater line acceleration. The key to a good cast is to gain the maximum line acceleration in the back cast to build up the maximum inertia in the line, rod and arm. then on the forward cast use this inertia to fully load the rod prior to the forward cast. Adding acceleration to this inertia through the forward cast will achieve more distance. In the North island of New Zealand where we cast heavy nymphs and flies, often a long way, a trick to gain full rod loading is to allow the nymph to hit the water on the false casts to further load the rod and build inertia. This trick is commonly used when saltwater fly fishing. Tony Bishop Taupo New Zealand http://bishfish.co.nz – Hide quoted text — Show quoted text – : : He say that if you strip a length of line (say 45 feet) from a rod and reel : hold it upright and have someone stress the rod by pulling on the line and bending the rod : then release the line the line will not ‘cast’ forward from the energy : thus stored. Right — though it does store some energy (it’s flexed, so it must), since the line goes forward a bit. I think William Buchman’s phrase of "a lot of energy" is the key: One of the misconceptions about fly casting is that the rod stores a lot of energy. That is not the case. Most energy gets transferred by the hand to the rod to the line without much actual spring storage in the rod. : Rather a rod is a ‘transducer’ of energy of a sort. It converts and directs : the energy of the casters arm movements. It probably smooths out and concentrates the release of energy more near the end of the stroke, when the line is straight and can be directed easier and sent out farther. JonCook.

Response:

If this were so, then I should trow away my 2 weight rod (well, actually, my brother’s 2 weight) and rely on my 50 weight rake handle for casting all my lines. It would hardly flex at all, it would store almost no energy, and it would be the perfect rod. I could even duplicate the trajectory of a real rod tip by bobbing the rake handle down briefly in the middle of the stroke. If you think of it there is no energy of significance (unless only in a negative sense) stored in the rod but all energy is imparted by the arms of the caster. To use an electrical analogy; a rod is more like a wire than a capacitor. A capacitor stores energy, energy remains after the current source is removed. A wire simply moves the current.

Exactly. A wire just moves the current. It does not modify, smooth out, or redirect the current. It does not, to use a computer analogy, process the current. Springy rods (that store energy by virtue of being springy) do process or modify the input our arm provides. That is why the choice of rod/processor is so important. A rod that springs too much or too little is just no fun. By the way, rods do not finish unflexing until your casting hand has stopped. That means that they are like capacitors because energy does remain after the current source (the movement of the casting hand) is removed. Now, you are probably rifght in the sense that the quantity of energy stored in the flexure of the rod is not very large. In another post someone suggested an experiment where an immobile, flexed rod tries to cast a line. It does not do very well. However, in terms of its impact on the cast, that energy is extremely important. When the rod unflexes at the end of the stroke, the rod tip is travelling (under pressure from the spring) faster than we could wag the tip of a rigid rod. Another poster mentioned the trick of dropping your back cast so your nymph drags in the water as you start your forward stroke. The advantage that this tactic imparts is due entirely to the extra load it imposes on the rod. IOW, it helps because it flexes the rod more = it increases the energy stored in the rod. Scientific American ran an article on the physics of flycasting a few years ago. It emphasized the importance of the rod qua spring. That is where I got that bit about tip speed. Keep your stick on the ice, Thos.

Response:

Mr. Buchman: The idea that the rod doesn’t impart much energy to the fly line suggests that loading the rod has no affect on the amount of power you can put into a cast. I’m frequently wrong, but I have a difficult time believing this. If the rod doesn’t impart much energy to the fly line, then what difference does it make what kind of rod we cast with? A soft rod should cast as powerfully as a stiff rod. And wouldn’t cane cast as powerfully as graphite? I know that if you have two rods–a stiff rod and a soft rod–and bend them equally throughout the casting stroke, the cast made with the stiff rod will be more powerful. If the difference isn’t in the energy stored in the rods (that is, the stiffer spring storing more energy for the same amount of bend), then what is the difference? Then there’s the problem of hauling. I think most fly-casters agree that a haul adds power to a cast. And from everything I’ve read, all the casting luminaries tend to agree that hauling essentially is a way to make the rod bend deeper than you could bend it with a casting stroke alone. I’m not convinced that the rod stores little or no energy. However, I’d be interested to read your entire article, or any article that offers a well-supported explanation of fly-casting mechanics. Sincerely, George V. Roberts Jr.

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Fly Fishers of Usenet, My high school physics class is doing a large project on the physics involved in fly fishing. Our specific focuses include sonar (as used on fishing boats), line strengths, and fly casting. If anyone has any good information pertinent to the physics aspect of this wonderful sport, it would gladly be appreciated. (We’ed even mention your name in the credits if you so wish!)

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If you haven’t already found this site you should check it out. The Physics of Fly Casting http://www.mit.edu:8001/people/kommers/fly.html A discussion of the physics involved in a fly cast including a series of MPEG movies which show the results of the author’s simulations. — David V. Green WWW.GreenFly http://www.greenfly.com 310.204.4042

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There ar a number of computer programs for simulating casting of lines by Cristopher Barnes who was a student at Reed College in 1992. This was for a BA. Previously, T. M. Robson, professor of physics emeritus at McGill University published a paper in, I believe, the American Journal of Physics. There have been a number of less technical articles including one by me and a colleague in the Flyfisher about ten years or more ago. Some of this work has been reported in the Scientific American’s Amateur Scientist column. Previously, the same column had a very good article on the optics of fly fishing. I figure that with these hints, you should be able to find these articles as easily as I can. William Buchman

Response:

My high school physics class is doing a large project on the physics involved in fly fishing. Our specific focuses include sonar (as used on fishing boats), line strengths, and fly casting. If anyone has any good information pertinent to the physics aspect of this wonderful sport, it would gladly be appreciated. (We’ed even mention your name in the credits if you so wish!)

The late Al McClane tried about 20 years ago to sort out the physics of fly casting once and for all, modeling the rod as a flexible cantilever structure that could be loaded and unloaded, i.e. store and release energy. Check his books, starting with his Encyclopaedia. There was a followup approx. 1980 in the Scientific American (reference now lost….) — | Donald Phillipson, 4180 Boundary Road, Carlsbad Springs, | | Ontario, Canada, K0A 1K0, tel. 613 822 0734 |

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The late Al McClane tried about 20 years ago to sort out the physics of fly casting once and for all, modeling the rod as a flexible cantilever structure that could be loaded and unloaded, i.e. store and release energy. Check his books, starting with his Encyclopaedia. There was a followup approx. 1980 in the Scientific American (reference now lost….) ******* One of the misconceptions about fly casting is that the rod stores a lot of energy. That is not the case. Most energy gets transferred by the hand to the rod to the line without much actual spring storage in the rod. William Buchman

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