I'm back ! Soft rods /Acceleration / Over & Underlining

````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````

Good question from Liam Duffy . Think this one out carefully before you answer:-

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Gordy,

Oops, I timed this wrong – just as you are leaving town. Well, no hurry. I’ll look forward to your response whenever you get back.

I am a lurker in your network 99% of the time, but I read it all, try to digest it all, and save what gives me new insights. Thanks very much for all you do with this.

I want to raise an issue that you dealt with some time back in which you were led to change your point of view. But I agreed with your former position, and have not been convinced that I should change mine.

It is the matter of whether a good cast uses a constant rate of acceleration or an accelerating rate of acceleration (I think you called it an "accelerated acceleration", but I think "accelerating acceleration" is more accurate). I recall that Bruce Richards convinced you that his studies with the casting analyzer showed that a constant acceleration was what was needed. I do not know what he and his cohorts measured or how they measured it, and I am neither an engineer or physicist, but my practical observations on flycasting and on being a passenger in an airplane have led me to believe otherwise.

Here is my case in layman’s terms.

In making a cast the goal of the loading process is that the rod be gradually and progressively loaded to the maximum (or "optimum" for that particular cast) just as you reach the stop position. We begin with the rod straight and need to finish the power part of the cast with the rod optimally bent. I relate this to the experience of what happens to my body when I am a passenger in an airplane.

When the pilot opens the throttles at takeoff, the inertia of my body weight is trying to keep me back where I came from, and I am pushed back into my seat back. As long as the plane continues at that acceleration I continue to feel the same amount of backward pressure (it reaches a state of equilibrium for that acceleration). When the pilot backs off on the throttle the backward pressure eases up, but if something called for the pilot to open the throttle even more than he had it opened at takeoff the resulting inertial pressure of my body against the seat back would be even greater than that at takeoff, because the rate of acceleration was greater against the fixed inertial mass of my body. But again at that acceleration my body and the seat back would reach a point of equilibrium as long as that (rate of) acceleration was constant.

Now instead of my body against the seat back let’s consider the mass of the fly line working against the rod. It seems to me that if we establish a fixed acceleration at the beginning of the cast the rod will flex the amount it needs to to move the mass of the line against that specific acceleration and will simply maintain that amount of flex/load throughout the rest of the cast (a state of equilibrium). The more deeply you want to load the rod the more energy/speed/acceleration you must apply at the point in time in which you want it loaded to that extent. A constant acceleration of X feet per second per second cannot exert a variable force on a fixed mass (the line trailing the rod tip). We want the rod to progressively flex deeper and deeper all the way to the stop, and so we must be accelerating in a way that denies the achieving of equilibrium. To me, that can only mean a constantly accelerating acceleration. Because the line is gaining speed we must keep accelerating the rod not only faster than the line can catch up with but so much faster that the line keeps falling farther and farther behind, thus progressively loading the rod more deeply. I don’t believe that can happen with a constant acceleration.

The perfect example of this is right before our eyes when we attempt to make a longer cast. To make a longer cast we want to load the rod more deeply, so we make a haul. That accelerates the acceleration even more than was being done with the regular cast, and the result is a deeper load (and faster line speed). And if the haul deepens the load of the rod by accelerating the acceleration, how do we deepen the load of the rod when we don’t haul? There is only one way to do it --- the same way --- by accelerating the acceleration throughout the cast itself.

I realize that most beginning fly casting pupils don’t need to be burdened with this complicated stuff. But I do think they need to understand that "speed up to a stop" does not simply mean getting faster throughout the power part of the cast, but means speeding up at a rate that makes the rod tip fall progressively further behind, thus loading the rod more deeply all the way to the stop. That, in my understanding, requires an accelerating acceleration.

Please share this with the group and share your insights and your knowledge of physics to point out where I am wrong, if I am..

Dermon Sox

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dermon: Bruce Richards and I have discussed this at length. I do think that we can have a certain amount of accelerated (or, "accelerating") acceleration if we consider the cast as a whole including the translational as well as the rotatory phases .... especially considering that there is very little acceleration of the rod or the hand as we start with translation, and MUCH more as we go into the rotatory phase. The more, "accelerating acceleration" we have instead of true CONSTANT acceleration, the more the loop suffers. Too much, and we end up with a tailing loop.

In studying this with the videos and the Casting Analyzer, Bruce and Noel Perkins noted clear evidence that during the ROTATIONAL phase, that the best formed tight loops were produced with CONSTANT ACCELERATION, not accelerating acceleration.

You are correct in that you cannot keep bending the rod unless you are moving it at ever increasing velocity.... but this IS achieved with constant acceleration.

If we wish to make a longer cast, we can load the rod more deeply with greater acceleration, to be sure..... but it can still be constant acceleration.

Be certain to check out Bruce Richards' article on ACCELERATION on p. 7 of this latest Winter edition of the Loop. I think he has made this crystal clear. (Go to:

http://www.fedflyfishers.org/loop.php ..)

Gordy

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Gordy,

I am confounded about a question that comes up periodically (such as on my orals). I know that I got the short answer right. The question was,"Is there ever a time that you would want to underline or overline your rod?" SA: Yes. When and why? Overline-short amount of line out of the rod and I need to load it quickly. Also for new students so that they can feel the rod load. If I were in a distance competition with long, stiff rods and needed to load that stiff rod (a very unlikely circumstance, indeed, at least for me). Those all seem straight forward. Underline: desire a softer landing, practicing loops when you can't feel a lot of load, long cast into a head wind. The last leaves me with lots of questions. Here is my thinking. Please, correct me if I run astray. With a heavier weight line on the same rod with equal amounts of line out of the rod tip there has to be more flex in the rod and thus more counterflex which should result in a bigger loop size. The bigger loop will not be as aerodynamically efficient-more surface area exposed both in the loop and line size itself (although the difference is miniscule) and thus more wind resistance. With the lighter line you could carry 5-6 more feet of line in the air to get the equivalent weight of the heavier line. Will this not then flex or load the rod the same as the heavier line the only difference now being that there is more line being carried. Now lets factor in the wind. At what point does wind resistance make carrying more line a null factor? In other words as the mass of my lighter line decreases the velocity increases but the wind resistane increases geometrically. At some point they are going to counterbalance each other and there is no longer any advantage to having underlined. Would overlining be better at this point say by 2 line weights and not carrying a lot of line out of the rod tip as this would result in a tight loop and an increased velocity (KE=1/MVxV). The answer to my questions may be in the paper that Noel Perkins wrote about falling lines and speed but my math is too many years removed to appreciate his paper. I would really like to understand this and not feel like a dummy.

Jim

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Jim...

You got it just right with respect to overlining. Need no more comment from me on that one.

It is UNDERLINING which is so confusing to many. Here is my take:

Even when underlining by two or three designations, one can make perfect loops as long as a nearly straight line path of the rod tip exists, and the rod is unloaded very close to the level of the oncoming line. This is true whether or not we are casting into a wind, and whether we are carrying a heavier line or not, unless we have exceeded the capacity of the rod and /or the angler's casting ability.

Remember when we put this to the test as we made casts carrying more line than we as casters could carry efficiently. Loops suffered, and so did both distance and layout.

For increased distance, we must consider that (up to the point that the line gets thinner), as we let each 5' - 6' of line out of the rod tip beyond the first 30' while false casting, we are carrying approximately one more line designation, ie. weight.

Example: I am using a 7 wt. rod. My line is a long belly WF5F. As I false cast with 50' of line carried out of the rod tip, I'm actually casting a size WF9F line ! I'd load about the same if I started with a WF9F line and limited the amount of line out of the rod tip to the first 30'.

In the event that I stick with a WF7F line on my 7 wt. rod, and carry a full 50' of long belly line, I'm actually casting with a WF11F line. I'll need a rod with enough strength to carry that. (Again, most modern fly rods will do that.) As Tim Rajeff pointed out at our Continued Education Course last month, all rods of the same designation are not necessarily equal.... one 7 wt. rod may be much stronger than another.

To put it another way ; one limiting factor is the rod. My 7 wt. rod may be able to handle a wide range of line sizes OR NOT. Most modern rods can do that.

As you point out, wind may be an important limiting factor, because with a strong wind blowing either at me or from behind, I may not be able to handle 50' of line while false casting.

(Mathematically, without using Noel's calculus formulae, at one end of the differential scale, I can handle a maximum amount of line (no wind) and at the other end ... the extreme, I can handle no line at all (when the wind is so strong I simply can't make a cast.) In real life, the truth lies somewhere in between.)

Remember, that as long as the fly line loop is unrolling, it is falling slowly balanced by conditions providing lift. Once the loop has stopped unrolling, it falls much faster.

When casting into the wind at most wind speeds encountered when fishing, the fact that the small tight loop projects energy better than the wide loop in the direction of the target is more important than the fact that this tight loop has less wind (air resistance). THAT RELATIVE DIFFERENCE CHANGES AS THE WIND GETS STRONGER until we get to the point that wind (air) resistance is most important, and, finally, to the level that it is of overwhelming importance as we get to the point where we can't overcome it at all.

Gordy