The practical side of considering loops as waves: Teaching and Self Improvement

[Graeme H]

In this thread hosted within the physics sub-forum, I stated that I've improved my own casting ad teaching by applying the concept the "loop as a transverse wave". Several people wanted to know how I'm doing that, so rather than hide that information in an esoteric (scary?) part of the forum, I promised I'd share it where people might find a use for it.

For me (and I hope most people here), playing in the abstract world of physics is not an objective in and of itself. I need to be able to relate the stuff I think about to actual casting and how I might improve my own. Indeed, the whole reason for thinking about the physics is driven by that need to improve my casting - there is no other point as far as I'm concerned. I don't care at all for equations and models - there MUST be an application for it.

In that thread in the physics sub-forum, I said:

For example, these things are easier to do or explain when the loop is treated as a wave:

• Morphing loops
• Excessive overhang
• Landing an aerial mend in the correct location
• How snap casts work
• Increasing line carry
• Check hauling (forced turnover)
• Roll casting
• The 180° Rule
• Explaining how pull back works
• Controlling underpowered curve casts

I'm going to post a series of items that might be of interest to people wanting to improve their own casting or teaching. Feel free to debate how they might help casting or teaching, but please refer back to this thread for discussions on the physics I'm using here. I don't want to pollute a teaching sub-forum with shit that will just make people give up on it. The physics forum is the place for those discussions and I won't address any of your physics questions here. Either accept what I'm stating (however reluctantly) and use it to help your casting/teaching, or don't accept it and just move on.

As I stated in that other thread, I mostly apply my understanding of waves (such as it is) to controlling the waves in the line during a cast. That is, controlling their shape, size, and speed over the ground and through the line. The main waves in a cast* include:

• Mends
• Loops
• Unintended wiggles in the rod leg
• Snap casts
  
• Tailing loops

The behaviour of waves in a string depends on tension and the "linear mass" of the string. Think of a guitar string: the tighter the string and the thinner the string, the higher the note (both give higher frequency). Reduce the tension or use a thicker string and the note goes down. Frequency is another word for how quickly a wave travels through a string, so for us, increasing tension makes those waves travel more quickly through the fly line. The way the line tapers is also a consideration in how the wave travels through the line.

If all you take away from this thread is one thing, make it this:

We can control the tension in the rod leg after we've formed the loop.

Most of us don't try to do that, but my own casting has improved greatly since I started consciously using the rod tip after loop formation to maintain, increase or kill tension as required.

I treat the waves between the rod tip and the front of the fly leg as one sub group and the tailing loop wave as a separate subgroup, based on when they are formed in the cast and how they can be controlled after loop formation.The reason for that grouping is that I can't control anything in the fly leg after I've formed the loop. The other waves can be modified after loop formation.

The waves I can control with the tip are mends, snap casts, rod leg wiggles and the loop itself.

So, with that in mind, I'm going to start penning a few posts addressing each of the items in the list that started this thread.

Cheers,
Graeme

* Note: Dolphin noses are a special case of transverse wave included for completion. I find them more difficult to control with the rod tip after I've formed them, but I still use what I've learnt to form them on command when I want to demonstrate them.

[Graeme H]

How often is it said that slack is the enemy of efficient casting? Do we ever really question why that's so? Indeed, it forms the basis for one of the Five Essentials of casting. There is another thing that slack is the enemy of, and that is the progression of a wave through a string.

Tension is the friend of waves. Controlling tension in the string controls the wave, whether you call the wave a mend or a loop.

How does a loop morph?
The two factors controlling a wave are tension and linear mass. When we increase tension in the rod leg, we increase the speed of the wave through the line. That compresses the wave in the rod leg and at the nose of the loop, but less so in the fly leg, so the loop changes shape and gets tighter (in this scenario).

When we change the linear mass of the line we also change the shape of the loop. The long rear taper of a MED line will produce a change in the loop shape as the wave progresses through it.

Explaining the effect of "Excessive Overhang"
Waves are a transfer of energy through a medium, relying on both tension and mass. Overhang is thin line between the rod tip and the head, having reduced linear mass compared to the head of the line. When there is too much thin line, the action of moving the tip sideways does not impart energy into the thick line through the thin line. It doesn't matter if the wave were talking about is a mend or a loop in this case: too much thin line will cause the wave to fail. A mend won't hold, a loop won't open enough and an involuntary rod leg wiggle will straighten as the fly leg provides the tension at the loop.

Of course, if the aim is to have a tight loop or a straight rod leg, overhang or a length of running line is a good thing.

Increasing line carry:
Holding tension in the fly leg longer encourages the loop to travel faster and further through the line. By using the rod tip to regain tension after loop formation - either through lifting the tip or moving it slightly sideways - we can carry more line than if we we simply let the line in the rod leg sag as the loop travels away from us. I favour moving the rod tip both up and sideways, a technique I learnt by analysing videos of Christopher Rownes and Matty Howell.

Improving the efficiency of my casting:
Related to the point above, keeping the rod tip up even on short casts increases the tension in the rod leg and speeds up the loop. I need WAY less power to make any given cast now than I did a year ago and I teach my students this same technique.

My side arm casts are also much better by employing the same concept. On the presentation cast of a low side cast (where I'm trying to get a fly in under some distant snags, for example) I lift the rod tip very high as the cast progresses (after loop formation). It's bit like a reach cast all laid on its side. Pulling line up and out of the rod leg keeps the loop very tight and fast, getting it right into "letter box" openings in snag lines.

Why does the "check haul" force turn over of the cast?
This sudden increase in tension in the rod leg induces the wave to travel faster through the line. A cast that is about to fail to extend can be saved by forcing the wave to reach the fly before the line falls to the water.

Controlling underpowered curve casts:
The corollary of increasing rod leg tension to increase the wave speed through the line is reducing that tension to retard the wave's progression. When the underpowered curve cast loop reaches the desired location, pushing the rod tip forward will remove tension and make the wave stall. Here the wave is the horizontally oriented loop.

Landing aerial mends in the correct location:
Understanding that the loop is a wave helps in two ways for this skill.

Firstly, if the line has a constant linear mass (i.e. it's a level line like a DT), the progression of individual waves through it will have the same speed for a given tension in the rod leg. A loop and a mend will travel away from the caster at the same speed and stay the same distance apart. That is, if I make a mend in the rod leg when the loop is (say) 20' beyond the rod tip, the mend will stay ~20' from the loop until the loop reaches the fly. Depending on how long the line stays off the water after the leader straightens, the mend can only be 20' or less from the fly - never further from it. If we need a mend 30' from the fly, we must wait until the loop is 30' from us before making that mend.

The second way we can make use of waves is that we can kill the progression of that mend after the loop has reached the fly by reducing tension in the rod leg at that time (as we did with the underpowered curve cast). If we don't do this, the mend will keep moving away from us until the line reaches the water.

If we increase tension, we will both speed up the progression of the mend through the line and reduce its size (or even remove it completely.) That's probably not a wise thing to do if we actually want a mend.

Another way of making a mend:
The normal way of producing a mend is to move the rod tip in the desired direction and back to the "neutral" position in a lightly tensioned cast. However, by understanding how waves move through string, we can make use of the fact that a wave will reflect from the end of the string if it has enough energy and string has enough tension/mass. A fast cast with a rapid mend made immediately after loop formation will make a mend appear in the line near the leader in the opposite direction to which the rod tip is moved. (I'll have to video this one for you guys, because I expect few people to understand what I'm saying here. Oh well ... )

How does pull back work?
Pullback is the immediate application of tension in the rod leg after loop formation. That serves to tighten the wave and increase its speed through the medium.

Reducing or removing those annoying wiggles in the rod leg:
These wiggles are the result of the rod tip putting little vertical mends in the rod leg after the loop forms as the rod bounces up and down (counter-flex). Keeping the rod angle closer to vertical means the counter-flex can be used to good effect. Rather than providing annoying vertical wiggles in the rod leg, a nearly vertical rod that is counter-flexing can be used to pull the line back and tighten the loop wave (as above).

How does a snap cast work?
Pulling the medium through the wave at the same speed that the wave is progressing through the medium makes a cast in which the loop appears to travel nowhere - or at least very slowly - over the water.

So why did the loop in that vertical snap cast I made (discussed here) appear to accelerate upwards? The linear mass of the string decreases as the wave travels through the taper, so the wave speed increases.

How do front tapers work?
Related to the last point, we're reducing the linear mass gradually within the tapered section of the line. That will increase the wave speed with a given tension, so we'll see the fly leg accelerate a little at that point. I've measured the effect in videos.

Once the wave reaches the front taper, it's very difficult to stop it going all the way through to the fly. That's normally a good thing: we usually want the leader to straighten.

Understanding this is also how I came up with my hollow braid leader design. I'm ensuring a smooth progression of the wave through the system by matching reduction of the mechanical impedance of the leader and the line. It's how all leader design is done, even if we are not thinking of waves while we do it.

How can roll casts be improved using the concept of waves?
Understanding that a wave progressing from thick to thin line is going to increase wave speed, so utilising a long front taper delivers an efficient roll cast. Increasing tension in the rod leg of a roll cast enhances the progression of the wave through the string, so using pullback, keeping the rod tip high and moving it higher or sideways forces "turnover" to straighten the cast.

The 180˚ Rule:
Well, that's only half the story. It's the 360˚ Rule when we're talking about loops as waves. That is, for any regular cast, the fly lands in the same direction it came from. That's true for overhead and roll casts. For overhead casts, it just goes through two sets of 180˚.

For spey casts, we need to set the anchor in the right position first, then we just make some sort of roll cast that honours the 360˚ Rule.

When I'm teaching, it's quite easy to call it The 360˚ Rule and split it for overhead casts. Otherwise, it's one Rule to rule them all.

I'm sure I use my understanding of waves in strings more than in just these aspects, but that will do for now.

Cheers,
Graeme

[Bernd Ziesche]

Hi Graeme,
Thanks a lot for sharing all your many fine thoughts. Good stuff!
In regard of teaching fly casting to the avg. student, do you explain what casting a tight wave or an open wave means? If so, how do you explain the use of term wave for something (in my exp.) 99% of beginners already know as loops?
Thanks!
Cheers
Bernd

[Graeme H]

Hi Berndt,

No, I call it a tight or open loop. As you say, they already know the term most of the time.

That doesn't mean I don't consider the loop as a wave though, using the things I know about them to help me control the wave/loop/doll.

Cheers,
Graeme

(Doesn't matter what it's called if it does all the things a wave does when I pull its string. )

[Merlin]

For me (and I hope most people here), playing in the abstract world of physics is not an objective in and of itself. I need to be able to relate the stuff I think about to actual casting and how I might improve my own. Indeed, the whole reason for thinking about the physics is driven by that need to improve my casting - there is no other point as far as I'm concerned. I don't care at all for equations and models - there MUST be an application for it.

Agree Graeme,

I’m not after physics for physics, but for understanding with the aim of using findings for either casting or tackle design.

I don't care at all for equations and models - there MUST be an application for it.

That’s your mistake IMHO because if you make the effort of modeling you can see the intricacies behind the mechanisms you are watching at. Consequently by using the physics of the string (fixed at both end under uniform tension), you miss most of the mechanisms involved. I shall send you a paper on the principles which are applied and the corresponding equations which allow better understanding of what happens. Do you realize that you skip the effect of drag on the loop? There is also no gravity impact on the physics of the string; at least this is something in common with simplified models.

I’m not going to review all the shortcomings of your arguments, but a few which I mentioned in the loop propagation thread: the front taper does not accelerate the loop and it is not the cause of the acceleration you see in your snap cast. It is the pullback action which is responsible for that. The front taper tends to decelerate the loop because the drag forces can beat the change in momentum for a certain level of line diameter. Miss the drag, miss the conclusion. You have no clear idea of the PB mechanism which generates that acceleration with the string theory, just a best guess. If fact the string approach cannot detect the possibility for the loop to stall somehow and even slightly go back.

This phenomenon is the reason why I restarted completely my modeling, because I had a “string like” approach before. But this approach never showed a temporary stall in the loop travel, which was clearly visible on Gordy's PB videos. Once the correct equations were written and solved, then the possibility of a “stall” appeared.

Analyzing the angular momentum equation is interesting because without solving it you can understand the trends for morphing (there are other reasons linked to drag forces on the loop). Your interpretation of morphing is based on a logic which is not supported by actual mechanisms; it is again a best guess, something which looks plausible.

Finally, the string theory is based on a constant value for tension up to the top of the loop, starting from rod tip (or haul hand). But this is not true, tension varies inside the loop and this is the root cause for the mechanism of PB, snap or check. Mend is different, it is an actual transverse wave, but the loop is not. I understand your logic behind: since the loop is a transverse wave for you, then the string theory approach must apply. But this is not the case.

Merlin

[Geenomad]

Have been watching this thread and the one in the physics sub forum. Don't post there and won't get into a physics argument here in the Teaching forum but something needs to be said about where I stand to make sense of what I'm about to say.

My position on the physics of it is that I'm more interested in the predictive than the explanatory power of wave "theory". Accordingly, I think the loop is like a wave. Is it technically a wave? After agonising about it for several years and switching from yea to nay and back again a couple of times I've actually decided that is all a useless distraction from things that are useful.

Several days ago I sent an email to Graeme and here is most of it. I haven't changed my mind about it's contents and I've left out some analysis and predictions which have been supported by the evidence but again would serve no useful purpose to repeat here.

"Whole bunch of things in play here and fairly strong feelings being generated. I won’t be participating in the physics discussion in the physics subform. I’m still thinking about if and what I’ll post in response to the new thread. Oh and btw I think I finally get your view about gravity, downward movement of the two legs and loop, and (thus) upward propagation of a wave. To be fully convinced I would probably need to see space and time type measurements and how the values fit into accepted wave equations but that stuff is beyond my pay grade. In any event I have decided that that argument is one I don’t need to take a definitive side on.

As you know I have crossed the boundary into wave territory and exited again and I’ve done that on several occasions including one recently. I’m still not entirely sure where I want to take up permanent residence. However, I am sure that my uncertainty is meaningful and that it is an encouragement to explore what a wave model offers. What if, for example, instead of agonising over technical correctness I accept that fly line behaviour is in sundry respects very much like the behaviour of a medium through which waves travel. At the very least it is, as Vince said yesterday, a useful model; models being one of our inventions of patterns which help us make sense of things and save time in recognising wtf is going on. (Neuroscience is even more interesting to me than maths or physics.)

Critically, the tension of the fly line, after loop formation, (before loop formation is more the Newtonian department) can be used and changed to get helpful results. Secondly, there are things we do with fly lines, like mends, which are uncontroversially…. waves. Thirdly we can, as you have, reflect on how linear density is distributed will help or hinder our casting.

Won’t go through each of the issues you’ve thoughtfully identified and dealt with in the thread. I agree more often than I disagree and can see the value of applying a wave model or conceptual framework to understanding fly line behaviour and how we can make them behave themselves.

For all that I think you are to be congratulated. Respect."

When I go to the park to practice and improve my casting I take conceptual models and external cues with me. When I teach occasionally I might offer these to a student who seemed interested. For the purposes of learning or teaching fly casting I have no use for equations. There is one possible exception and that's because for me it is a neat, simple, shorthand account of things that do matter. Rest assured I will be trying some of the things Graeme talks about above that I haven't tried already or want to play with again.

Cheers
Mark

[John Waters]

"The front taper tends to decelerate the loop because the drag forces can beat the change in momentum for a certain level of line diameter."

Absolutely agree Daniel. A key point in making shooting head casting lines for distance casting events. For me it is a trial and error process, slow but informative.

John

[Paul Arden]

I favour moving the rod tip both up and sideways, a technique I learnt by analysing videos of Christopher Rownes and Matty Howell.

I wouldn’t. Best carry I’ve seen is Mikkel Blomberg. No deviation there. 100’ Redfish 9.5 WT line carried to the backing knot!

Cheers, Paul

[John Waters]

I must agree with Paul, I cannot see an advantage in the lift up and forward on the backcast and the lift upward and back on the forward cast, unless the back cast has sag and a loss of tension. Add speed to the line, don't truncate the stroke in order to attain tension.

John

[Graeme H]

Try it.