Tag Archives: acceleration

Loop Control Paradox (divertimento for curious casters)

Loop width control is a recurrent topic in casting instruction. Several aspects govern loop width, but “matching casting arc to rod bend” is what instructors use the most; so “if your loops are too wide narrow your casting arc” is the usual fix we offer.

Let’s say that I am bass fishing with a popper knotted to a short, stout leader, followed by a bass taper #7 weight line. I want to cover a very promising spot, just a small hole among low hanging branches, which asks for a side cast with a narrow loop.
First try my line crashes against a branch: I need to narrow the loop considerably. So keeping everything equal I decrease my stroke angle… and the loop fails to straighten, for same acceleration along a smaller angle gives, obviously, less line speed.

So keeping the same stroke angle I increase the force applied to the rod to gain that lost line speed. But, hold on one second! More force applied results in more rod bend, and a basic principle of casting mechanics says that we have to match casting arc to rod load! So this time I must increase the stroke angle! Now I widen the angle applying more force at the same time… and my popper curves to the left hooking a branch, as a result of an overpowered cast.

Reducing casting stroke angle to narrow your loops doesn’t work in isolation. No wonder that beginners have a hard time in controlling loop width, as it is a question of very fine-tuned adjustments, more than just varying “casting arc”.

Playing with loops by changing the casting stroke angle is fine; play with force and stroke length as well just to see what happens.

Focus Shift

Nowhere in the world of sending a fly out there with a line you can find rod load being more glorified than in the spey casting scene. Everything seems to gravitate around that. If the cast is good it is because the rod was properly loaded. If it went wrong… well, sure it is due to the rod not having enough load or unloading prematurely.

Sometimes it is possible to get more clues from the analysis of a bad cast than from a perfect one. That is the case with the casts depicted here. The video and pics show a pretty common occurrence that will be used to point out some keys of spey casting mechanics. Take them just as a brief introduction to following articles which will get deeper into that subject (slow motion clips and some not-that-heavy-physics included).

The scenario is the forward cast of a spey characterized by some kind of V-Loop that we will call 7-Loop (thanks to Simon Gawesworth). An extreme 7 for that matter.

Let’s say that you set a nice V-Loop, make the cast and present the fly on target.
On the next cast you manage to get a 7-Loop and the fly falls short of the target on top of a heap of line and leader. That is just one of the possible outcomes of that loop configuration -as it is a fat loop, a tailing loop or even the three of them combined-  if the caster doesn’t compensate his stroke to adapt. Even if he modifies his stroke successfully the 7-Loop is still inefficient due to the amount of wasted energy.

The following gif made from a couple of pics from a still camera will shed some additional light.

7loop-problems

We could look for an explanation to the inefficiency of that 7-Loop in the gif above in the usual way, basing our analysis in the behaviour showed by the rod. It would go along the following lines.

What happened to this cast?

  • Hmm, probably the rod didn’t get loaded… but I see a pretty good bend, though!
  • However, is that a properly loaded rod? Who knows? I, for one, don’t have a clue nor have met anybody capable of quantifying whether a given load is enough for a given cast or not. If only because you can make a cast to the same distance with the same rod and line with rather different loads.
  • Well -you say to yourself- it could be that the rod got unloaded prematurely due to the anchor slipping… but the loop’s rod leg looks pretty straight, whereas the rising tip of an early unloading would have set a wave in it!
    As shown here:

Hmm, we are not getting very far with that approach.

So let’s address the issue from a different standpoint, forgetting the rod and putting the accent in the line.

From the gif above we can quickly draw some visual clues:

  • A totally ineffective anchor due to the angle of attack.
    Only part of the leader is in contact with the water, moreover the angle at which the loop pulls on the anchor makes the latter specially prone to slipping. See how at the end of the stroke the apex of the loop still hasn’t moved forward due to the slipping anchor! In fact it moves a little bit backward! It is a perfect case of a loop propagating but not traveling (but that will be the subject of another article).
  • The amount of line in the rod leg of the 7-Loop.
    The length of line in the rod leg at the start of the stroke is very very short. The longer the piece of line we propel during the casting stroke (the “live line” so to speak) the more efficient the cast:

The reason for that inefficiency has already been covered in this previous article. You can also relate it to the case when we rush the forward stroke of an overhead cast and start it with the line still half its way backwards.

So, compared to a proper V-Loop configuration, for presenting the fly at the same distance a 7-Loop:

  • Will ask for a higher rod butt acceleration, as a way to give enough momentum to the comparatively shorter length of “live line” we propel during the stroke, to carry a comparatively longer length of “dead line”. That is the reason why the  “dead line” to “live line” ratio is key regarding efficiency: the longer the live line the better.
  • Anchor slipping wastes energy: the line moving backwards goes in the opposite direction of the target, and it doesn’t move by itself so it detracts from the energy needed to move the line forward.

Obviously the longer the cast the higher the impulse you need, which may result in a bigger load, but load is a byproduct of our force application to give the line enough momentum. It really isn’t our goal.

Given that the function of the casting stroke is to give enough velocity to the line in the right direction, it is better then to shift our focus from the rod -which says very little- to the line -which speaks volumes.

Why is a Jump Roll More Efficient than a Static One?

That is a rather usual question and also a very interesting one. It has been asked to me again recently via the internet by a couple of fellow casting instructors. Let’s go for it.

Let’s take a look first at the Roll vs. Overhead video used in a previous article:

I will describe the scenario:
Just one rod rigged with two lines: Royal Wulff #7 and Rio Tournament #6.
The TT has the ideal taper for roll casting; the Rio is designed for long casts overhead.
The Rio is unrolled behind the caster; the TT set in a roll cast configuration with its leader anchored by means of a screwdriver stuck in the ground (is there a more solid anchor than planet Earth itself? If there is let me know).

In this way the very same casting stroke applies force to both lines. What the video shows, however, is that the overhead line reaches its target whereas the rolled one falls short. It is an interesting experiment that any caster can try by himself (just in case somebody doubts of the result).
Anyway the result is that, if you use a stroke with the amount of energy needed for the overhead line just to straighten, the roll cast line falls short of the target. Always. Why?

I have said that the very same casting stroke applies force to both lines simultaneously, but is it the same amount of force for both? No, it isn’t.
What our stroke is doing is applying the same acceleration to the rod, and the rod to both lines, but the length of line actually accelerated in one case is much longer than in the other: we accelerate the whole length of the overhead line whereas only a short piece of the roll line is subjected to acceleration.

Do you remember the basic formula of Force?
F = m.a.
For a refresher this is a nice and easy source Force

Acceleration is the same for both lines but mass isn’t. So the force we apply to the roll cast line is much less than that we apply to the overhead line. For the same, identical, casting stroke getting the same distance with much less force sounds impossible, right?

If you prefer we can address the problem from the standpoint of Energy.
By applying force to the lines over a given distance we are doing Work on them. Do you remember the formula for Work?
W = F.d
For a refresher this is a nice and easy source Work

The work done on an object amounts to the energy transferred to it; that is, more Work = more Energy transferred.
But we have already discovered that the roll line has been subjected to less force than the overhead one; less force amounts to less work done on the roll line and, consequently, less energy in it.
How do you expect to get the same distance with less energy?

So what we have is that the casting stroke that works for an overhead cast isn’t good for a roll cast. By the same token the stroke good for a jump roll isn’t enough for a static roll.

Some may say that, after all, that rod load shown in the video is just enough for propelling one line but not both. Another of the blindfolds that the casting paradigm based in load puts over our eyes.
Yes, only one line is propelled all the way forward but, how is it that it is always the one with the longer piece of “live line”?

So, as a corollary, IMO we have to think in terms of how long is the piece of line I am accelerating directly to the target, and not of the mythical “load” and “anchor loading” or the impossibility of a “highly energized V loop”.

Addendum

The key to understand this issue lies in the fact that the rod in the video isn’t applying the same force to both lines, just the same acceleration. It seems that it isn’t easy to grasp so an additional (more graphic) example to clarify this is in order:

Let’s say I have a video showing three model railway coaches.
Two are connected together and laying on a straight rail. Parallel to them there is another rail with the third coach laying on it.

In the front part of both convoys we have a string, one string for each convoy.
At a given time the strings get taught and the two convoys start moving with exactly the same acceleration.

Since the track has a ruler alongside, by means of Tracker or any other application we are able of easily calculate the magnitude of that acceleration.

We also know the respective masses of each convoy: isn’t a surprise that mass A has a value X and mass B has a value of X/2.

By solving the F = m.a equation we get that the force applied to mass A is double the force applied to mass B. Right?

Well, after that first video I show you a second one with a general view of the scene. Now we can see that there is a guy pulling on both convoys at once by holding both strings in one hand.
So now, out of a sudden, we discover that he is applying the same force to both convoys? Not al all, the force exerted on each of them is different, one being exactly half the value of the other.

Mysterious Creature Rides Again

Tailing loops. So frequent and still so puzzling.

As I wrote on the first post in this series we already have a pretty good idea of how tails are formed; getting rid of them is another matter entirely. I truly admire the insights of instructors from yesterday: reaching the conclusion that tailing loops come from a concave tip path of the rod tip wouldn’t come easily, specially if we take into account that there wasn’t high speed video available at the time. Today’s technology effortlessly shows that, in fact, it is a dip/rise of the rod tip what creates the dreaded tail. And this evidence renews my admiration for the amazing observation skills of those pioneers of casting studies, for although that dip/rise is somewhat a “concave path of the rod tip” it has nothing to do with those big bowl shaped tip paths so many drawings depict. For years those bowl shaped explanations were to me as perplexing as the tailing loops themselves: however much I looked whenever I saw a tail in someone’s casting I couldn’t see that big concave path everybody was writing about. Not even on the casting videos available. Reality is much much more subtle, so subtle that seeing with the naked eye the expected anomaly in the tip path -even knowing what to look for- is really hard. Here we have a tailing loop in full glory. It is played at a slower pace than real speed. The tail could be used to illustrate a casting handbook; can you see the “bowled rod tip” anywhere?: Tailing loop backcast a bit slower than real Better to use a gif at 100 frames per second, that is 1/4 of the actual speed: Tailing loop backcast slow Observe how even at a pace three times slower than reality we just can catch a glimpse of some anomaly in the tip path. So let’s use a visual aid to see what is exactly happening with the rod tip: Tailing loop path This has cleared things up a little bit. Mainly two things come to my mind. First is that to get a tailing loop, even a huge one like that shown above, you only need to mess up a relatively short piece of the casting stroke. Second is a consequence of the previous observation and my main point so far: that this problem is so recurring due to the fact that a very small error, for just an instant, results in a surprinsingly big effect. It isn’t easy to feel, and then correct, things that happen in an instant, is it? It isn’t easy to detect for the caster himself nor for anyone else. The tailing loop depicted above is really huge. Let’s watch carefully another good one of more moderate size. Can you detect where in the stroke does the error happens even in slow motion? I can’t. The only way is playing the original video frame by frame to discover a veeery subtle dip and rise of the rod tip: Tailing loop backcast small tail Dip/Rise of the rod tip. It is worth to emphasize the “Rise” part since that motion is key in the formation of the transverse wave in the fly leg that we commonly call tailing loop. But that, together with some considerations about what is the ultimate cause of tails, is the stuff for a next article. P.S. The tailing loops shown here are real ones, nothing staged for the camera but involuntarily produced. The caster is a really fine one who drove from 400 km away for a course to improve his technique (I felt flattered and, at the same time, worried: would I deliver as expected?) His hauled casts were really nice. Then I took the camera and asked him to cast with the rod hand only. Removing the haul wreaks havoc with line control, but it is a fantastic exercise to educate our rod hand.

Mysterious Creature

Mysterious creature

Tailing loops have the aura of a mysterious creature. Currently we know pretty well how they are formed but, at the same time, we can’t help to surprise ourselves when we get a tail now and then, no matter how experienced we are.

When casting for perfect loop control I will immediately detect any error in the stroke, my hand will easily feel any deviation from its intended straight line trajectory. The view of the fly leg getting out of plane in relation to the rod leg at the latest stages of the loop life does nothing but confirm what I already knew before stopping the rod: that I had messed up the stroke tracing.

Next cast I drive the rod butt straight but fail in accelerating it progressively. Now, though, I am only conscious of my fault when the dreaded tailing loop appears in the line; I don’t feel any clue in my hand. The mystery lies in the fact that the most subtle error in force application may result in a noticeable tail. An error as subtle that we can’t even feel it. The cast shown below is a good example of that.

tailing fast

What’s is the nature of that error in applying force? Just a spike in acceleration somewhere in the middle of the stroke. If the rate of acceleration decreases before reaching the end of the stroke the tip of the rod rises over its previous path; it is that rising what produces the transverse wave that we call tailing loop. Nothing mysterious but somewhat hard to grasp for some casters.

The main issue contributing to this confusion is the lack of differentiation between the concepts of velocity and acceleration and their respective roles in rod loading.

High rod speed doesn’t necessarily means big rod load. Load is a consequence of force, and force isn’t related to speed but to the rate of change of that speed, that is, to acceleration. Let’s take a simple view to that.

Let’s imagine that, at a given instant during the stroke, we have a rod butt speed value of 6 units, and in the previous instant the speed value was also 6 units. Rod butt speed is constant, no acceleration.

On another cast at a given instant the rod butt speed is just 5 units and in the previous instant the speed was 4 units. It has increased its speed from 4 to 5 units, that is, it has accelerated during that period time.

So we have a cast with a rod butt speed of 6 units against a cast with a rod butt speed of 5 units. Guess what? At that point in time the cast with the slower rod speed will show a bigger rod load!

This is a somewhat simplistic approach since there are other aspects at play which affect rod loading, such as air drag and angle between line and rod butt, but it is accurate enough to illustrate what we are dealing with.

We also know that any premature unloading will make the tip rise over its previous path creating the wave which will evolve into a tail. For the rod to unload the force applied to it must decrease. And here comes the fundamental part to understand this issue:
We don’t need to stop the rod to unload it; we don’t even need to decrease the speed applied to the rod for it to experiment some unloading!

Let’s imagine a casting stroke whose speed increases progressively. The rod butt speed profile measured at successive instants could be like this:

2, 4, 6, 8

This shows that the speed is increasing in a progressive way, accelerating at a rate of 2 units of speed per unit of time.

But then we measure the rod butt speed at the next two instants and find that its progression has changed:

2, 4, 6, 8, 9, 10

Speed continues increasing but acceleration has decreased from 2 units of speed per unit of time to only 1.

Remember that force is directly proportional to acceleration so a decrease in acceleration equals a decrease in force: the rod unloads correspondingly.

This is what has been traditionally called non-smooth, non-progressive or erratic acceleration of the rod. This is what gets our tailing loops flowing. And, IMHO, this is the reason why tailing loop formation is so subtle and difficult to feel.

One more apparent mystery with tails: when made on purpose even a casual glance to high speed video clearly shows that their alleged cause very rarely matches the real one. Even with pro casters. This leads to the idea that those long lists of tail-producing problems are just part of the story; they aren’t causes of tails by themselves, they just might be conducive to tailing loops… if you aren’t good enough at force application.

Tails, so easy to make when you don’t control and so hard to purposefully produce when you have refined your skills! So difficult in fact that even terrible timing or creeping usually fail to get the expected bad result when our force application is spot on.

In practice, the only real cause of tailing loops is a faulty acceleration, or a casting angle too narrow to accommodate the bend in the rod. In my experience the latter is much more common in casting instructors demos than in real life.

Now let’s make some analysis of the cast shown here.

Obvious thing number one: the forward cast starts toooo soon.

If we don’t wait for the line to straighten we are walking in dangerous terrain: we are not necessarily getting a tailing loop but we are conjuring it up.

So when the line straightens while the forward stroke is in progress the weight of the whole line shocks the rod and produces the tail, right?

Well, no, that is an explanation from the times when casters didn’t have the tools to check what is actually happening. As the gif above shows the hint of a wave in the line which will turn into a tail appears way before the backcast gets straight.

What makes a rushed timing more prone to tailing loops is much more subtle.

The cast shown here, with that early start of the stroke, accelerates just part of the line. By the time the loop is formed there is still line getting incorporated to the forward cast adding more weight to the launched line. This obviously decreases line speed. So to compensate for that lost line speed the bad timed cast must launch the line with a higher speed than in the case of a proper cast with the line fully straightened back. For the same stroke length and angle that implies necessarily a higher acceleration. In layman’s terms you must cast “faster”, and fast motion and control don’t come along very well. Conversely, going “slow” and smoothly increasing speed are a perfect matching pair.

Obvious thing number two: lack of hauling on the forward cast.

What helps enormously in getting control of the rod hand is… the line hand. Let’s get a little deeper into this.

To send the line and fly to a given distance we need to propel it with the required minimum speed. We can get that speed by the use of the rod hand only, or, by means of a haul, we can add extra speed to the line making the task of the rod hand easier: it doesn’t need to apply the same rate of acceleration, going “slower” with the rod hand is now enough to get the necessary line speed to reach the target. And by going “slow” it is much easier to get the proper progressive acceleration we are looking for.

In my view an efficient haul could have avoided the tailing loop even with the fault in timing present.

What are your views?

Double Hauling Musings

Silueta

Lately I’ve been thinking about the approach to double hauling from the mainstream instructing standpoint. To be honest that hauling is somewhat considered an advanced technique leaves me scratching my head. When I was a child I broke one of the pedals of my bicycle and it took some days till my father fixed it. Did I stop riding the bike during that time? Come on! Are you kidding? It wasn’t very pleasant but, at least, it was still cycling anyway; when eventually the pedal was back in his place… What a difference!

Having two hands you should employ the same logic you apply to your feet: using both isn’t an advanced technique, it is a basic one! That, once learned, hauling is always used (whatever the distance we are fishing at) seems to mean something, doesn’t it? So, in that regard, leaving for later the learning of a fundamental technique for efficient casting looks debatable. Specially because in the case of a lot of fly fishers that “later” actually means “never”. And they can’t be blamed for that. In fact those to be blamed are casting instructors themselves, not only for delaying addressing that task but also for a poor understanding of the function of hauling.

This is the logical route followed by many anglers: They say that hauling is for giving speed to the line; but I only fish small to medium streams, I don’t need to cast far… so learning how to haul doesn’t interest me. Quite logical reasoning if you ask me, when what you have heard about the function of hauling is just increasing line speed. Of course hauling actually accelerates the line, and it is a fundamental tool for distance due to that. However the main goal of hauling is a more comprehensive one, something that applies to every cast whatever the distance: Increasing our overall control of the cast. Just try this by yourself: make some casts at around15 meters with the narrowest loops you can get by using just the rod hand; then try the same by adding the line hand: hauling narrows the loop significantly. Think of that prime lie under those long low hanging branches and we are talking control now.

Moreover (and here comes the capital aspect of this control issue contained in the act of pulling with the line hand) underneath any activity involving motor skills lies a fundamental truth: the faster we perform a motion the harder it is to keep it under control. For the same line speed the portion of that speed provided by the haul allows for a slower, less accelerated, more relaxed motion of the rod hand. Rod hand motion sets trajectory and shape of the loop; any error in tracking or force application is going to have a bad effect in line behavior (and regarding force application even the smallest error is going to have a big effect). A rod moved with a relatively slow motion can be much better and easier “driven” than a faster one.

Conversely moving the line hand fast doesn’t pose the same problems due to the line being guided by the rings. The only serious risk is a tailing loop due to the haul ending too early in the stroke, and that isn’t very common.

OK, you say, but every instructor is aware of the utmost importance of double hauling, and this technique is a basic aspect of every teaching program, so this is just some byzantine discussion of interest only to some casting geeks. Well, not in my opinion. The issue has much more implications than it seems at first sight, because this popular attachment of hauling to “line speed” as an absolute —and its consequent exclusive link to distance casting— has had a profound effect in how the technique is taught.

In terms of timing and length of the haul all the instruction we receive is intended at getting maximum distance, but not at allowing a greater control at the most usual trout fishing distances. And since these two different goals also require —I think— different technical approaches it is the time to get a little deeper in the nuances of hauling. I for one have changed the way in which I teach the double haul.