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.

5 comments on “Loop Control Paradox (divertimento for curious casters)

  1. mark says:

    Couldn’t agree more…had this very discussion just this morning.


    • Aitor says:

      Glad to see that we are on the same page. Probably we modify stroke angle and applied force to get the needed line speed, then adjust loop width via stroke length.


  2. stoatstail50 says:

    Couldn’t agree more…had this conversation just this morning.

    I don’t think I have ever seen anyone casting or instructing who actively matches Arc to Bend to achieve a particular tip path…(although quite a lot of people believe that they do). Tip paths and tip velocities are not produced by a strictly binary relationship between Arc and Bend.

    Rotation, Force and Translation, in the form of the Hand Path, all contribute in varying measure.

    For me, Arc and Stroke Length are just terms for the measurements of the angle through which the rod has been rotated and the rectilinear distance the rod has been translated. Translation can be curvilinear as well as rectilinear, hand paths are frequently curvilinear.

    Bend is a byproduct of the material properties of the rod and the net forces applied to it.

    There is definitely a relationship between bend and arc but they are not the only controllable inputs that mediate the behaviour of the tip. We have both cast a rod that doesn’t bend and achieved close to SLP with a very tight loop…this isn’t done by matching arc to bend because there’s no bend, changing something else made this tip path possible…. or maybe it just happened by magic.



  3. Staffan Dahlbom says:

    Interesting stuff, I had a couple of “soon to be instructors” over this weekend and as we were working us trough the performance test we had a long discussion about task 19.

    [Task19: Teach an intermediate caster the adjustments needed to maintain loop control when
    changing distance from 30 feet to 50 feet, and the reasons for those adjustments.]

    The intention, I guess, is to explain the ajustments needed in force, as well as in casting arc. (Covered in expectations A and D).

    The relationship between mass (or acceleration) and arc is quite simple (As you write Aitor)
    The relationship between mass (or acceleration) and force is also simple.

    More mass the wider the arc, more mass the more force you need.

    But to study this in real casting situations (as the complex phenomenon it is) is something else.

    I’d say Open up your casting arc will give you a longer force over distance (longer SLP). It will also give you “shorter” rod and less speed with the same but rotation. Same but rotation with a heavier line calls for more force. More force and longer tip travel is more work onto the line. //I could go on loosing myself//

    Could opening the casting arc (and hence gaining distance, and work done to the line) be enough, no added force that is?

    Could lengthen the translational motion (not opening up the arc) and not adding force be enough?

    My conclusion is, the adjustments that has to be done as you lenghten the line, may vary (from one cast to another, and from one caster to another). Most likely it is a successful mix of both arc, force and stroke length. And the differences are so tiny (in terms of centimeters or degrees or newtons), that they become hard to notice for the human eye.



    • Aitor says:

      Hi Staffan,

      I agree with your conclusion. In my view we adjust stroke length and angle to give the line the necessary speed to reach the target, the farther we want our fly to go the mire we increase the elements of our casting stroke.
      I find that traditionally stroke length has been underestimated, for it is as important as angle regarding line speed. Mots of the force we apply goes into rotating the rod, but since work is F x D, line speed depends on torque as much as on the distance over which we apply that torque. In this regard it is possible to increase the casting distance without increasing the force; from a different standpoint it is possible to cast longer without increasing rod bend.


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