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.