About twenty years ago I started studying the mechanics of Spey casting in depth, reading all the material I could find (printed and on-line), watching loads of how-to DVDs and internet videos, and painstakingly analyzing my own casting and that of my students by means of slow motion video.
Over the years I made public some of my studies and, to my surprise, they prompted quite a few dismissing comments on fly casting forums, and, as times went by in the same fashion, I eventually removed all that material from the public view.
Now, many years and four slow motion cameras after, I have remade some of that material at the request of a fellow fly casting instructor.
Science is about constantly challenging our own views
It was Alejandro Viñuales —my fly casting mentor— who pointed me out to the fact that no matter how skilled fly casting authors were a rod in hand, most of the explanations about Spey casting mechanics were at odds with what basic Physics teaches us —and for that matter, most of the current explanations about fly casting in general, but that would be stuff for other articles.
Some ideas from the past —when our knowledge and the means to gain it were much more limited than nowadays— were being passed from one generation of anglers to the next exclusively based on the principle of authority, not giving them a second thought and checking its validity.
The very foundation of all that theoretical building about Spey casting relied in one of those wrong concepts: the “anchor” and its function as a “rod loading device”.
A misleading concept
The departure point was the misleading idea that fly casting in general works by means of loading and unloading the rod.
In overhead casting you wait for the line to unroll completely before starting the following stroke —failing to do that being a fault—, but on Spey casting the line doesn’t fully unroll, leaving only about half of it to pull on with your rod.
How to explain, then, the efficiency of the Spey technique taking that into account? Keep it simple, they said: it is the anchor on a Spey cast what helps in loading the rod compensating for that shorter line length.
Simple and simplistic are totally different things
In Physics terms rod load is based on the action/reaction, the third of the laws enunciated by Newton. In essence, that law explains that when the rod pulls on the line the latter reacts by pulling on the rod with a force of the same magnitude and opposite direction; as the rod is flexible, it gets bent due to that force.
The rod gets bent even without a line due to the inertia of its own mass, but we can leave that issue aside here. The main concept is that for the rod to get bent it must pull on the line in order to ”activate” the action/reaction mechanism.
Forces aren’t good at turning corners.
Take a one meter long piece length of string and fold it in two on top of a table, shaping a “U”; then pull on one end, does the other end move? I bet it doesn’t.
You could also take the same configuration and fix one end of the string to the table —“anchoring” it—and pull on the other end… but you won’t feel any resistance either. By pulling on the free end you don’t exert any force on the anchored end, and without a force acting on the anchor the latter can’t exert any reacting force on your fingers.
The only way of moving one end of the string by pulling on the other one is by using some sort of simple pulley, but obviously there is no pulley in a D-loop.
Looking for some visual proof?
What the following videos show is another version of the scenario described above.
Look how while the casting stroke is performed, the fluff —or the “line” tip— remain motionless on the floor. It is only after the stroke is finished that the very small tension reaching the fly leg manages to make the remaining short length of line slip backwards. Note also that at that instant when the line tip slides back, the rod is already unbending, not getting bent.
So, the force that the caster applies to the line section in the rod leg of the D-loop is not felt at the tip of the line section forming the fly leg. Even if you would tie the line tip to a ship’s anchor, the latter wouldn’t be affected by any force, and no action, no reaction.
A little experiment
Now a very simple exercise for you to feel yourself the validity of this analysis:
Rig a rod with line and leader.
Form a D-loop laying on the ground.
Hold the leader end lightly between two fingers of the line hand and make a roll cast.
Do you feel a pull in your fingers during the casting stroke?
When do you feel that pull?
Corollary
The anchor of a Spey cast doesn’t load the rod: it can not do it! The function of the anchor is a very different one.
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