Fly casting physics....paradox

Hi Gordy,

Actually, I see SLP as having multiple implications on casting. The
first can be summed up as "line follows rod tip" as you've described

Another aspect is that for the most efficient of transfer of energy
to the line the rod tip must follow a straight line path. I
recall that in a former life you were a spear chucker on your track
team. As someone who was a very poor javelin thrower I used to wonder
why people who were weaker and slower and had what I considered
poorer style could throw a javelin farther than I could. I realize now that
part of the answer is slp. Since we didn't have a javelin coach to
explain this I expect that the people who were able to throw the
javelin farther probably had an instinctive understanding that if their
throwing hand moved in a straight line path then the javelin could be
thrown farther with less effort. The same principle applies to casting.
One of the Loop articles I wrote talks about this and had some pretty
cool math to show how much energy is lost if the rod tip moves in
an arc rather than a slp.

Well, all that energy isn't going to help us much as we cast if that perfect SLP with absolutely no convexity of the rod tip path results in the line crashing into the rod tip. Works fine with the javelin, becsause there is no rod tip and no line. G.

Bruce's previous message about rod bend vs acceleration is a good one.
I hope nobody minds if I paraphrase but in more physics like terms:

Force = mass times acceleration

more acceleration is equivalent to more force

Rod bend is a measure of the force being applied to the rod, so:

more force = more bend and conversely more bend = more force

and:

no force = no bend

no force = no acceleration (this could be everything is at a dead
stop OR moving at constant velocity)

no bend = no acceleration (more correctly no external forces since
we know gravity can also bend the rod)

Very clear. Now: how do we calculate the WORK involved ? We should be able to calculate it and define it in dynes or ergs. G.

Now to add some things from Server's paper:

The bend in the rod can be used to determine the direction in which
force is being applied.

A uniform bend in the rod indicates that force has been applied in
one direction only. A non uniform bend can result if forces are first
applied in one direction and then quickly in another direction (this
would look like a wave in the rod if we had a stop action camera to
view this).

Now to capture what a number of people have said:

We don't see waves in the rod when viewed in slow motion so we
know that there are no sudden direction changes in the way force is
applied during the cast. What we do see is that the rod first bends
or flexes in one direction, then it straightens smoothly, then it
counterflexes (i.e. bends in the opposite direction). So what must be
happening is force is applied smoothly in one direction (causing flex),
then is smoothly reduced to zero (causing the rod straighten smoothly),
then force is applied smoothly in the opposite direction (resulting
in counterflex and stoppage of the forward motion of the rod).

If that force, applied by the caster, in the opposite direction CAUSES counterflex, then it must initiated PRIOR to counterflex, as I see it. Since counterflex occurs after RSP by definition, then that force must be applied prior to RSP.... which is what we've been teaching all along. G.

Now two more points from Server's paper regarding the stop:

1. So what we typically think of as the stop - the action that causes the rod
to straighten or unload - does not involve applying force in the opposite
direction, it involves reducing the force we are applying with our hand
to zero. As a result the rod stops accelerating, since it is no longer
accelerating it straightens even though our hand is still moving forward
and we haven't applied force in the opposite direction yet. Now the rod
counterflexes so this is the point in time when we are actually applying
force in the opposite direction. So physically stopping the rod (i.e.
applying force to stop the forward motion of the rod) happens after the
rod has unloaded.

2. This is why the "stopless" or 170 or elliptical cast or Sexyloops cast works
when there is no physical application of force to stop or unload the rod.
The unloading occurs when forward acceleration comes to zero even though
there is no physical action taken "stop" the rod. Every action on the part of
the caster up to the point of rod unloading is expressly taken to maximize
the forward velocity of the rod tip (and hence the line).

And finally (again from Server's paper):

In effect there is no such thing as a stopping action during the cast that
causes the rod to unload. What we think of as the stop (applying force in the
opposite direction) occurs after the rod has already unloaded.

Walter..... That is the part which defies common logic. It makes no sense to me at all. Apparently Bruce Richards agrees. If you can embrace this concept, then tell me just what it is that the caster does to initiate rod unloading. G.

And finally my two cents:

I've done my best to state what I think Server has written about. If
my interpretation is wrong then the fault lies on my side. Server and I are
planning to have some discussions about his paper this week. If I have erred
I will let you know but I will expect that actual clarification of what Server
is saying will come in an update of the paper by Server.

Cheers!

Walter

I love this stuff ! Exercised my brain. Gordy

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I plan to make an attempt at a MCI designation in Loveland this year. I am not an engineer and I am not a physicist. I am a student of fly casting. I read every group message that I receive from you and I absorb what I am capable of. Sometimes I am confused, sometimes I am enlightened.

I have come to the conclusion that as part of being a successfull instructor I must be able to eliminate the confusion and strive for enlightenment for any students that I teach. There is an amazing wealth of knowledge in this group and the information that is supplied here is more than enough to provide that "enlightenment". If it is the "physics" of the cast or just "tried and true" teaching methods or a combination of both that make the student understand then it is a success. After all is said and done we just want happy students and instructors.

We are providing this fascinating physics of fly casting mainly for background information. No examiner will expect you to know the details as you take your MCCI exam. We've gone way beyond what is required.

What is required is a distillation of all this physics down to what makes good sense as your basic understanding of fly casting mechanics. Not the formulae, the calculations or the differences in our expert's opinions.

Attached please note a message which I sent to a Master candidate who was a salt water fly fisherman. This chap was concerned over the amount of math which might be required during testing.

This is my answer to one of our Group members who is a big game salt water fly fishing expert (FFF CCI ) about to take the MCCI exam next month.

My answer addresses his concern over the amount of mathematics needed to pass this test in view of the various formule and equations which have appeared in our many Group messages over the past few years.

Also addressed, is his concern over the fact that he uses heavy salt water tackle on an almost daily basis, but will be taking the exam with the designated equipment (7 wt. system or lower.)

# The "rule of elevens" : (subtracting the X number of the tippet from 11 and bring it to the thousanths place for the diameter of the material)

# The "rule of nines" : (Subtracting the X number of the tippet from 9 to get the approximate pound strength of the material.)

# The "rule of fours ( or threes)" : To approximate the size of your tippet to the hook size of your fly, divide the hook size by either 4 or 3 .

# Loop speed related to fly (top) leg and rod (bottom) leg speed : Add the speed of the fly leg to that of the rod leg and divide it in half:-

Since you are primarily a salt water fly fisherman (as I am) I'd not expect you to use the formalae above very often. As a true Master, however, you need to know how to advise your students who ask you about fly tackle for trout fishing in the mountains, etc.

Some rough, "rules of thumb" for salt water leader material are probably already familiar to you:- (Even so, I doubt you will be asked this.) These are some approximations which, of course, will vary with different nylons and brands.

You already know that fly lines are rated by the grain weight of the first thirty feet regardless of design and excepting some shooting heads. Only tiny bit of, "math" to consider is that for most lines, every time you subtract 5 to 6 feet by carrying that much less line as you cast you are casting with one Wt. less line.

As you carry more line while casting than the first 30 feet, every time you add 5 to 6 feet you are really casting with one additional weight line.

The detailed calculus equations which have appeared in some of the past Group messages over the past few years are strictly the product of physics research of casting parameters. They have no place whatsoever in teaching students fly casting and, therefore, will NOT appear during your exam !

In the short time you have before your Sept. exam, you should do all the tasks on the exam many times over while striving for perfection each time. Best to do these with the outfit you will be using at test time.

Going, as you are, from the daily use of heavy salt water tackle to the 7 wt. and a tiny yarn fly will be less of a problem if you keep practicing to perform the tasks with only the minimum power needed. Some of these tasks require polishing your, "tip casting" techniques so rarely used in the salt.