Spey casting dynamics

[Traditionalist]

Furthermore, the scenarios differ depending on what you are casting and how. In the case of a line that is always inside the rod tip ( i.e. Not a head), extending line increases the mass you are trying to propel and also requires more force.

p=mv 

In the case of a mass outside the rod tip, ( a head or weight etc), which can more or less be considered a constant mass, the only variable is velocity.

The states of various things during a cast vary.  At the end of an overhead  backcast for instance, the line has no momentum at all. It is not moving, it has no velocity, and therefore no momentum.

The final momentum of the mass at the point of release is the sum of all the forces applied to it. That is also why stroke length is important, because you can apply force over a longer period of time by lengthening your stroke. You have to maintain or steadily increase line tension in order to achieve this, and this also loads the rod. The rod is loaded against the inertia of the line.

The target is to translate as much of the force you have applied as possible to the line. Which is then momentum.

Once you release the line it begins to accelerate negatively ( Slow down ).

TL
MC

[Traditionalist]

Here is a simplified calculation;

Power = Force x Velocity
Force = (1/2) x (density) x (velocity)^2 x Drag Coefficient x Area

Assume: Drag Coefficient = 0.5, velocity = 2.27 m/s, Area = 0.15m^2

Power = (1/2) x (1000 kg / m^3) x (2.27 m/s)^2 x (0.5) x (0.15 m^2) x (2.27 m/s)
Power = 438 Watts

TL
MC

[Traditionalist]

For various excellent examples and explanations;

http://www.virtualflycasting.com/Physics_FL.htm

https://www.seesar.lbl.gov/anag/staff/bono/html/ASME_Bioengineering.pdf

http://www.letsflyfish.com/fly_casting.htm

TL
MC

[Traditionalist]

There is however at least one serious error in the explanation given by Frank LoPresti. You can not "overcome inertia". Inertia is a constant property of mass.  Any given mass has the same inertia regardless of its velocity, (except at relativistic velocities). This is also why you need to continue accelerating the rod in order to maintain or increase loading and line momentum. The inertia is the same regardless of the velocity, but you have to move the rod faster in order to maintain or increase the inertial loading.

TL
MC

[Traditionalist]

Mike, if you were talking about double taper lines i might agree, the whole point of a weight forward is a fixed head weight, i can cast to around 70' using no more than by shooting the rest, as Malcolm put it 'it flies all by itself'

i see a lot of people false cast and put extra power into the delivery cast, especially when casting a bit further, the same people can't figure why they get tailing loops :lol: they also struggle beyond 70' or so because they have already overpowered the cast before they get there.

all the stuff you posted applies beyond the point where the line is comfortable reaching, this isn't distance casting its just using the profile of a wf to do what its designed to do.

i use a triangle taper mostly, it does take a bit of energy to reach 70', i also use a loop opti wf which doesn't.

It doesn't matter what line you use, or what distance you cast it, the same principles apply.

Personally I think you are confusing your own comfort zone where you can cast easily with something else entirely.

It takes energy to get anything anywhere.  You might think you are not using much but you are ALWAYS using some, and if you want to cast the same or a larger mass further then you use more.

The maths/physics also prove it conclusively. ( Although they usually wont do anybody who is trying to learn to cast much good. They are only of real interest if you want to know why something is as it is).

Anyway, you are perfectly entitled to believe whatever you wish, even if it's completely wrong, as it is in this case.

One can not shake a belief, even with proof positive to the contrary.

TL
MC

[Traditionalist]

thats for sure, I'm happy to demonstrate it and you don't believe me :lol:

lines have different profiles and people choose ones that work so i'd say it does matter, how you cast a double taper is pretty much as you suggest, progressively, a shooting head and to a lesser degree depending on the rear taper a weight forward also, you use the weight of the head to cast and shoot line to distances that would be hard or impossible to reach carrying the entire length.

basic stuff really, different line profiles are cast quite differently, the extreme being a long belly line which is carried compared to a short shooting head that is shot to the same distance, if they were not different would there even be a thread on it?

It has nothing at all to do with "not believing" you. It is nothing personal at all. I know that what you are saying is impossible based on the physical facts.  What you believe is irrelevant.

Whatever you think you would demonstrate it is most definitely not that you can cast 70 feet using the same force which you would use to cast 35 feet because I know that to be impossible.  It doesn't matter that you don't believe that or wont accept the proof offered, that does not change the facts.

Over the years I have invariably gone to considerable trouble to obtain as much information as I could about various things, not least because of my profession. As a professional engineer I could not afford to rely on beliefs, I had to have hard facts. In many cases mathematical proofs of concept based on the physics involved. Without that I could not have done my job.

Lots of people can cast well, and indeed do a lot of other things without actually knowing how it works or being able to explain it properly. It doesn't matter much as long as they are happy with whatever it is they do.

The vast majority of people don't know many of the physics aspects of casting, and it doesn't stop them doing it, some do it very well while knowing virtually nothing about it. 

However, it has always been my contention and belief that the more you know about something the better you can become at it, especially if you can practice what you know. Knowing how to do something is not at all the same thing as actually doing it. The knowledge may not be any use at all to somebody who is trying to learn how to do something, but for somebody who already can do it it allows him to improve because he knows why and how some things happen.

It makes no difference at all to me what you believe. That does not alter the facts I know to be true. But discussing things like this with somebody who will not accept basic and proven facts is a totally pointless exercise.

Your postulations are based on belief. You offer no proof at all.

Mine are based on facts with ample proof.

If you do not accept basic physics, preferring to stick to your quite obviously erroneous beliefs,  there is no sensible basis for discussion.

I am not prepared to discuss this matter any further, it is pointless, and in my experience such things do not end well.

TL
MC

[Malcolm]

I'm trying to calculate how much extra power it takes to release line with an index finger

The rosetta stone - it's obvious now!

There I was pondering whether I was reading some insight into a new Great Universal Theory penned by a new Nicolai Tesla (abetted by Lewis Carroll and Edward Lear) and it turns out you make a cast capable of 70ft and then don't let the line go and it only goes 30ft.

[Traditionalist]

You may find this of interest;

QUOTE
Summary and Cautions
Sometimes we teach casting based on what we think
is happening to the rod, line, or caster. The value of
analyzing a group of skilled casters in a study such as
this is that we can see what actually happens. This is
particularly important when one is casting for distance,
because the mechanics of a 75-foot cast require more
force and complexity than those of a 25-foot cast.
The elite casters in this study were able to store more
energy in the bent rod than the good casters and were
able to release that energy more efficiently to the fly
line. The top distance caster bent the rod the most,
stopped it the quickest, used the most body lean, had
among the best-rated backcasts, had among the wid-
est casting arcs, hauled line effectively, kept the rod
tip straight during acceleration, used weight shift and
shoulder rotation to his advantage, and benefited from
a late forceful use of elbow and wrist action. Of the
many dimensions analyzed, he had no discernible flaw.
UNQUOTE

http://fedflyfishers.org/Portals/0/Documents/Casting/MCI/Kyte-Going%20for%20Distance.Al%20Kyte%20and%20Gary%20Moran.pdf

TL
MC

[Traditionalist]

I'm trying to calculate how much extra power it takes to release line with an index finger

i don't really understand your thinking that this is just a belief of mine, i have to do this stuff in real time as a matter of course with people looking, i don't recall any of them fainting at my doing the impossible :lol:

If you stop a cast at 35 feet, it will only go thirty five feet.  If you release that cast and it goes 70 feet, that just means you have severely overpowered the 35 foot cast.

TL
MC

[Traditionalist]

The rosetta stone - it's obvious now!

There I was pondering whether I was reading some insight into a new Great Universal Theory penned by a new Nicolai Tesla (abetted by Lewis Carroll and Edward Lear) and it turns out you make a cast capable of 70ft and then don't let the line go and it only goes 30ft.

TL
MC