FW: Casting mechanics

Hi Gordy,

Would you be kind enough to ask Walter to consider this before publishing?

Stupid perhaps but I am left wondering what is being discussed. Are the “force” and its associated acceleration being considered at the rod handle or at the rod tip? If it’s at the rod handle the F=Ma is correct only for translation and is inappropriate here. Rotation is determined by torque where t=aI where a is angular acceleration and I is the moment of inertia.

In casting both are used simultaneously and in varying degrees according to style. Tangential acceleration at any point of the arc (rod tip) can be derived from the product of angular acceleration and r (radius). In the case of fly casting the radius would have to include body movement which increases this dimension to well beyond rod length and the origin of the system may well occur well outside the extremities of the casters body. So far I have ignored the fact that rods bend and that the line inertia angle relationship with the rod tip and the origin changes. If a cast started at a cord angle of 45deg to the line and finished at a cord angle of 90deg and the rod did not bend the torque would have to increase by a factor of root(2). Once the cord angle is beyond 90deg it becomes increasingly more difficult to accelerate the line. The rod handle at a 90deg cord angle of course would have travelled much further due to the flex.

I imagine that the extent of Walter’s “kick back” is dependant on the inertia of the system and the amplitude of impulse. A smooth “start up” is ideal and as Walter rightly says translation helps greatly. Not only directly but also to ensure that a practically straight line is being pulled. If the line is not straight and especially if it’s not straight close to the rod tip “kick back” is likely.

Best regards,

Ally Gowans

See my web sites http://www.letsflyfish.com and http://www.flyfish-scotland.com

2010 Spey Casting and Salmon Fishing Schools at The Kenmore Hotel June 11/13. Trout fly fishing and fly casting school "Tackling Trout" at The Kenmore Hotel May 21/22/23, 2010. See my web sites for more details of schools. Spey casting Made Easy DVD available.

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From: Gordy Hill [mailto:masterstudygroup@xxxxxxxxxxx]
Sent: 12 May 2010 17:44
To: Alastair Gowans
Subject: Casting mechanics

Alastair & Group...

From Troy Miller :

Need to think about Walter’s statement that force is constant for the majority of the stroke. In a perfect world, that sounds theoretically sound, but I believe that force will have to increase to maintain a constant acceleration during the stroke. F=mA is constant in the absence of losses. As we accelerate, the rod will encounter more drag with time (higher velocity as time progresses). So although the mass and acceleration are presumed constant, there will be an incremental force required to overcome losses.

Regards,
Troy Miller

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Troy,

Begs the question: Can acceleration continue without increase in force ?

Gordy

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More on Acceleration and "kickback" from Walter Simberski :

Gordy - some more thoughts on this.

I agree that this would be the ideal cast but it would require someone gifted with perfect coordination to achieve

it consistently. I suspect most people aren't gifted that way otherwise a lot of athletic competition

would be reduced to "who practiced the most" and "mailing in proof of time spent practicing".

If the idea that a brief transition period from zero force to full force (i.e. the ideal force for this particular cast and

equipment) makes sense to you to eliminate kick back then it also explains why adding some translation to the

start of your cast, or lengthening your casting stroke while keeping the amount of arc the same, helps to get rid of

tailing loops for some casters. We know from Bruce's work that translation contributes little to the rod tip speed

required to make a cast but I think one of the things it does is eliminate or reduce rod tip kick back and that it

is ideal for this because there is almost no possibility that I can overpower the translation movement. Using

translation I make use of my body's natural limitations to avoid kick back and save the rotation element

for moving the line in the most efficient manner.

I also think that this is why some distance casters talk about delaying rotation as long as possible. The greater

the force applied in rotation the greater the likelihood of kick back. To avoid this kick back when distance casting

add more translation before the start of rotation.

This brings up another area I find interesting - the difference in casting styles between people like Rajeff and

those using a 170 cast. We know that Rajeff uses much less translation and a greatly reduced casting arc

compared to the 170 casters and yet he consistently out performs them. This leads to endless debate

on which style is better. Perhaps the issue is not which style is better but why does one person perform

better with one style vs another style. Perhaps it has to do with early education of the caster in question where

one group is taught to use excessive translation as a short cut to overcoming the abrupt application of power

at the beginning of the stroke and the other group is encouraged to avoid excessive translation until they "get it

right", i.e. learn to use a few degrees of early rotation to avoid kick back. On the other hand it could be that

those using excessive translation don't have the attributes (e.g. coordination) required to consistently compete

using rotation only...

Bruce and I don't see eye to eye on translation and its benefits. I keep an open mind because I realize

Bruce has more experience, knowledge and capability in his little finger than I have in my whole body but I also

think Bruce is one of those people who does have very good coordination and has added many many

years of practice under incredible tutelage so he may have a hard time understanding the difficulties some of the

rest of us have. For me the shoulder injury has reinforced the fact that no matter how much I practice I will

never achieve the degree of consistency Bruce (for example) has so I look for other ways to capitalize on

my body's natural strengths and weaknesses to compensate but I also spend a lot of time comparing the

things I find to the more ideal approach just to make sure I'm not trying to rationalize why I do some things

differently.

More ramblings.... :)

Walter

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Walter,

Here is how I look at the "draggers" (Rick Hartman as a prime example) :

It is a matter of style, as you point out.

I think almost pure translation prior to a mixture of translation and rotation and finally almost pure rotation employed by those who start the cast with an element of "drag" can achieve several things including a smooth start-up (no "kick back"), elimination or reduction of slack, and the initiation of momentum.

Some casters apparently need one or all of these things. Some (lke Steve) don't.

I think you have pointed out some reasons Bruce Richards doesn't need it. To him (as you know) the primary purpose of drag when used is to take up unwanted remaining slack and so if you have no slack it is unneccesary. Bruce, however, has repeatedly pointed out that he sees many casters who improve their tight loops as they delay rotation.

Both Steve and Rick are far better distance casters than either of us. Different styles honed to perfection for each.

Perhaps I have some slack and maybe some "kick back" which I don't recognize. In any event, when I need my max distance and as perfect a loop as I can achieve, drag and the resulting delay of rotation gives it to me..... so that is when I use it.

Gordy

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From Aitor Coteron:

I was re-reading an old message and have found this comment about rod damping.

Just in case it is of interest I think that this video shows that the caster has much to do in how a rod stops vibrating:

http://www.youtube.com/watch?v=eiCKzFvrPXI&playnext_from=TL&videos=I07EeYhQEpg

Regards,

Aitor

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Aitor,

I viewed that video with interest. Looks as though the caster minimized vibration by releasing his tight grip.

I tried that with a whippy fly rod. Works even better when loaded with a fly line because some of the forces produced by the vibrating rod are absorbed by the line.

Also worked better when I did it with the tip half of the rod. Less effect when I used the entire rod. I think that may have been that with the tip section alone I was dealing with the damping of first frequency vibration whereas with the whole rod I had to contend with the second nodal frequency vibration (called the second natural frequency wiggle by Don Phillips) as well. *

Vibrating my tip half resembled the diagram in figure 9-13 of Don Phillips book taken from Spolek's work with his frequency driver. The task with the entire rod left me with the impression that superimposed upon this was the action depicted in Figure 9-14 of the same text. *

* THE TECHNOLOGY OF FLY RODS by Don Phillips, pp. 85 - 89.

Gordy

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Question from Mike Heritage:

Hi Guys,

I have missed most of this discussion and you may have already answered this, but; when we talk about acceleration I think most of us visualise the rod being accelerated by the hand from RSP to RSP. What I have read here now makes me realise that the hand stops accelerating at butt stop.

My question is, does the rod continue to accelerate after butt stop?

Mike

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Mike....

The "stop" of the hand is really rapid deceleration. Following this the rod tip is actually moving at its fastest rate during the approximately 1/10 of a second 'til RSP (rod straight position).

At RSP the loop begins to form as the line starts to overtake the rod tip.

The rod tip doesn't stop at RSP, but continues into counterflex then stops for a fraction of a second after which it bounces back as rebound while the loop matures and goes on its way.

Gordy