Translation / Rotation ... Clarification

 

Walter & Group................

 

Great teaching trick from Joe Libeu: -

 

Oval, tension or Belgain cast in teaching the pick up and lay down or false cast. 

 At times when I have a student that has timing problems and getting the feel of the cast I will have them work on the oval cast or tension cast.  I will start them with pulling the rod in a low side arm back cast and then move to a more vertical position on the fwd cast.  As the understand and feel this cast,  I will get them to move the side arm back cast up towards a more vertical position.  I keep moving the side are cast up until it becomes vertical.  This seems so work with most people as they can feel the tension and rod load on the entire cast.  Give it a try.

Joe Libeu
Sierra Pacific Fishing Adventures
310-749-6771

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This is another great example of a teaching use for the, "belgian cast." 

 

It beats the trick of using a fly line a couble of wts. heavier than the rod for the student to get the feel of the rod load, because you don't have to rig up new equipment.

 

Gordy

 

 

 

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Peter Minnick asked for more clarification on translation & rotation :-

 

Peter...

 

Actually, you have it right.

 

Translational phase =  The, "pulling" of the fly line in the direction of the cast with no change in rod angle, prior to the rotation of the rod which yields an angular change in the position of the butt section of the rod.

 

The rotational phase yields the greatest tip travel and line speed.  This is because a small angular change at the hand yields a large change in tip travel on account of the long lever arm provided by the fly rod.

 

Ongoing discussion centers on whether the translational phase mainly is used to take up slack on the back cast or whether it contributes by overcoming the inertia of the fly line and, "starting the ball rolling" by gaining rod tip speed to some degree prior to the rotational phase, thus making the rotational phase more effective.

 

Some rod loading occurs during the earlier translational phase, but most happens during the rotational phase.

 

Ideally, the rod tip path should remain a straight line during both the translational phase and the rotational phase of the cast.  The change is from linear (straight or non angular) path of the butt section of the rod to an angular change in the position of the rod butt.  For most casters, there is a gray area where the translational phase blends with the rotational phase. 

 

Different casters and different casts will use varying amounts of translational and rotational phases.  For most casts, there is a blend of the two, as I see it.

 

Bruce Richards has noted that having the caster delay the rotational phase until later in the stroke often improves loop control.  That fits well with the concept of, "start slow and end fast".

 

A crude way of describing it is, " Pull the line forward, then rotate the rod".

 

Acceleration of the rod tip occurs through both phases.

 

Acceleration at the hand level, as I see it, is a very complicated amalgam of earlier linear acceleration giving way to principally angular acceleration.  I don't know if this has been quantified.

 

Gordy

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 Thanks Gordy.... that's a crystal clear description. I suggest you share it with the group.  Peter

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Comments and casting video by Jeff Wagner.  Note the early translation quickly going in to rotational phase with a blend of the two prior to full rotation near the end of his stroke:-

 

I was copied this by Gordy, I hope you dont mind if I give a few pieces of

information that I think might help. I agree with Bruce about constant

rotational acceleration and have attached a diagram (look at the third page,

the video to match can be seen at http://dhflyfishing.com/video.html) of my

hand path during a distance cast of 124' using an Echo Comptition series

distance rod with a 5wt 120' XXD line, not that the distance is important but

it gives good background information. I do agree that translational movement

could be greatly decreased with perfect loops. I think you will notice that

from the very begining of the stroke the hand path is downward and continues

through to the wrist rotation (followed by a slight thrust). This

shows almost

constant rotation, much like acceleration, starting with slower

rotation at the

beginning and steadily increasing the rotation rate to a very rapid

deceleration

and follow through.

Th early translational movement that is seen is from imperfectons in

loop shape

and removing slack. Which is deleterious to the cast and would improve the

distance if it were eliminated, a pursuit that seems to have no end!

--

Jeff Wagner

Master Certified Fly Casting Instructor

Fly Fishing Guide, Jax Outdoor Gear and Kirks Fly Shop

Fly Fishing Buyer, Jax Outdoor Gear

Redington Pro Staff

Colorado Angling and Casting Club (ACA), President

PH: 970-481-5887

Web: www.dhflyfishing.com

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Walter Simberski on my comments re smooth, constant acceleration:

Gordy,

 

That would mean that once any slack has been taken up the bend in the rod remains constant throughout the stroke...

 

Walter

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Walter......

 

I had to ponder that for a while.  I wonder if counteracting the inertia of the fly line wouldn't bend the rod more even if acceleration of the rod tip remains the same (???????????)   Also, perhaps some, "skin drag" ?

 

A lot to learn, here.

 

Did you ever get your LOOP article written ?

 

Another question I can't answer:   If you have acceleration at a given rate, say x ft./sec./sec, and you increase this to, say x + 5 feet /sec/sec, what would you call this ?    ..... ? increased rate of acceleration? ..... My (apparently misguided), "accelerated acceleration ?  ....? greater acceleration ? ....  seems there must be a term to describe this.

 

I wonder if this is what goes on when the space shuttle is launched..... or is this, "constant acceleration" with an unchanging rate ?

 

Gordy

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Hey Gordy!

 

Once the slack was taken out of the line the bend in the rod would be directly related to the acceleration. If the acceleration is constant then the rod bend should stay the same.

Since the force is equal to mass times acceleration (F = m x a), and the mass and acceleration are constant, then the force is constant so the bend should stay the same. There

will be a minor increase in resistance due to skin drag as the speed/velocity increase but it would be negligible.

 

 

I've also been running an Instruction for Instructors course which has been a great experience. Even more fun than teaching beginners. I have a couple of guides and people who

have been doing instruction so the discussion has been excellent. I'm learning as much as I'm teaching.

 

There are a number of expressions that could be used to describe an acceleration which isn't constant. Mathematicians might talk about a non zero third order derivative. Physicists

would probably call it time dependent or time varying acceleration. Accelerated acceleration would also be an acceptable term but this would imply a constant accelerated acceleration,

e.g. acceleration at time t would be defined by an equation of the form a(t) = mt + b where m and b are constants.

 

The shuttle would be time dependent acceleration at launch. Basically they fire up the rockets and they are full on from the time they are started to the time the fuel is exhausted so the force

remains constant BUT the mass of the shuttle decreases significantly due to the burnt off fuel so the acceleration increases. In space a short rocket burn would be considered constant

acceleration (or very close to it) because the change in mass with retro rockets is relatively small.

 

I'm looking forward to having more time available to get back to some of our discussions.

 

Cheers

 

Walter