Just the tip?

[Few]

Trigger warning: This may be the most basic question possible about casting physics, so I'm relying on the reader's forebearance. Does the trajectory of the rod's tip during the cast (meaning rod tip position in three dimensions vs. time) completely determine the resulting cast? To avoid distractions I'm assuming there is no hauling, and the line starts out straight, without slack, in an idealized back cast (am I forgetting anything?). If not, what are the other parameters that matter?

To make the question more concrete, if the same section of line were cast by different rods, or by caster's with different strokes, but they somehow manage to create precisely the same sequence of tip positions vs. time, does an identical cast result? If a casting machine were built that includes no rod, but nonetheless precisely duplicates the tip's trajectory, would it too create the same loop?

In short, are all the rotations, translations, accelerations, forces, twists, steps, loadings, stops, hits, etc. just a complex set of underlying motions that yield a tip trajectory? Or do those underlying details directly affect the resulting cast independent of their effect on the tip? Of course some motions might make achieving the desired tip trajectory easier than other motions, but I mean to set that (admittedly important) aspect aside for the moment.

Why am I asking? in part, because I find the question inherently interesting, but also because changing what I visualize while casting has an effect on the result. Moving away from focusing on loading and unloading the rod yielded far fewer tailing loops, for example. If when and how the wrist is rotated matters beyond its effect on the tip's trajectory, I want to take that into account when assessing my casting. But if it all really comes down to the tip's trajectory, I need to adjust my mindset a bit.

Few

[Graeme H]

Does the trajectory of the rod's tip during the cast completely determine the resulting cast?

Trigger warning …

Yes.

But also after the loop has formed.

Cheers, Graeme

[Few]

Thanks for the response.

Few

[Few]

Sorry...after the "the stop," tip motions cause line disturbances that counterpropagate back toward the fly, correct?

Also, I saw the thread you started regarding the role of line tension in determining the rate of wave propagation. I have to admit that issue had completely escaped me.

Few

[John Waters]

If when and how the wrist is rotated matters beyond its effect on the tip's trajectory, I want to take that into account when assessing my casting. But if it all really comes down to the tip's trajectory, I need to adjust my mindset a bit.

Few

Hi Matt,

IMHO, the wrist patterning and sequencing does matter beyond impacting the tip's trajectory, it determines tip speed and all tip speed impacts. There is a difference as the line lengthens. I must admit to a degree of indifference in respect of waves travelling down the rod leg.

John

[Paul Arden]

avoid distractions I'm assuming…., and the line starts out straight,

This is a significant part of how the fly leg will behave, but if you assume it to be identical then tip path is what matters.

Cheers, Paul

[Graeme H]

Sorry...after the "the stop," tip motions cause line disturbances that counterpropagate back toward the fly, correct?

Also, I saw the thread you started regarding the role of line tension in determining the rate of wave propagation. I have to admit that issue had completely escaped me.

Few

I would not say “counterpropogates”. It’s just another wave traveling from the tip along the line towards the fly, like all the others that happen during the cast. A tail also travels from the tip to the fly.

But yes, every movement of the tip affects the line during the cast, from the time it begins moving in one direction to the time it stops moving in that direction.

Cheers, Graeme

[VGB]

I must admit to a degree of indifference in respect of waves travelling down the rod leg.

Maybe if presentation casts were included in competition, you wouldn’t be indifferent?

After the stop, they propagate towards the loop but don’t go around it.

Vince

[Bernd Ziesche]

Does the trajectory of the rod's tip during the cast completely determine the resulting cast?

Trigger warning …

Yes.

Hello Graeme,
My answer is no.
Tip path is one aspect.
Relation (angle) tip path to the (unrolled) line is another huge aspect.
Then tip speed is another aspect.
Line length is another aspect.
Shape of the unrolled line (if unrolled) is yet another aspect.
Line density and line taper are 2 more aspects.
Line weight is an aspect.
Wind is another aspect.
Fly resistance is another aspect.
How about trajectory relative to the shape of tip path?

The more slomos I watched, the smaller tip path became in its impact as a stand alone key factor for the resulting loop.
Regards
Bernd

[Paul Arden]

They propagate at the speed of the loop.