Shane's clarification on casting mechanics

Your lengthy explanation helps me understand better what both you and Server have stated. All should read this.....those who don't want to go in to detail should at least read your last paragraph.

Your point about the word, "linear" is a good one. Of course, it means, "in a straight line". This, however, could be used to mean literally in a straight line, or it could mean a straight line graph such as might be seen of a graphic representation of a measured parameter such as force, velocity, or acceleration.

Lastly, your detailed message was NOT a, "diatribe" which is, "mean spirited". One might call it an informative expostulation !

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(To Gordy and Group from Shane)

I am responding to Server's comments on what I had written before. He does make some valid points and I appreciate his comments and chance to clarify. This dialog is what our group is all about. I still think most of what I said is correct, yet a couple of points were imprecise or misleading the way I stated them. "Gendanken Experiments" can be very insightful, but without quantitative data, it is insufficient and often imprecise. I would still like to see more quantitative data. It helps us think things through visually, however.

Following are corrections/clarifications/comments in Blue to misleading statements in Red. (Note also that there are more than one use of linear that could lead to confusion. So I'll try to clarify):

As Bruce Richards points out, per results from the casting analyzer, expert casters exhibit the best results with a linear acceleration of the rod butt (rotational acceleration). [Really, its not only linear it is a near constant rate of acceleration. This is can be seen in the nearly constant slope of the velocity plot against time as the rod is loaded by an expert]. This is what we mean by smooth application of power -- linear [constant] acceleration of the rod [butt]. This is unlike a less adept caster that tends to have a non-linear application of power (and speed) during the stroke, often overcompensating at the end of the cast or an erratic application of power through the cast. The casting analyzer gives us good experimental evidence of what is happening at the rod butt. But what is happening at the rod tip?

Of course assuming the rod tip is traveling in a [nearly] straight line (through balanced arc length and power application), the rod is converting angular (rotational) acceleration to linear [I meant here, straight line as opposed to angular] acceleration of the rod tip. In essence this is a mechanical amplifier, amplifying the rotational movement of the hand, rod butt, and rod to linear velocity of the the rod tip and fly line.

Here is a Gedanken Experiment (as Einstein called thought-based scenarios) If the rod did not flex at all (a broomstick) the rod tip would accelerate (angular) at the same rate as the rod butt [at a near constant rate]. (Ignore translational movement of the rod butt.) But we know the rod is a flexible lever and bends as the rod is accelerated (we must accelerate to bend the rod). [When we accelerate the rod butt during the stroke some of the energy goes into the kinetic energy of the rod and some into the potential energy (load) of the rod.] When the rod bends from linear [constant] acceleration of the rod butt, the rod tip necessarily lags behind a straight rod position due to inertia. If we accelerate continually and smoothly, it will continue to lag more, deepening the bend [yes, this be comes harder and harder], until the rod butt is rapidly decelerated (at the stop). Therefore the rod tip starts moving at a slower speed and is accelerating slower than the rod butt. Although accelerating, it continues to travel slower than the rod butt and accelerates slightly slower until it the rod butt stops. At this point the rod unflexes continuing to accelerate (quite rapidly at the end) to the RSP. [This was imprecise and a slightly misleading statement, in that as a mechanical spring, the greatest acceleration is when the spring is at greatest load and is initially released to unload. In theory, it is continuing to accelerate to the RSP (velocity is still increasing), but the rate of acceleration decreases linearly with respect to position (until acceleration is 0 at RSP, or the resting point of a spring.] The [rotational] acceleration of the rod tip is over the same arc length (ignoring counterflex), but over a slightly longer period of time (~0.1 s) [according to Bruce and Nolan]. Therefore, I think the rod tip is starting out a slower rate of acceleration early [during rod loading] and ending at a higher rate of acceleration [upon unloading, begins greatly accelerating but at a decreasing rate of acceleration] and moving very rapidly (higher velocity) at the end (ultimately we are after line speed, right.) [As with any spring, the acceleration will reach 0 and the velocity at maximum at RSP] According to Bruce and Nolan's results, the loading of the rod approximately doubles the velocity over a straight non-flexing stick. I think this is an increasing rate (non-linear) of acceleration (straight line) of the rod tip, despite the linear rotational acceleration of the hand. But it may still look very smooth.

I add: another way to look at this is there are two phases in the cast. The first phase is the loading - we accelerate the rod to bend it as deeply as we can (or as necessary). The second phase is the unloading by decelerating or stopping the rod hand. As the rod begins to unload it is at its maximum acceleration. This drives another point: How fast the rod is loaded is ultimately not relevant to how deeply it is loaded. We could bend it back by slowly pulling the tip and holding it (like a bow and arrow cast). When we are casting normally, though, it just so happens that we bend it by accelerating the rod butt and the tip against the inertia of the line. But like an archery bow, it is not how fast we pull the bow back, just how deeply we pull it. [how fast we do it really relates to the velocity of the rod tip imparted by the casting stroke. ]

The main point I was originally trying to make is that the acceleration of the rod tip over the total cast (both phases combined) is not at a constant linear acceleration. Is this better? I think it is still largely true, but hopefully more correctly stated. Hopefully it isn't more confusing and that this, now lengthy, diatribe contributes to better understanding. It has helped me.

Shane