ERL (Effective Rod Length)

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Hi Gordy,

I would mostly agree with Ally if ERL (effective rod lenght) would be the length of the cord going from the hand to the rod tip.

However, if we employ the definition by Don Phillips (that contradicts the previous definition by Marinaro as explained on my yesterady's attachment) we have that the ideal straight line path (SLP) of the rod tip that we encourage in our students means that the ERL doesn't change during the cast. We all know that a perfect SLP is not possible and that in an actual cast the rod tip path draws a somewhat convex shape. Doesn't that shape mean that the ERL is actually increasing during the stroke?

On the other hand the concept of effective lever arm length doesn't demand the lever to be flexible. If we cast with a broomstick the ERL will vary during the cast, first increasing and then decreasing.

The link of a high speed video cast by Grunde that I sent the other day was to prove that point. And that's the reason for my disagreement with Walter about the issue of ERL decreasing during the cast. The discrepancy lies in the fact that I use the definition of ERL by Phillips as shown in the attached file.

Regards,

Aitor

P.S. I find this kind of discussions very enlightening, however I understand that other members may see them as utterly boring. My apologies to them.

(I placed Aitor's attachment of Don Phillips' diagram with this message........ G.)

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From Eric Cook :

Hi Gordy,R

Unfortunately, I have yet to have the chance to read "In the Ring of the Rise" and have only previously seen the definition of effective rod length from Phillips. It is one that I have accepted. From seeing the picture of the text from Aitor, I would suggest that Marinaro's definition of the chord length to be no more than a geometric description. It would be of little or no use for mechanical study (Not to say that there is no use for it at all). Whereas Phillips definition of being the moment arm (perpendicular to the direction of the fly line) is valuable information for study.

You asked the question; "Would the same rod with different cast demonstrate different ERL's?" Yes it would, according to Phillip's moment arm definition. In fact, if you where to take two cast that were identical in every way with the exception of trajectory of the line, the ERL would be different. Let's say you had those two identical (acceleration, stroke etc.) cast and changed the trajectory by 15deg in either direction (up or down, thinking 2 dimensional here) the ERL would change by about 3-1/2". See my attached crude sketch. If any one is skeptical about this it can easily be proven out in CAD or if you wish one can attempt to measure statically.

Eric

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Eric.... I placed your diagram of the CASTING MOMENT ARM in an attachment. Gordy

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