I have read the Common Cents articles in vol 6, #2, 3, 4 and want to make certain that I am using the proper measurement for rod length when calculating a rod’s effective Effective Rod Number (ERN). In the first article, Dr. Hanneman seems to indicate that one takes the overall rod length and divides this by 3 to determine the distance the rod tip should move when fully loaded. However, in the third article, Dr. Hanneman calculates the ERN all along the rod in one-foot segments moving away from the tip. After reading this article, I was left with the impression that the flexing area for a rod would begin at the point where the blank is held. This lead me to think that I should measure from where my hand grips the rod to the rod tip when determining rod length. This seemed to make sense since some rods have 1 to 3 inches of the blank are extended past the reel seat to form a fighting butt. Surely, the fighting butt would not be included in the calculation of rod length since this portion of the blank is not contributing to the flex. Because small changes in the value used to determine rod length have large effects on the calculation of the ERN, I would like to come up the correct value that for the distance a fully loaded rod should travel. How do I properly determine rod length for the purposes of Common Cents calculations?

Thanks,
Nils Pearson

Support the rod at a forward point that is no more than 10% of the total rod length. And be consistent. That was also mentioned in the articles although you may have missed it.

Don't include the length of any add-on fighting butt.

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Tom,
I am new to rod building and have found your magazine and website very helpful sources of information. Sorry if I asked a rather dumb question. The Common Cents system seems to hold great promise for more a accurate and objective measurement of rod characteristics. And, if I have confidence in my computation of ERN and AA, I would like to begin contributing to your database. From your response, I take it that I should measure from the point of support closest to the rod tip (which is not more than 10% of the rod's overall length) to the tip of the rod to determine rod length. I take this distance and divide it by three to come up with the distance the rod should travel when fully loaded.

Thanks for the help,
Nils Pearson

No, use the total length of the rod to derive the deflection distance from. But support it at no more than 10% of the total length from the butt. Whatever you do, just be consistent in the place where you support each blank. For instance, if your forward support on a 9' fly rod is 10 inches from the butt, then you should support all your 9' fly rods from this point. And, an 8 footer would be supported about 9 and a half inches from the butt. Make sense?

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Yes, I think I got it. Thanks for clearing that up.

Nils