Question - DAMPING

Walter & Group...

[GH]  Answers to Mike Heritage's question on damping :

"Sound job Mac, the only one I find any real issue with is

Damping Action-  A term that refers to how quickly a rod recovers to a resting position at the end of rod motion. Rods that dampen quickly are generally more desirable (also referred to as dampen).

 

That definition would be to do with the rods frequency. I have always understood the term damping to be something the caster does (relax the grip, for instance) that dampens out any frequency occilation that may send secondary waves down the rod leg."

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[GH]  Mac Brown answers, directly :

Hi Gordy, 

This is an answer for Mike's question on dampen.  I usually teach that the only time we squeeze the grip is at the stop, hence we naturally dampen. Mike, perhaps it needs a second definition for relaxing the hand after the stop of the rod butt for some styles.This does help a bit in minimizing the counterflex and recovery. I hear it used more in terms of rod attributes so I guess that is why I describe dampen this way. 

I am in the process of getting up my old rod studies from the mid 90's. In those studies, we had a spring deflection test for 55 fly rods to measure this term "dampen". The rods that had the quickest recovery (dampening) after deflection were due to the makeup of the rods construction (usually these are most expensive as well). Moment of inertia of the rod, distribution of mass (want the tip section lighter), stiffness, hoop diameter (if you double diameter it increases its strength roughly 16X), rod frequency, modulus used, resins, and the list goes on. 

I am sure that most people have picked up rods to cast that would be better suited hanging from the wall at some Cracker Barrel Restaurant. Part of this is because after you stop, the rod has many counterflex and rebounds due to poor rod design. You can relax the hand after the casting stroke and it still feels like a giant catapult going back and forth for quite a while (these are rare now with all of the improvements). Catapult types of action dampen poorly. Will get a link to rod study on the page in the next week that will explain rod attributes with data. 

Best, Mac

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[GH]  The very clearest writing I could find on damping, is that of Don Phillips in his TECHNOLOGY OF FLY RODS. *

From his GLOSSARY OF TECHNICAL TERMS :

Damping, aerodynamic : Damping caused by air friction.

Damping, force : Damping caused by friction, either internal material friction or externally applied friction.

Damping Factor :  The numerical ratio of damping in a given system to the damping in a fully damed system.

From his text :

"DAMPING.   

Any real vibrating system is subject to damping, or decay of vibration amplitude, in the absence of any external applied forces.  Note that the correct term is damping, not dampening.  Dampening occurs when you drop your fly rod into the water.  Without damping, vibration systems would continue to vibrate indefinitely, without any decay in amplitude.  Damping has always been of interest to fly- fishers, since it mitigates undesirable rod tip oscillations at the termination of the rearward and forward casting strokes. The causes of damping are many, but they tend to group themselves into four principal areas; aerodynamic, external friction, internal material friction and external applied forces.  'for fly-casting, drag on the rod tip and line, friction of the line in the guides and in the ferrules, internal friction between the fibers and resin and compensating forces exerted by the angler's hand. "

* THE TECHNOLOGY OF FLY RODS by Don Phillips, 2000, pp. 88, 99.

Gordy