5.FLY ROD EVALUATION AND CALIBRATION

LAST UPDATE 02/21/00 18:35

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Al Kyte, Professor

"Matching" the components of our fishing tackle Systems increases both the enjoyment and effectiveness of our fishing. Someone new to the sport may give little consideration to matching things such as the size of a fly to tippet diameter, or a flyline to a particular fly rod. In this article, we discuss the role of rod stiffness in matching a fly rod to a flyline, and then introduce a simple experiment that you can use to measure the stiffness of your rod and determine the line weight an expert would choose for your rod.

How does one determine what size flyline to use with a particular rod? A beginning angler has enough to think about already and typically welcomes the rod manufacturer's recommendation of their "5 weight"' rod to cast a 5 weight flyline. Longtime fly fishers are more likely to accept the rod makers recommended matching as a point of departure from which to experiment. The flyline that an experienced angler selects to use with a given rod may or may not match the manufacturer's recommendation.

This matching is sometimes complicated by the length of flyline (and thus line weight) an angler intends to use, the type of fishing (boat anglers sometimes overline the rod to minimize false casting as they move past attractive water), the wind conditions, and the fact that some rods seem to cast several line sizes better than others. Yet, the more we specify a particular casting distance or purpose and type of flyline (i.e shooting taper vs weight forward line), the more one size of flyline seems a little superior to any other.

But assuming we can agree to this, what characteristics determine the balancing of a line to a rod? The mass of the first 30 feet of the flyline is obviously one characteristic. But how about with the fly rod? Certainly where it flexes isn't critical; you can have a tip flexing rod and a full flexing rod that balance with the same flyline. What we have found here is that the measurable rod characteristic that is most important in proper balancing with a flyline is overall stiffness~

The American Fishing Tackle Manufacturers Association set a standard for line weights in 1961, specifying the weight for the first 30 feet of flylines, valid for all line tapers. Choosing the correct line weight for your rod gives you the ability to properly load your rod with minimum effort, and will also result in effective unloading of your rod. With effective unloading your rod works for you to propel the line forward. The forward movement and rotation of the rod butt combined with rod unloading are primary factors which control the motion of the line.

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Many of us are not expert casters and are not able to evaluate the best line weight for use with a rod. Al Kyte, longtime fly casting teacher, author, and equipment advisor has used his expertise to evaluate the line weight for use with 22 rods. Rod stiffness for these rods was measured at California Polytechnic State University. The line weight rating vs. rod stiffness data presented in Figure 1 shows a high correlation between rod stiffness and Al Kyte's line weight rating. The line weights recommended by Al Kyte often do not correspond to the line weight rating labeled on the rod, yet the line weights do correlate impressively with overall rod stiffness. The correlation shown in Figure 1 holds true regardless of rod manufacturer, rod length, rod material, or other rod characteristics.

 How can you put this information to use with your rod? If you follow the experiment described here, you can determine the stiffness of your rod and find out what size flyline an expert would select for it. Start the experiment by clamping the handle of your fly rod to a tabletop (See Figure 2). The objective is to keep the rod handle rigid when a weight is applied to the rod tip. If bending of the rod handle is observed, you may use a wedge between the handle and the tabletop. Apply a weight to the rod tip top to obtain a vertical rod tip deflection of no more than one tenth of the flexible portion of the rod. The flexible portion of your rod is the rod length exclusive of the rod handle. The floor may be used as a reference for your vertical measurements. Rod stiffness is defined as the tip weight in the units of grams, divided by the tip deflection in inches. In equation form:

Stiffness = Tip Weight(grams)/ Tip Deflection(inches) {For example if 18 grams moved the tip three inches the stiffness is  18/3 = 6 grams per inch,which would mean an eleven weight rod per the graph. You knew this but your editor did not so he is inserting this example}

If you don't have a scale to determine your tip weight, you may want to impose on the chemistry department of your local high school or college. If you use ounce tip weights, one ounce is equivalent to 28.4 grams.

We now provide an example. With your rod handle clamped to a table, the vertical distance from the rod tip to the floor may be 30 inches. Assuming you attach a one ounce weight to the rod tip, the vertical distance from the bent rod tip to the floor may now be only 22.5 inches. The tip deflection was then 7.5 inches and the stiffness of your rod is 28.4grams/7.5inches = 3.79 grams/inch. Now check to see that the deflection (7.5 inches) is less that 10% of the flexible length of the rod. Your experiment was valid if the flexible length of your rod was more than ten times the tip deflection,. or 75 inches (slightly over 6 feet) for this example; if not, repeat the experiment using a smaller tip weight. Now with the use of Figure 1 using stiffness = 3.79 grams/inch, it is recommended that you use a 9 weight line with your rod.

Figure 1 can be used to determine the line weight an expert caster would choose for your rod so that you will be able to properly load your rod with minimum effort. If you have built or repaired a rod, have a rod without a labeled line weight rating, or suspect that the line weight rating labeled on your rod is incorrect, this experiment will allow you to choose a line weight which best matches the performance characteristics of your rod. You may find that your casting ability will improve significantly when you use the line weight with your rod that is recommended by Figure 1.

(In compressing this graph we have lost a lot of detail because we don't yet know how to crop the graphic without compressing it. The horizontal scale is Stiffness(grams per inch) and the vertical scale is (Line Weight Rating [Al Kyte]) Your editor intends to ask the authors about creating a written table to go with this graph. The graph shows more nuances of  stiffness and weight than a table would but having both would be nice. The circles show the figures for the various rods tested)

Here is the table, which has been aging in my file, like good wine. Soon there will be a clearer scan of the table and a picture of the device used to develop this data.

Stiffness Range (grams/inch)                                 Recommended Line Weight

1.4 - 1.6                                                                 3

1.6 - 1.9                                                                 4

1.0 - 2.2                                                                 5

2.2 - 2.6                                                                 6

2.6 - 3.0                                                                 7

3.0 - 3.5                                                                 8

3.5 - 4.15                                                               9

4.15 - 5.0                                                               10

5.0 - 5.9                                                                 11

Rod Response

Al Kyte, Professor

Have you ever wondered why two rods with identical lengths and line weight ratings perform so differently, even with the same reel and line? Anglers sometimes refer to different "actions" of rods, but each person may have a different sense of what "action" means; the same words mean different things to different people. What most fly fishers do not realize is that there is a measurable quality that can be used to describe much of what anglers feel in a fly rod. This quality which describes a fly rod's responsiveness is its natural frequency. In this article a simple measurement is described which allows you to obtain the natural frequency of your rod.

Initially, we were skeptical to the physical meaningfulness and value of frequency to an angler. However, as we started casting rods with known frequencies, we began to understand what to look for in high versus low frequency rods. Soon we found that we could consistently predict which of two rods would have the higher frequency.

What we "feel" in the loading as well as unloading phases of the cast (the response of the rod) correlates impressively with the frequency of the rod

For the case of an unloaded rod, the natural frequency indicates how rapidly a rod responds to an input motion; it is a measure of the number of complete oscillations per second which occurs when the rod butt is moved. At a given line weight rating, rods with lighter tips have higher frequencies and correspondingly faster response. Rod frequency increases with increasing stiffness and with decreasing rod tip mass. You will be less tired at the end of the day using a rod with a lighter tip, and you will be able to throw tighter loops and cast further. Because of the faster response, high frequency rods require precise timing and may not be the best choice for a beginning angler.

Obtaining the natural frequency of your rod allows you to quantitatively describe the response of your rod. Low stiffness bamboo, fiberglas and graphite rods with heavy tips typically have natural frequencies in the 1.5 to 2.5 cycles per second (cps) range while stiff graphite rods with light tips typically have frequencies in the range of 2.5 to 3.5 cps. Rods with frequencies below 2.0 cps are considered by anglers as rods with slow response while rods with frequencies above 3.0 cps are considered as rods with fast response.

You can measure the frequency of your rod with the use of a stopwatch. Clamp the handle of your rod to a tabletop and tap the tip of the rod. The rod will vibrate at its natural frequency. Count the number of times the rod tip reaches its top most position in a given time period (seconds). This count divided by the time period for the count is the frequency of the rod (cycles per second). You will be able to obtain the frequency for rods with low or intermediate frequencies but may be unable to keep up with the count for fast rods. An equation that can be used to obtain the frequency of fly rods is presented in a paper titled "Fly Rod Response" published in the January, 1998 issue of the Journal of Sound and Vibration, available through libraries.

History has shown that frequencies of commercially available fly rods have increased with time as fly rod materials have changed from bamboo to fiberglas to graphite. We anticipate that someday manufacturers will label natural frequencies on rods which will give the consumer an indicator of rod response before purchasing the rod. If you plan to purchase a new rod and desire the same feel and response as that with one of your present rods, we recommend that you choose a new rod with the same frequency as that of your present rod.

The authors of the foregoing  two articles have kindly allowed me to post their work above. What follows is by the intrepid boy scientist who maintains this collection and cannot be blamed on anyone but him. Farther into this part of  Fly Casting Forum is some material derived from a rod manufacturer that has started labeling rod action on a somewhat different basis and there are  discussions of fly rod calibration by others, including a couple of European fly rod enthusiasts who have conducted experiments in this field. On the links page is a link to a web site maintained by Greg Spolek, another professor of mechanical engineering who has published work on rod calibration over the years.

This section will deal with methods of evaluating the capabilities of a rod by objective  means in the store or at your dining room table. The information is derived from a variety of sources, including bamboo rod builders, a man who did harmonic studies of airliner wings for a living and the literature.

1. The spring rate of a rod in engineering language, is the force per unit of deflection of a spring. The numbers I use in the data base attached to this page are the reciprocal of the spring rate - deflection per unit of force. I used a one ounce weight and measured the deflection because that is easier and gives the same information.  

2. How do you determine the vibration rate of a fly rod? Physicists call it the first harmonic - the vibration rate when the entire rod is vibrating without any node. You have all shook a rod with a loose wrist and seen it shake with a node - still spot - about a third of the way from the tip. That is not the way. In theory you could shake it at its' first harmonic with a stiff wrist but the easy way is to press the handle firmly onto a table, bench, counter top, or any other horizontal surface and start it going with a finger from the other hand. With about fifteen seconds of practice you will find that you can push it down in a rythm that will cause a substantial constant vibration that is easy to count. The harder you push on it the wider will be the arc of vibration but the frequency will not change. Push it hard enough to make the vibrations easy to count and, if you lay your watch on the counter beside the rod handle you will be able to time it all by yourself. It is not necessary to hold it and than ask someone to twang the tip. One warning, it is not easy to count the stronger rods, which will have higher vibration rates, so having an accomplice stand or sit beside the tip and count will be more accurate.

If the rods are the same length - the length from the grip to the tip top - and of comparable spring rate the vibration rate will tell you which rod will throw the heavier line or, stated another way, which rod will throw the same line farther - or - stated still another way - which rod will load more readily for short casts. The higher the frequency the stiffer the rod. Most graphite and glass rods these days have roughly similar actions so the vibration rate and the spring rate distinguish between them. The weight of the rod blank is reflected in the vibration rate. Many plug casters, who want to slow their rods down, weight the rod with lead tape or wire and make the rod slower so they get the kind of feel they want. In a plug rod you generally can cast much farther than you ever want to and accuracy is the game. So, it is easier and better to slow the rod down rather than to buy another one. A fly rod blank will have a substantially higher vibration rate than the same rod with guides and tip top installed.

Another measure of the rod's capability is tip deflection with a standard weight - I use one ounce. The deflection for the first ounce will be an indicator of the spring rate of the rod through its elastic range. In comparing rods that are labeled the same - say 7 wt., the rod with the slower vibration rate will have a greater deflection and vice versa. If one rod is markedly lighter than the other you may find a higher vibration rate with greater deflection.

With a fly rod, where range is frequently important, the frequency will tell you which of two rods, of the same length and deflection, will throw the same line farther. One thing to remember is that there are quite a few eight and nine weight rods on the market now that have a fighting butt built in. These rods generally are nine feet overall so the nine foot fighting butt rod is really an eight foot ten rod. If the two rods had the same rate the longer one would throw a heavier line or would throw the same line farther. One other thing to remember here is that just as all similarly labeled rods are not equal, all similarly labeled lines are not equal. Anyone with a cheap powder scale can prove that.

NEW STUFF

GO TO THE DATA BASE OF FLY ROD CALIBRATIONS

This is a collection of 171 fishing rods, bait and fly, that have been calibrated so far.

An example of the vibration rates of bamboo rods is below.

ROD LENGTH

---------------------7'----71/2'----8'----81/2'----9'----91/2'

150-162 ----------7wt----8-------9-----10

136-148-----------6------7-------8-----9--------10

122-134-----------5------6-------7-----8--------9------10

108-120-----------4------5-------6-----7--------8-------9

These figures are for bamboo rods, derived before the graphite era by a bamboo rod builder. We hope to post other tables by other bamboo people for comparison with the results of our measurements of the bamboo rods we encounter now. 

3, SPINE

Most people spine the rod on the soft side with the guides on the outside of the curve when you bend the rod. There are two ways to do it that I know of. One is to put the big end of the tip section of a two piece rod on a smooth surface and hold the tip end just below the tip top guide, if it has one, and roll the rod around til you find the way it wants to bend. The outside of this bend is the soft side and if you put the guides on that side, for a fly rod, the rod will be properly spined. That is also the side where you put the reel on a fly rod. For a bait rod you would spine it the same way but the revolving spool reel would go on the opposite side unless you were to spine it for a thumb on the side bait rod as many bait target casters do. But that is a different subject. These people cast plugs with the guides and the reel seat turned 90 degrees to the spine of the rod. It is the predominant position for journeyman bait casters. They thumb the side of the spool rather than the line in the middle of the spool.

Another way to spine a blank is to simply put the butt on the floor with the rod vertical and push down on the tip. It will bow out to the softest side, once again with the soft side being the outside of the bend. This is the way factory rod wrappers do it I am told.There is no tip top on the rod yet.

If you are acquiring a rod and/or calibrating it it is a good idea to spine it. I had the pleasure of re wrapping the top sections of four or five rods that were spined at ninety degrees. The theory of spining is that the rod tip will trail true on the forward cast if you spine on the soft side. You can check this out by trying to bend the rod from the soft side or from the opposite side, the hard side. The rod doesn't want to flex straight on the hard side but will try to bend sideways whereas on the soft side it follows the line of least resistance and bends straight and in line. At least one of the high end manufacturers states in its literature that its rods are not spined and that its engineers say spining is not necessary. Preliminary results of your sampling of new rods shows that maybe a quarter of them are spined on the soft side. Some people spine the rod by twanging it and seeing which way it vibrates the straightest. They then use that plane as the spine - that is, the guides will be placed on the side of the blank that represents the tip of the oval path of the vibrating rod tip.

Aside from its' effect on the tracking of the fly rod, the spine is significant in evaluating the  action of the rod when you hang a weight on it. It is well to compare the  action in the same spine plane.

I spine only the tip section of a two piece rod. With three and four piece rods it would be the top two sections. It gets a little dicey with these rods because you can be assured that, in a finished factory rod, the manufacturer put the rod together in such a way as to wind up with a straight rod, irrespective of the spine. With the big push to four piece pack rods for jet set travelers spining is more complex, if it is done at all. As a practical manner, if you put it together so it is straight and then spine the top two sections on a four piece it will be as good as you can expect. It is possible to experiment with the sections in the event that they can be made straight in more than one position. If that is the case try to use the configuration that has the least spine - that is closest to having no spine at all.

ORVIS FEATURES CALIBRATED ROD ACTION RATINGS

Orvis has trotted out its' new "Flex Index" a system for assigning number values to the tip action to butt actions spectrum of rod actions. Orvis describes it this way:

To establish a rod's flex action the rod is placed under a constant flex - it's bent- and the ratio of the portion of the rod on either side of the apex of the flex point is determined. That ratio, minus 1, is multiplied by ten to get the rod's Flex Index. The slower the rod, the closer the flex point is to the butt and the lower the Flex Index. The faster the rod, the closer the flex point is to the tip and the higher the flex index. These numbers range from 2.5 to 12.5 by 0.5 steps. Slower rods-full flex - have numbers from 2.5 to 5.5, moderate - mid flex-6.0-9.0 and fast - tip flex- 9.5 - 12.5. Orvis cautions that these numbers refer only to the flex action of the rod and are independent of the designated line weight for the rod.

As examples, a particular model in 5 wt, medium action has a Flex Index of 7.0. That flex can be duplicated in an eight weight of a different model. Evidently the Flex Index of each model is the same and different weights in the same series will have similar flex indices.

Orvis has not copyrighted this system and wants the industry to adopt it as an industry standard - much like the line numbering system I imagine.  An industry wide way of rating the comparative power and action of fly rods would be a boon to us poor consumers.

I have no need for an Orvis rod right now but would be pleased to receive comment and data on this new development from those among you who are getting Orvis rods or already have some. It would be interesting to vibrate the rods and determine if rods marked for similar line weights and similar flex indices have similar vibration and spring rates. Or, if similar flex weights in different line weights have different  rates. This seems like a step in the right direction.

15 DEGREES SPEED METHOD OF ROD RATING

Ludwig Reim and Theo Matschwewsky have extensively researched fly rods and have determined that the average cast of 12 to 18 meters of line will bend the rod tip to a fifteen degree angle. In order to simulate this condition they have learned to fix the rod horizontally in a vice and pre bend the rod with the weight of the line. The rod is then bent further to reach 15 degrees and released. The time needed to reach horizontal is measured by electronic means and this time is then converted to meters per second. This speed is then applied to the action length of the rod to give a speed factor for the rod. Up to 1.6 is a slow rod, 1.7 to 2.2 is medium fast and over 2.2 is fast.This description has been supplied by Sven Ostermann, of Germany. We hope to provide some example figures shortly, received from Ludwig and Theo.

Ludwig and Theo have evaluated some rods for us to see so look this over and see what you think.

ROD TEST "15 DEGREES SPEED METHOD"

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Copyright 1999 BP Ptrs.

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