I hope all is well. I have some data on static load deflection curves for fly rods now and have a few wonderings. Of course most will come back to “cast the rod with different lines and see how it feels,” but I am still interested in this.
You know the “Common Cents” system uses a single point on the static load deflection curve (load to deflect 1/3 rod length) and uses that load to establish an “Effective Rod Number” (ERN). Many people have many opinions of this. Some say is absolute (ie ERN=ELN and an ERN of 5 should use a 5wt line), some say it is relative (for comparing different rods and you normally like line to be 1 or 2 above or below ERN), and some say it is garbage.
Of course all of this came about because fly line wts are standardized (ie the first 30 feet of a 5wt line is 140 grains +/- 6 grains) but fly rod weights are not. One manufacturer 7wt may be the same another’s 6wt or 5wt.
I have established the entire static load deflection curve for 10 rods (not all mine). Various wts, lengths, materials. I have removed all manufacturer’s names, but classify by length and marked weight and graphite or fiberglass. Below my code is 8-5 f is an 8’ rod, 5wt, fiberglass. 10-5 g is a 10’ rod, 5wt, graphite. You see there is lengths from 6.5 feet to 10 feet and line weights from 3 to 8 right now and half are graphite and half are fiberglass. Obviously there are some random errors but I think the trends are illustrative.
In figure 1, there is just the raw data. Load (measured in pennies) and deflection (measured in cm). In figure 2, the rod length is “normalized” by having deflection as % of rod length vs load (pennies). In figure 3, both are normalized. Same normalization for deflection, and the load is normalized for EACH rod, normalized to the load to deflect that rod 1/3.
You can clearly see in figure 3 that “all fly rods act like fly rods.” If a rod deviated from the trend, it probably would not be a good fly rod.
My couple wonderings. You see in figure 1 AND figure 2 that the “9-8 g” and the “9-7 g” are very similar rods. Makes sense. They are both actually about 9.5 ERN, and behave very similar on the graphs. Different manufacturers, but one marked 8wt and one marked 7wt. Seems they should both be marked the same with a standardized system. BUT, in figure 1 (no normalization), you also see that “9-5 g” and “10-5 g” seem to be similar. BUT, in figure 2 (deflection normalized), you see that “8-5 f” and “9-5 g” seem to be similar. Is one of the figures better to show similarities? Curves with actual data overlapping or curves with normalized data overlapping. My guess is the first (actual data overlapping) because when you normalize both the load and the deflection, then all the rods look similar to each other.
My second and more important wondering. If someone believes the common cents ERN (either absolute or relative), then would it be possible (better) to find percent deflection from a COMMON load? Instead of finding the load that makes a COMMON percent deflection. In my mind, then if you had that load (mass of 20 pennies or 30 pennies as in figure 2), then you could use that common load, determine what percent of the rod length it deflects the rod, and then have a “industry standard” that would make the fly rod weight scale the same across the board for all. You could also take that load to a fly rod shop and quickly do that test and determine if it is the “right weight” rod you are looking to buy.
Figures below.
Figure 1:
Figure 2:
Figure 3: