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Old 12-29-2011, 05:09 PM
silver creek silver creek is offline
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Default Fly rod line rating, power, and action - an explanation.

Forgive me for this long post but it is composite of multiple posts

Some recent posts about rod ratings and rod characteristics causes me to post this thread. I was going to simply post a link to where I explained the three main rod properties but it is not allowed so I thought I would post what I had written on other BBs.

The discussion was around the following video:

"The confusion about the strength of fly rods is that most fly fishers do not know the difference between the line rating of a fly rod, the power rating of a fly rod, and the fly rod action. They assume that rod power either refers to the line rating or the fly rod action with a fast action rod being a higher power rated fly rod.

What was being tested in the video was not the line rating or the fly rod action but the fly rod power. Rod Power is the ability of the fly rod to lift dead weight. It is not line rating or fly rod action. The seminal article on the difference between rod line rating, action, and power was in an interview of fly rod designers from several major companies including Seim of Sage, Steve Rajeff of GLoomis. I refer you to Fly Rod & Reel Magazine, June 2004, Vol 26, #3, pp 36-71.

You will notice that when the last rod broke, it broke in the butt. That is exactly where a properly designed progressive action fly rod should break when under a lifting load.

This illustrates the difference between casting a fly line and fighting a fish. We cast a fly line with the upper third and sometimes into the middle third of the fly rod. But we fight powerful fish with the lower third of the fly rod. Said another way, it is the butt section of a fly rod that provides the power to lift dead weight or to fight big fish. So unless you are high sticking (see the discussion of rod angle below), a rod should progressively bend and shift the load toward the butt until it fails.

With that in mind, we can see that all companies have the ability to make a powerful fly rod. It is not so much a function of the casting ability of the rod but more a function of the strength of the butt section of the fly rod. When you make a strong butt section though, you do add weight to the rod with additional hoop fibers.

While on the subject of rod power, I also think there is a misunderstanding of line rating and rod action. I read all the time that over lining a rod will turn a fast action rod into a medium action rod.

That simply is not true. Action is how the rod bends under a progressive load; it is the flex profile of the fly rod. The flex profile is designed into the fly rod and as long as the fly rod does not break, it has the same action regardless of load.

What we are changing by changing the fly line is the load. A fast action rod with a higher load is still the same fast action rod with a lighter load. It will still have the same flex profile.

All fly rods responds to the load or the work it is doing. If casting a fast 4 wt rod with a 4 wt line 45 feet requires the same load or energy as casting a 6 wt line 25 ft, why would we call the rod a fast action rod while casting a 4 wt line and a moderate action rod while casting the 6 wt line?

What changes is the timing and stroke length of the cast. So although the timing slows down and the stroke length increases with increasing loads, the action remains the same. When you hook the fish, you will still have the flex profile of a fast action fly rod with a stiffer rod tip.*

It an older post below I explained the difference between rod power and line rating. It contains some of the information above and a discussion of rod angle:

'Allow me to explain. Let's go back to the initial video of Tim Rajeff testing the power of his fly rods. Suppose that we did the same test from a bridge and we attach a weight to the end of a leader. We are substituting a weight for a fish. We want to lift the weight which is analogous to pulling a fish toward us. The rod is lifting/pulling and not casting and the this is called the power rating of the rod. Power is the ability of the rod to lift a dead weight.

The lifting power of a rod is related to the strength of the butt section of the rod, whether a fly rod, a casting rod, or a spinning rod. In the example above, if we say that the 0 degrees is horizontal to the water surface with +90 vertical being tip up and -90 vertical being butt up, any lifting angle that is positive places stress point toward the upper portion of the rod and any negative angle places the stress point toward the butt. The larger the positive angle, the stress moves more toward the tip; and the greater the negative angle, the stress moves toward the butt. Consider that if the angle is -90 with the tip down and the butt up, there is no stress on the rod at all, all of it is on the reel.

If the rod has a high power rating we can lift the weight by raising the rod above the horizontal. If the power rating is low we need to keep the lifting angle below 0. For example, we can lift the weight in increments by lifting the rod form -90 to -85, then crank the line that we have gained as we lower the angle back to -90 and then repeat the process. It would take a long time but that is because the power of the rod is low.

The taper of the rod determines how progressively the power (resistance to bending) of the rod is transferred to the butt section. Faster rods have a thicker butt section because they are stiffer and a greater taper from tip to butt. Similarly a longer rod will have a thicker butt section than a shorter rod of the same action. Since the action is determined by the taper, to make the rod longer, the taper makes the extra length of the rod at the butt end thicker.

To give a shorter rod the same lifting power of a longer rod, you need to increase the taper of the rod. So although you can design a short 7' 7" 9 weight rod to have good power, a 9 ft rod with that same degree of taper would have a higher lifting power.

Line rating is related more to the tip section rather than the butt section of the rod since the flex of the tip must balance the line for the rod to cast well. A slow rod will have a very gradual taper and this will result in a relatively low power rating for the rod - it will bend way into the butt. A fast rod will also cast the the same line but since it has a faster taper, it will have a thicker butt section that is more resistant to bending and therefore it will have more power. So two identical line rating but two different power ratings. Similarly you can two rods with the same power and different line ratings. They are both dependent on the action of the rod and the length of the rod.

I hope this explains more fully the difference between a rods line rating and power rating."


A poster then wrote, "I highly doubt most people will ever break rod at the butt like they were doing"

I replied, "I agree because most people don't know how to fight a fish. Cast the rod with the tip and middle and fight the fish with the butt. It is ignorance that makes them think you cast and can fight bigger fish with the same part of the rod.

Fact 1 - The part of the rod that breaks is that part that is overstressed. That is obvious.

Fact 2. - What is also obvious is that stress should be transferred to gradually lower on the blank where there is more "power" if you don't want your fly rod to break.

Now if you accept those two facts, a rod break in the upper portion of the rod is due either to a defect in that section of the rod such as an casting injury by being hit by something solid like a split shot or weighted nymph OR it is operator error such as a loose ferrule, high rod position, etc.

See the section on rod angle that I talked about earlier. Rod angle to the direction of pull determines where the rod stress is going to be. Now here's the thing. How many times have you heard that a heavier line rating rod can put more pressure on a fish than a lighter line rated fly rod?

Actually the truth is that both rods are limited by the breaking strength of the tippet. If you point the lighter fly rod right at the fish, you can put 80 lbs of pressure on a fish as long as the tippet is 80 lbs and the reel drag can pull 80 lbs. So rod angle determines how and where the rod stress is. It determines where the rod breaks.

As to rod breakage, we need to differentiate between longitudinal rod blank fibers that go from the butt to the tip VS the hoop fibers that are at an angle and wrap around crosswise to the longitudinal fibers. The longitudinal fibers are the 'high modulus' fibers that rod makers brag about. The hoop fibers bend around the rod so they CANNOT be as stiff unless they wrap around the rod at a very shallow angle. A higher angle gives greater hoop strength so these fibers tend to be fiberglass or lower modulus graphite. Hoop fibers prevent the rod from delaminating and exploding.

When a rod, which is a cylinder bends, the tube is deformed so that if you were to take a cross section it would not be a circle but an oval with the wide side of the oval along the inner and outer circumference of the rod blank. This stress wants to separate the longitudinal fibers and the circular hoop fibers keeps the the longitudinal fibers from separating. The longitudinal fibers are called the flag and the hoop fibers are called scrim fibers.

How Fly Rods Are Made | MidCurrent

The third part is of course the binding technology. This has really changed recently with 3M's Matrix Resin Technology.”-lines/

Here is a practical application of what I wrote above. Many years ago, I took a trip to Alaska and stayed at the Copper River Lodge.

This was before I really understood the the relationship between rod line rating, action, power.

All my friends were fans of the "new" original GLoomis GLX which was the lightest fly rod at that time. I took 2 rods, both GLX 10 footers. One was a 5 weight and the other was a 7 weight that I was thinking was going to be my go to rod with the 5 as the backup.

During the trip I never used the 7 weight and I caught big rainbows with the 5 weight without any problem.

I mentioned to Gary Borger that I never had to use the 7 weight and I never felt out gunned on those rainbows. He said that because my rod was 10 feet long, my 5 weight had the butt diameter of a 9 foot 7 weight rod. So it casted like a 5 weight, but could pressure a fish like a 7 weight. After he said that, it was obvious to me that a rod that was a foot longer would have a thicker butt section than a shorter rod of the same model and action.


"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy

Last edited by silver creek; 05-08-2015 at 09:45 AM.
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