I'd like to tap in the knowledge base of the forum
I did some extensive search in the archives about rod sensitivity, and I must say that the results do not yield a very clear picture, at least for me.
There are for instance some persistent assertions about guide numbers or guide height that are clearly not or ill grounded.

As far as I understand the issue, sensitivity of a rod is the rod's ability to transmit to the fisherman's hand variations in the line's tension.
If I got correctly Tom's point in several of his posts, the rod's ability to do that is related to its stiffness/weight ratio, which I think is more or less equivalent to my prefered version: stiffness/moment of inertia ratio (S/MoI).
In other words, all else being equal, the stiffer the more sensitive. And all else being equal, the less inert the rod, the more sensitive.

I prefer the moment of inertia over the weight since it takes into account the distribution of the weight, which is essential. going from cork to burl on a standard spinning will probably cost you 10g extra, but I doubt it will make much of a difference with respect to sensitivity.
Changing running guides from BLAG6 to Minima 4 will probably not make 3g difference (Eric?) but WILL make a measurable difference in sensitivity.

Are there important aspects of the topic that cannot be reduced to a S/MoI consequence?
thanks for sharing some understanding.

_______________________________________________
If I'm not going to catch anything, then I'd rather not catch anything on flies.

Prostaff Rodhouse
[www.rodhouse.fr]

Laurent,

I will normally NEVER respond with this answer but a search utilizing all dates will reveal the information that you seek.

It's the stiffness to weight ratio that's important. Not just stiffness alone.

...........................

Get the disc or back issues with Emory Harry's articles. He goes from engineereze to humaneze about as well as it can be done.

There is at least one mistake in that article IMO. The author says that for the same weight, the more limber or softer rod will be more sensitive. That has not been my experience on the water. Just my .02.

Laurent,
I think that the best thing to say about rod sensitivity is that it is best to say NOTHING.

Rod sensitivity can certainly have a million different definitions to a million different people.

I think that a better thing to say, is that one should always build as light as possible to maximize any potential that exist in a particular blank for a given application and leave it at that.


Enjoy the best rod that you can build with the blanks and materials that you want for the build.
Then, have you and your client enjoy the rod to its fullest capability.

Spencer,
Thank you for the compliment but Ken is correct. I am not very proud of that article now. In the years since it was written I have learned a good deal more about how a fishing rod transmits an impulse or vibration and that article has at least two errors and in at least one area it is very over simplified. It turns out that how a rod transmits an impulse or vibration can be very complex but I think that at present the biggest problem with sensitivity is that there is no agreed upon definition. It seems to me that until we have an agreed upon definition an accurate description is virtually impossible.

Laurent,
Look this one over


[rodbuilding.org]

I know this is a can of worms. But generally lighter the better for a particular power/rigidity. Yes, so high power to weight ratio. But also balance. Great balance allows the hand to be relaxed and just cradle the rod lightly which I believe increases sensitivity of the sensors in one's fingertips and hand.

Mo

thanks everyone for the imput.

Thomas : as stated, I began with the search, but the problem wasn't the lack of answers, rather an overflow of inconsistant info

Tom : yes, as stated, the central notion is stiffness/weight, or (my preference) stiffness/MoI

Spencer/Emory/Eugene: thanks for the references, I'll check them asap

Roger: I agree with your diagnostic but I have doubts about the cure. Claims about sensitivity and the ways to achieve it are all over the place, and clearly play an important role in marketing as well as in the way people think about their own experience with tackle.
I personally think this is a fascinating theme, and one that concerns more the spinning/casting community. Some of the relevant parameters (the main ones?) describing a fly rod have received, and still recieve, serious attention by scientifically minded people. Sensitivity/resonance deserves the same.

Mo: thanks! a very insightful comment.

Emory: Bill Hanemann started by giving a definition for the terms, together with a story about why he thought the definitions were useful. I've not read your paper yet, but let me say that you don't need to find a consensual definition before starting to work. The work itself will show the usefulness of the definitions. At least that's what the CCS example clearly shows.

My hope in starting this discussion was to locate existing efforts in this direction, and maybe contribute to motivate others. I think that we could learn a lot about our rods, just in the way we learned a lot about action and power thanks to Bill and the discussions the CCS triggered.

_______________________________________________
If I'm not going to catch anything, then I'd rather not catch anything on flies.

Prostaff Rodhouse
[www.rodhouse.fr]

Laurent,

My appologies for overlooking the text stating you had already done the search! I was in no way trying to be condesending or sarcastic.

Tom

Laurent,

This is probably a dead topic already but would like to add that while stiffness/MoI is important, it does not explain entirely impulse transmission. For instance I have two rods of same power, action, and build yet I can feel better with the lower modulus rod versus the higher modulus rod. It just leads me to conclude that there is something else to the impulse transmission equation that we are missing here. Possibly there are some confounding variables that are leading me to this being a false conclusion. Any idea to what they are? Also, I would be very interested in hearing what Mr. Harris has learned since his article on rod impulse transmission regardless of agreed upon definition or not.

Best Regards,

Craig

This should be very interesting, because very few understand that the "moment of inertia" is a property of a particulat geometric cross section, perhaps a hollow circle. It is not dependent upon any properties of the material in question. That is to say that the moment of inertia of a hollow carbon fiber tube (fishing rod) is the same as the moment of inertia of a hollow steel tube of the same dimensions.

Laurent,
As Emory and others have stated, the significant issue when discussing fishing rod sensitivity is how and what is needed for such a measurement and or definition.

Then, you take the case where for many folks, fishing is done on a slack line. If you have 5-10 feet of slack line floating on the water, where does the word rod sensitivity come into play - for a particular fisherman on a fine fishing morning?
Pretty tough for any thing that happens at the end of 5 feet of slack line to be felt by any one at the end of that line and that person holding that rod at the end of that slack line.

I think that is why it is as or even more important that a rod be able to remain 100% alert throughout the entire day of fishing. This is where like balanced rods, light rods and similar items come into play.

If a person fishes a long day and only has two or three bites in a day, it is very important that the person holding the rod, be just as alert at the end of a 15 hour fishing day, as at the beginning of that day. If that person only gets two or three bites in a long day of fishing, it is so important for that person to be alert so that he/she does not miss that fish - no matter the time of the day.

If you want to call it rod sensitivity that helps - great.
If you want to call it light weight rod, so be it.
If you want to call it balanced rod, great.

But, all of these factors make a particular fishing rod successful for a long day on the water - even when the number of bites is poor on a given day.

Be safe and just build the best rod that you can and then enjoy that rod.

Take care
Roger

Craig: I certainly hope the topic is not already dead. Our attention span is not that short. At least I hope so.

Roger: I agree with most of what you say. But look at it this way. A good fly rod is the one that suit your casting stroke, and let you do what you need to do with the line. Nonetheless, it was important to describe objective properties of the rod such as action and power, if only to allow meaningful comparisons and to provide some useful info for the online buyer.
The fact that it is the fisherman that fishes -- and not the rod -- do not mean that rod properties are not important.
Here's another aspect of the problem. As a moderator on a rodbuilding forum, I feel it is my duty to provide sound answers to questions about guide choice/placement. We know that some of the answers are incorrect (eg more guides = more sensitivity), but I think there is more to the problem than we know already. The point is not to say "do this and you'll feel the bites". That's as silly as "fast rods are better". But I'd like to say to someone "under circumstances XYZ, a rod build according to such and such principles transmits better impulse and vibrations".

We all have experienced that some rods are more sensitive than others. I for one would like to know why.

_______________________________________________
If I'm not going to catch anything, then I'd rather not catch anything on flies.

Prostaff Rodhouse
[www.rodhouse.fr]



Edited 1 time(s). Last edit at 10/26/2012 03:01PM by Laurent Keiff.

Laurent,

You are barking up the right tree with your stiffness to MOI ratio. Of secondary consideration are assembly technique and material selections. It has been my experience that excessive use of epoxy (both finish and adhesive) and improperly fitted components can take away from the sensitivity/performance of a rod. For material selection, the goal would be to use materials that are mechanically similar as possible to improve the transmission coefficient at surface boundaries. Beyond that, if it is shown that certain frequencies are more important, materials and geometries could be tuned to select those frequencies and reject others. There is still a lot that can be learned in the mechanics of bite detection.

As you note, the guide train has the largest impact on the sensitivity of the rod, and everything else is less important, but when you consider the sum of the parts a few grams here and a few grams there in the handle really add up to a significant difference. When I look at a build, I consider 3 things, ergonomics, fishability, and aesthetics. Ergonomics comes first. If the rod is not comfortable to fish all day, it may as well not be in the boat. Fish fish fighting ability comes next. Does the rod have enough guides sized and spaced properly to perform the required tasks. Once these two criteria are met, I ask myself is there anything that can be removed from the rod without compromising either the ergonomics or fishability of the rod? Then finally, comes aesthetics. The goal is to start with the best fishing tool possible for the task at hand and then ask what compromises should be made for the sake of aesthetics, and where will they have the minimum impact on the ability of the rod to perform its job.

Joe

Fantastic imput, Joe. Thanks!
You, Roger and Mo made an important point, I for me at least it wasn't clearly articulated as such: sensitivity is not only about the transmission properties of the rod, but also about the way the rod affects the hand. In order to be a good transmitter of information, it needs to allow the hand to stay relaxed.
Maybe it was obvious to everyone, but at least it was not for me, so at that point the topic is already successful. thanks again.

_______________________________________________
If I'm not going to catch anything, then I'd rather not catch anything on flies.

Prostaff Rodhouse
[www.rodhouse.fr]

Rod Sensitivity.

Big topic!

First of all, there are far more important factors to the topic of rod sensitivity than has anything to do with any component of the finished rod itself. However rod balance is probably the single most important factor pertaining to the rod (assuming that one is using a modern blank made from modern materials). Its an apple to apple thing.

Other factors such as type of fishing, how the rod is loaded under the fishing conditions, LINE and its length while fishing, weight of the lure, line drag through the water and last but not least the fishermans nervouse systems ability to react to the vibration transmitted to the hand and then to the brain.

Here is an example of what I mean.

Take two rods built exactly the same, put the same reel on them and put braided line on one and mono on the other of the same weight. Now put a 3oz jig on the business end and go to 120' of water and drop to within 1' of the bottom. Start jigging one guy can feel 2" herring attacking his jig, he can feel the hook tapping the rocky bottom, he can feel the jig vibrate on the upstroke.

The other fisherman cant feel anything not even the bottom when the body of the jig hits a solid object. WHY? The line. Mono vs Braid. Not the topic of this thread but applicable, mono has 33% stretch as well as other properties that adversly affect the ability of the line to transmit vibrations and tension to the rod tip as compared to braid.

Bobber fishing has its own issue where the line has no affect because the line is slack to the bobber and that style of fishing is visual. A doug fir branch would work just as good as a 500.00 rod at least until the fish is hooked:)

Rod sensitivity has so many variables you need to realize that the blank its self is just the first thing in a long list of variables of which the majority dont have anything to do with the rod.

Sensitivity, in my opinion, is a marketing gimmick because of all the combinations of things that affect how a rod performs and the ability of modern blanks to transmit the most subtle vibrations. I recommend focusing on rod balance with reel attached, keeping the rod within the limits of the line and terminal gear, and sized to the type and style of fishing.

Joe,
You are barking up the wrong tree, actually several wrong trees. Most of what a fisherman feels will be an impulse and not a frequency or if it is a frequency it will be at the rods resonant frequency. The reason is that the mechanical impedance of the rod drops dramatically at the rods resonant frequency. All other frequencies other than the resonant frequency see a much higher impedance. If you are familiar with electrical circuits, the curve looks just like the curve of a series resonant electrical circuit and the matth is the same as well. The mechanical impedance is a function of the mass density and the elasticity. Again if you are familiar with electrical circuits, mass density and elasticity act just like capacitance and inductance act in an electricl circuit.
For a number of performance reasons in addition to sensitivity, when building a rod the rod builder wants to get as high a resonant frequency from the rod as he or she can get and this is achieved mainly by adding as little mass as possible.
To demonstrate this, deflect the tip of a rod and release it. It wil oscillate at its natural or resonant frequency. Now attempt to make the rod oscillate at any other frequency. You wiill not be able to make it oscillate at any other frequency with out putting a great deal more energy in and even then you will only get it to oscillate at twice the resonant frequency or with even more input energy four times the resonant frequency.



Edited 1 time(s). Last edit at 10/27/2012 02:43PM by Emory Harry.

Emory,

I agree about the resonant frequency being important to the efficiency and sensitivity of the rod, as it is a great way to see the effects of everything we do to the rod that affects its efficiency.

I also see where I was going wrong with some of my thoughts, and that throws out a few things that were running around in my head.

Thanks for straightening me out. It's time to put the pencil to the paper instead of thinking out loud.

Joe