Joe,

Sensitivity is a very complicated issue and at least you are thinking about it. Most people just accept the definition, stiffness divided by weight, but this is very over-simplified. One of the reasons that it is important to understand resonant frequency is that how much of the energy arriving at the tip of the rod that gets to the fisherman's hand and what the fisherman or fisherwoman senses is very time dependent. The last few years I have done a lot of looking into it and now even have a way of measuring what I define as sensitivity. An in depth discussion is too complicated and long winded to go into here but if you are interested there is a lot of good info on the Internet. It will take a little effort but if you look under "vibration, transmission of vibrations, and resonant frequency and do a little sorting through the noise you will find a lot of exellent information.

Emory, in short, build as lightly as possible with as neutral a balance around the hand grip as possible? Or do you ever have a reason to add some weight or have the center of gravity away from where the hand actually support the rod? I assume the reel weight also plays a role and should select as light a reel as possible.

Thanks,
Mo

Emory,

That's the problem, I've done a little too much thinking, and not enough work on the subject. I'll do some more reading and sit down and do some calculations.

Joe

Emory: thanks for your comments.
A couple of questions:
1. Did you publish your definition and your empirical results somewhere?
2. have you any reason to suspect that guide geometry may affect sensitivity, other than because of the implied weight?

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

Prostaff Rodhouse
[www.rodhouse.fr]

Mo,
No, I do not add any more weight than is absolutely necessary. Any added weight including weight added to achieve balance reduces the rods sensitivity.

Laurent,
An article was published in RodMaker a number of years ago but it had several errors in it.
I do not see any reason for the guide geometry to have a significant affect on sensitivity other than as you point out weight is increased.

By the way, to be technically accurate it is not really the weight but the mass that reduces sensitivity but for most purposes they can be thought of as the same.

Under what circumstances would weight and mass NOT be the same?

It seems nit picky, but the concepts of mass and weight are different. Weight is the result of the gravitational attraction between two objects, and mass is the amount of matter that is in an object. In our everyday experience, they seem similar, but a 1kg mass weighs 9.8N or 2.1lbs. on Earth, but on the moon the 1kg mass weighs 1.6N or 0.3lb. Mass, a scalar quantity (magnitude only), is a measure of an object's inertia, or an object's resistance to changes in velocity, and weight (a vector quantity, magnitude and direction) is how hard the Earth pulls on the object.

In our everyday experience we use the units of mass and weight interchangeably, but they are very different things in the grand scheme of things. The biggest problem is that we often speak in terms of kilograms (SI unit of mass) and pounds (English unit of weight). The English unit of mass is the slug, the amount of mass that accelerates to 32ft/s in one second, and weighs 32lbs on the surface of the Earth.

The answer is that they are never the same, but because we live in a pretty uniform gravitational field, the concept of mass and weight blur together, because equal masses always have the same weight.

Joe



Edited 1 time(s). Last edit at 10/28/2012 02:40PM by Joe Vanfossen.

Joe,
Excellent explanation. The reason in custom rod building that we should probably use mass rather than weight is that what really affects most rod performance including sensitivity is inertia. Inertia is an objects (fishing rod) resistance to change in velocity or change in position and inertia is the result of mass while weight does not have inertia.

After having read all this discussion I grabbed my twenty or so rod blanks in the shop and a bunch of rods say maybe eighteen to twenty and did the blindfold paper clip test on the rod tips. Anyone ever heard of this? Its a test to see if you can tell the difference blindfolded when the rod is gently tapped with a paper clip that has been straightened out. Here are the results. A big fat you cant tell any difference between built rods or blank only either strong handed or weak handed, whether its a tuna blank or a 300.00 fly blank. They all feel the same just a subtle tap tap. Its amazing that the materials used to make the blanks all pretty much do the same job as felt by the hand. So I wonder why we have spent so much time on this subject when there are much more important things that affect what I think we really want to achieve. How to make a rod feel what you think you should be feeling under real world fishing conditions. Let me know if I am missing something unless the discussion is just to discuss physics all be it a great subject.

Can anyone give me a good answer as to why all my built rods and blanks feel the same when very gently tapped whith a paper clip. So I dont get any funny answers I was completely sober when doing this test with hearing protection to eleminate the sense of sound. I was trying to achieve results with just the sense of feel. I will agree that the frequency of vibration does change from blank to blank but not at a level that the human anatomy can tell the difference.

Matthew: hopefully Emory or other more knowledgeable than I am will answer, but it strikes me that you're only testing for a single impulse and not for vibrations.
In my experience, there are very noticeable difference in the way a single blank will convey the vibrations of the caudal of several different soft plastic lures. You'll probably find even sharper contrasts from blank to blank.

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

Prostaff Rodhouse
[www.rodhouse.fr]

Emory,

The light bulb is finally on in my head. I'm embarrassed to say that I had some thoughts so far off in the woods. I started down the path and could no longer see the forrest for the trees. You can now smack me in the head again if I'm still barking up the wrong tree. It is the impulse, change in momentum, that we feel when our lure stops along its direction of motion (with decreases in tension being a much more subtle feeling than increases in tension, particularly when the lure stops). Any change in direction orthogonal to the direction of motion does not result in a change in tension of the line and thus cannot be felt, as obviously, transverse waves are very quickly damped by the water. I was too busy thinking about what happens after some of the signal gets transferred to the rod that I had ignored some of the basic physics at hand.

Thanks again for straightening me out again,

Joe



Edited 1 time(s). Last edit at 10/29/2012 06:33PM by Joe Vanfossen.