thanks for your explanation, Gordy.
i am fully aware of the force over distance principle but i wasn't addressing that.
if a student asked me "so, what is a properly loaded rod ?" that is the short response i would give. an important part of teaching is to help the pupil find solutions on their own while being guided in the right direction. nothing's better than watching their expression when all of a sudden they put the pieces of the puzzle together on their own.
That is a useful endeavor and should give more information about how a rod might perform over a range of casting distances, but I think most good casters will still determine a preferred rod/line combination by test casting, not by looking at measured data.
if a student asked me "so, what is a properly loaded rod ?" that is the short response i would give.
Marc,
I would be interested to know how many instructors have had a student ask such a question. In my experience they are very interested in learning what to do, but have zero interest in why.
As you probably know I have an aversion to the concept of "loading the rod" as I think most people think that it relates to loading the rod with potential energy that is then converted to K.E. in line as it "unloads." That "big spring" concept is a widely held idea about the basic physics of casting (even from Master instructors ), but I am surprised it is still being asked in a casting instructor exam.
If a student asked me what is a properly loaded rod, I would ask him what that term means to him and what does he thinks he is loading it with. If they have been exposed to traditional casting literature they will most likely respond they are "loading" it with potential energy to produce line speed.
If that was the case then I would say that is not the purpose of bending the rod and explain that when the rod is bent it will apply an acceleration force on the line. As he rotates the rod that force will accelerate the line over the distance the tip moves. Putting more bend will increase the acceleration force and/or applying that force over a longer tip path will produce more line speed.
If his eyes roll up in his head as he really wasn't interested in the why of casting (I have only had one student who was interested in the underlying physics of what he was trying to do), then I would tell him to just accelerate the rotation of the rod to a firm stop and not worry about rod loading, just get it to bend more over a longer tip path.
If he understands what acceleration is and can learn to make a firm stop, then he will start to make loops.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
From this experience, I conclude that ERN is not enough to recommend a line number, but that AA can compensate this “weakness” since it has a meaning in terms of line fit through the effect of non linearity (and not only in terms of “action”, or “speed”). But that it can be improved, thanks to understanding rod behavior through modeling.
Thanks for the confirmation.
I have to start back in this and work though it but does the expression 'Hammer to crack a walnut' translate?
In my experience they are very interested in learning what to do, but have zero interest in why.
Easy to agree with that Gordy, I watched half a dozen demo's at a show yesterday and they all centered on 'why'.
Btw I heard one explanation which maybe used a 'big spring' argument. More interesting I watched a couple of sessions about French Nymphing, casting and fishing without flylines may leave a lot of this type of debate looking redundant.
My apologies for taking time coming back to you but I have been away fishing. I will not go over ground that Merlin has already covered but I will try and give you my experiences so that you can understand why I have looked at this so critically.
"While ERN does give a view of stiffness it has limited utilit". Yes indeed. But is it helpful for me to understand how stiff the rod is independent of length?
For me it is. During summer I fish small streams with rods I have built myself. Most of my rods are under 7'6" and about #3. In winter, I fish for grayling on the larger chalk streams and for that I have rods of about 10' #3. During these builds, I found variances in their ERN. So for me, consistency across ERN is important and that is why I would prefer the use of standard units.
"Similarly, using a 1/3 of the rod length to gain a deflection to take the ERN/AA measurement assumes that the angler is only interested in the top third of the rod. ". Sorry to say, but you are incorrect. You have to remember that at any load all the rod is bending, not only the top third.
I think we are agreeing about this point and I am interested in the bend form tip to butt, especially if I am building on s-glass for the small streams. i would like to know if the rod will fold on me at any point.
Rods do NOT have ERN higher or lower than line weight. Rods have an ERN. Its up to us to decide how stiff rods we want, and to choose line weight based on knowing the rod (stiffness and action).
I have taken the CCS direction literally, such as this from the CCS article:
An average rod designed for a No. 6 fly line should exhibit an ERN value of 6.5. The force required to load a rod defines its weight designation. If the ERN of a rod is less than 6.00 or greater than 6.99, it cannot be called a 6-weight rod.
I am guessing that you are using the experience you have gained over time to make judgements based upon the CCS measurements.
When I talked about this subject in the Tackle thread, I referenced a Parkinsons paper on tapered rods. In his conclusion he makes a connection between the ratio of the MoI of the endpoints of the rod and the elliptical tip path. Are you seeing the same relationship between your measurements, AA and the MoI?
As an additional thought before I go; is there a relationship between Parkinsons findings and the Grunde/Magnus swingweight technique?
I shall give a look at this point (MOI vs AA). Not sure the relationship will be as good, but who knows before trying?
Can't tell about MOI measurement technique from the SL publication, but it is based upon simple mechanic concept, with an assumption about linear density, as far as I remember.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
Replace the nut by a fly and you have got it. Your casting skills and rod test experience allows you to consider those things quite straightforward but most of us can't (any consulting for a british rodmaker?).
It would be nice if you could advise us about the considerations to have for line fit whether AA is on the high or on the low side. It would likely be better than seeing technical graphics.
Many thanks in advance.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
Thanks Merlin, I am a bit tired from the weekend (friends 50th birthday mixed up with some wild fishing) but I get the feel that there is a relationship between your new model, AA and Parkinsons MoI. Perhaps to remove Magnus sledgehammer we could find a relationship between the tip and butt diameters.
I'll probably have a good nights sleep and find that this was all a dream :laugh:
Now that my eyes have stopped bleeding, I have read your Post #59 and found that it all makes perfect sense to me.
I have seen the line/m0 relationship during builds but change tip tops around instead of the line if I am building for small streams, where I am more interested in good presentation at short ranges rather than absolute speed. I tend to decide on size of flies to be used, then pick a line to deliver that fly and then fettle the rod to suit the line. If I give that combination to a good caster, they tend to prefer a line lighter than my design.
From this experience, I conclude that ERN is not enough to recommend a line number, but that AA can compensate this “weakness” since it has a meaning in terms of line fit through the effect of non linearity (and not only in terms of “action”, or “speed”). But that it can be improved, thanks to understanding rod behavior through modeling.
Not sure Bill is ready to buy in…
Merlin
Merlin,
Although I have no interest in linearity, I will certainly buy into what you are pushing here because I recognize you and I share a common view on frequency.
But, don’t get too far overboard with ERN and AA and recommended line number. The “correct” line number is the one which matches the frequency of the angler’s PPF. You can’t model that.
In your NF vs AA chart, I might consider, not a strait line, but two curves, one below 70 and >70, and how the change might be effected by the nonlinearity of ERN.
Bill Hanneman wrote:But, don’t get too far overboard with ERN and AA and recommended line number. The “correct” line number is the one which matches the frequency of the angler’s PPF. You can’t model that.
I don't get this "matching the casters PPF" idea...
My experience is that for a given line length (and weight) the caster uses almost the same stroke regardless of the action of the rod. Different rods certainly "feel different" but there is little or no "adjustment to or matching of PPF" going on.
Let's face it, we need to be able to cast anywhere from our feet to the horizon, ...
Which I agree wholeheartedly too. Forcing this way of looking at fly rod and caster performance into a "matching your PPF" picture is at best confusing; when it's all about matching power application to the line length and weight (+ fly rig) you are casting.
Cheers,
Grunde
"Essentially, all models are wrong, but some are useful."
George E. P. Box
Thing is, the way I read "The “correct” line number is the one which matches the frequency of the angler’s PPF" it says something like 'ultimately the 'correct' line for a rod is the one the angler likes using.' Which I think is mostly true I read that as a statement that there is a subjective element in rating a rod.
The “correct” line number is the one which matches the frequency of the angler’s PPF. You can’t model that.
Bill,
Can you measure PPF or is it just a "meager kind" concept.
Do casters have just have one fixed PPF regardless of how far they are casting?
I would think that most good casters change their tempo as they cast from their feet to the horizon.
Lasse showed that it is not necessary, but I would also think your tempo would be slower using a bamboo rod than it would be using a fast graphite rod when casting 50 feet of line.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
Correct me if I am wrong but I think UC Davis University acknowledged that casters correct their style unconsciously.
And of course counsciously for the example you speak about (slow cane / fast graphite).
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
I read that as a statement that there is a subjective element in rating a rod.