DON'T BUY CND RODS

Discussion in 'Spey Clave' started by kamishak steve, May 1, 2012.

  1. yuhina Tropical member

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    Rolf,

    I sincerely think your enthusiasm in physics is admiring, this is true words from my heart (not sarcasm).
    However, if we want to continue this physics/mechanics talk, there are a lot of basic bases you need to brush up. Otherwise, it would be just random talking with less conclusion.

    In short, gravity is a special form of acceleration. It has nothing to do with the spring motion we have discussed above. If you don't understand this... there is a great online classes from MIT (Dr. Walter Lewi), please check it out. see below. Mark

  2. TrevorH Active Member

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    Mark,

    I think you are missing Rolf's point. When a rod is circling up into key position, let's say at 45 degrees above horizontal, the rod is subject to some degree of gravitational pull that the caster will overcome on the forward stroke, even if it is slight. I'm not weighing in on whether I think it's a net positive or not, but I don't do much fishing in a zero-gravity chamber or with weightless rods, so I'd certainly consider any model of casting that ignored gravity to be incomplete.
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  3. James Mello Inventor of the "closed eye conjecture"

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    Regardless of the mass, the 9.8m/s is tiny compared to the transition from 44m/s to 0 when the rod transitions from unloaded to loaded. Gravity has some role, but it's probably more of an effect on the line as it gets sticky when sucked into the meniscus of the water.
  4. yuhina Tropical member

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    Trevor,

    No, I did not. Please view back to Rolf's post. He is talking about the "massive tip" and how it impact on "casting spring". This is not relative to the subject you just describe (D loop and gravity). In general, we have to confine the mechanic discussion in certain degree (under certain assumption) in order to clarify some specific/ particular effect. Otherwise, it will be very hard for dissecting the particular effect. (remember, Rolf brought up the gravity, not me. And he did so for the very reason - dissecting the particular effect). In reality, fly rod is also used as a lever. We should also include the lever effect in fly casting.

    The very simple experiment to test Hooke' law and constant K is to put a spring horizontally on a table. Then press the spring with force and see the spring motion in action. There is no gravity involve in this system. (to simplify the explanation for this forum) Hooke's law still followed.

    As I said earlier. I admire Rolf's spirit in discuss physics. But it would be very difficult for any progressive discussion if you can not distinguish "weight" and "mass".

    In short, when discuss momentum and rod load, we should focus on the head (line) weight and how it impact on the rod action (rod bend). Not just wiggle the rod and feel the rod tip load the rod bend. I think James also has stated it very clear earlier. Rod action should be determined and tested by line weight/ and momentum. Not just wiggle the empty rod. Overall, I think this is how far we can go, no need to discuss the combination effects when combine lever and spring.

    Cheers,

    Mark
  5. TrevorH Active Member

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    James- I would agree that gravity doesn't play nearly the role as that played by the rod's own inertia and inertia of the line in providing resistance for us to bend the rod butt against, but I believe that consideration of any facet or combination of facets is best done within the context of as complete a picture of a cast as possible, so I won't dismiss the role of gravity, it'll always be part of the picture.
  6. Klickrolf Active Member

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    Klickitat, Washington
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    Initially I questioned the wisdom of lighter rods and lighter rod tip sections. Rob, Trevor, and a few others agreed because they know what we were talking about...they have experienced it. My inclination to push it came because I don't care about an extra ounce in a rod if I like the way it casts, but I do care about breaking a rod. So, I like beef in my rod tip section. There's too little beef in the CND custom rods.

    Mark, you've not really tried to understand my posts have you? You've assumed I'm an idiot from the start...your condescension is overflowing. If you looked at the link I provided "twice" you'd have known I'm aware of the difference between mass and weight. You didn't care about that, you just knew I was an idiot!! But, on planet earth mass and weight are correlated. Therefore one can use either term interchangeably...as long as we're talking (or fishing) on planet earth.

    Gravity is the casters friend when loading his rod but his enemy once the line is released!

    Good spey rods don't have wimpy tips.
    Sometimes the obvious is overlooked in a search for complexity!
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  7. TrevorH Active Member

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    Mark-

    I can really only remember making essentially 2 points in this thread, one of which I just made again in the above post, that of firmly believing that the most productive modelings of casting will always account for MORE variables/facets, not less, as you suggest is necessary in order to clarify some specific/particular effect. I went as far as to mention that over simplifying the model can actually skew your perspective on what is taking place, which I've both experienced and seen take place. Regarding rod action, it actually blows my mind a little bit that you seem to be disregarding the effect of the rod's own inertia on it's action. I have more than a dozen spey rods and I've cast every single one of them against the others with the express purpose of ascertaining the degree to which the rod loads under it's inertia vs. the inertia of the line, and there is unquestionably differences in how they load. If your only point has been that the rods least affected to load by their own inertia are theoretically the most efficient spring/levers, I've never argued that, but that doesn't necessarily make them the "best" rods. I'm not disputing the physics, just the application of it. I also never argued that the design philosophy of producing low inertia rods hasn't produced some great rods, I have a few that I love, but I cannot fathom a world of rods that don't load to some degree under their own mass. What a sad place that would be.
  8. yuhina Tropical member

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    Trevor,

    I totally agree. We should take the whole real situations into account regarding casting mechanics. Oversimplify situation is just a steppingstone for us to understand some particular force or effect. However, it seems we never get over those steppingstone explanations because (some of us) the weak understanding of some basic physics. No offense. For example 1, do you see any "gravity" component in Hooke's law? No, because gravity "can" act as a "force" component (on a given mass) on a spring, but Hooke's law is all about "force" and constant K. You don't need "gravity" but you need "force". This is reason I said " gravity is a special form of acceleration", but not all acceleration acting like "gravity". This go back to "salmon and fish" analogy that I mentioned earlier to Steve in this thread.


    Do I blow you away by not mentioning inertia? really? Could you write down the formula of inertia?
    If I remember it right, I have mentioned the term "momentum" for many years. Includes the rare form of momentums - the angular momentum and how it relate to circular casting motion. I also mentioned the momentum in my first post in this thread. Anyway, this is just give you an idea of what I mean by lack of bases. Really, I agree with you, it's good to model everything into the casting mechanics. It just the matter of "when" we will get through those steppingstone explanations. Now imagine put the blank thickness and air resistance into the casting motion. Understanding the reasons SAGE ONE is trying to pack more fibers into the rod blank, increase rod power and make a thin blank. Thin thick wall blank (thin diameter) helps the rod to cut through the wind, but it also reduce the "good" rod bend created by air resistance (sounds weird?). (rod bend created by air resistance is bad, just to be sarcacium ). But, this is the same false logic when we talk about how good the massive rod tip "helped" the casting energy. BTW, I am glad to see more people are starting to use "action" and "power" to describe the rod characters. Watch the movie more closely and we will understand using lightweight; more powerful material is not a redundant move at all. (Disclaimer: SAGE did not pay me for making those posts... but I think they should! )



    Rolf, No, I don't think you are an idiot. I was just not sure if you misunderstanding the concept of "g" and "force". My apology to sound like condescension. As I said earlier, good for us to learn more in casting mechanics and recognize the different effects... it will take a while for us to get to the final complex model. Now it is very good and interesting you have introduced the trajectory motion on fly casting, the "g" should be included in this casting motion.

    I also wonder if you understand gravity/ acceleration is a "directional" vector. During a fly casting motion, accelerating a back cast (parallel to the casting ground) will facilitate the rod load in following forward delivery which is perfect alignment (0 degree, or 180 degree). However, gravity is always pull perpendicular (90 degree) to the casting stroke, which means do not acting upon the horizontal casting stroke.

    Good luck on the discussion!

    Cheers,

    Mark
  9. TrevorH Active Member

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    Mark-

    No rod bend that ultimately unloads to propel the line is bad, unless the cost is too high to get it. Air resistance, as it is friction, is bad, but has no relation to inertia, which is resistance to change in motion. I'm off to work, so I can't reply much further, except to simply say that the most efficient spring doesn't necessarily make the very best rod, which I think I've said 6-8x in a variety of ways. I believe you are letting the physics lead your thinking a bit. At least in this instance, I mostly agree with your physics.

    Edit: Rereading your post, I'm forced to wonder aloud just what your physics background is. I had a year of physics in college, as I'm sure many on this site did. No offense, but while you seem to have a solid grasp of the concepts, your application to the real world is shakey at best. Is it a spring and a string, or a trebuchet and a steel ball? There's a hell of a difference.
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  10. TrevorH Active Member

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    Well, I'm getting rained out of work, so I'm going to take one more run at this, and I'll actually take the time to type out a picture of what I see, which differs somewhat from a spring on a table. That said, I'm still going to try to keep this short.

    When I am moving from my sweep into my circle up, I frequently make the effort to drift back into the d-loop by rocking onto my back foot, rotating my trunk a bit, raising my arms, etc... As my d-loop fully forms, I reverse this sequence into my forward stroke before I ever start the push/pull work on the rod with my hands. In doing this, I shift the base of the rod without really initiating the casting arc and pre-load the butt of the rod. Rods that load to some small degree by virtue of their own inertia take this pre-load more easily than ultra-low inertia rods do, but I do it with all rods. I then move into my forward stroke, stop the rod, and let that pre-load propagate out through the tip. Now, I never said that ultra-low inertia rods don't make the best springs, but I want some degree of inertial loading in most of my rods as I can consistently unlock the power of the rods butt section, and all things considered, I think they make for better feeling rods that move plenty of line. The truth of the matter is, ALL rods exhibit some degree of inertial loading, as NONE of them are mass-less, it's simply a function of how abruptly you want to apply force. I get an inertial load on my T&T rods when I want it, but I have to be firm with them about the matter.

    Anyways, I'll go a step further and say that I suspect that mass may have something to do with why some of my rods are able to unstick heavy loads in certain conditions better than my light-tipped rods which seem to offer precious little input as they approach and go past straight on the unload, but that is actually inserting real fishing conditions into the assessment, which complicates things. Like I said early on, I think it's a matter of balancing feel and load-ability with firmness, recovery speed and swing weight. The equations would have us believe that all rod mass/inertia is bad. I say that in the real world, it always exists in relation to supporting stiffness, and where appropriately allowed to exist in a world obsessed with swing weight, it can and does have a positive role in rod action and performance. That said, I love ultra-low inertia rods too...

    I feel like I've said all of this in one form or another already, and frankly, I'd be happy to find out that this is all my imagination and I'm totally full of sh*t, cause I'm always looking to step my game up, but I want to hear it from an F1 caster and/or an F1 rod builder. Mark, that honestly isn't meant to be a swipe at you. I'm not questioning your handle on physics, just the readiness with which you espouse conclusions based on simple models. It is fully possible that I'm just a blathering idiot, and I'm prepared to find out that's the case, quite comfortable, in fact, which may be part of being a blathering idiot. I don't really know...
  11. James Mello Inventor of the "closed eye conjecture"

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    Err, not to be a dick, but if you only had one year of physics, then you're probably not qualified to say someones physics is :shakey at best". I was a physics major at UW before the dot com explosion sucked me up (3rd year, quantum + general relativity), so while I'm not an authority, I do have quite a bit of experience in this matter:

    As for the arguments and why there are issues with them, the hole gravity influence is a perfect case:

    9.8^2 == 96.4

    44^2 == 1936

    This is 4% of the total force involved. Relatively tiny compared to just the momentum of the line. Also since momentum is M*V, if you are only accounting for the momentum generated by the line in regards to gravity, then you are only looking at a smaller mass being used (even at the vertical) in the total weight versus the whole line moving horizontally away. That's why most rods, even with beefy skagit heads aren't loaded by the line for the most part, even at horizontal....
  12. James Mello Inventor of the "closed eye conjecture"

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    I need to call myself out as there was a poor explanation on the above. The value of 9.8 ^ 2 is incorrect as it is actually the *velocity* of the object that determines the value of the kinetic energy. In this cast, let's assume the loading of the rod takes 1 second, then this above would be correct. Seeing that it usually isn't one second for this, the effect of gravity pulling down will actually be substantially less.
  13. KerryS Ignored Member

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    Wow, all of this because some guy doesn't like CND rods. Again I think I will go fishing and this time I will use a Sage. Hoping there isn't as much physics involved with the Sage rod. If I had to know all of this shit to cast a 2 handed fly rod I would have stuck to using a stick, some string and a safety pin.
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  14. James Mello Inventor of the "closed eye conjecture"

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    Actually he likes the rod Kerry, just not the service :) Jeez, you'd think you'd remember this from 7 pages ago!
  15. TrevorH Active Member

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    James- I'm happy to concede that I'm no physics expert, but I've never pretended to be one, either, and I'm not sure an expert is actually needed to question some of what has been floated on this forum. As far as the gravity thing goes, you'll see in my first mention of it that I knew it's affect was slight, and didn't weigh in on whether it had any real impact on loading.
  16. James Mello Inventor of the "closed eye conjecture"

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    I ended up lumping your statements with Mr Rolf's... Sorry about that!
  17. TrevorH Active Member

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    James- I'd like to hear your thoughts on what I've actually said...
  18. speyghillie speyghillie

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    River Spey Scotland
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    Hi All,
    It seem this thread is still going strong, and i wondered after all the debate can a fishing rod be a true lever if it is not spliced, i refer to my post with the picture much earlier,
    Cheers Gordon,
  19. inland Active Member

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    Complex tapered spring/lever moving a tapered weighted String. Whether or not gravity does much to the rod itself while working, it sure as hell creates everything that is river spey casting. Starting first and foremost with running water. Between all else the rod does not bend or cast on its own. The line does not jump out of the water and magically drift off into space. Nor does it move forever. Gravity eventually always wins. Gravity also makes grown men of today whine and cry because rod Y weighs an extra ounce point 5. Oh dear I think my arm just ended up being longer than my other one. There isn't one of us on this forum that can extract everything out of the spring levers being made, why get all twisted up on ridiculous marketing hype to make them even 'better'? Certainly a good thing to improve fiber count and resin properties. No doubt. But to claim it does this and that and this and that, so does a rod from 150 years ago...if you are capable. One may be easier. Weigh less. And 1000 times more overall performance potential. But no matter how great that difference, the person doing the casting is always going to be the weak link. I am amazed every time I take 7 steps back and cast the wood rods of old. No they don't cast for shit if you treat them like a modern graphite tube. Spend some time and figure out how to cast them and then comment back on how far we think we have come. The stuff made today, even in the past 25 years is so fucking silly easy in comparison. Still a complex tapered spring/lever moving a tapered weighted string.
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  20. Big Tuna Member

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    I'm with Kerry. Glad I was one of those soft science English major morons.