Can any one explain to me what comprises a semi-parabolic action or taper? Again, just curious.
Thanks.
Bob
Thanks.
Bob
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Semi-Parabolic??
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 bobbeegee |
Semi-Parabolic?? |
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Posts: 1802 07/13/2008 18:06 |
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fishbum |
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Posts: 159 07/13/2008 19:57 |
Garrison spoke of his rods as being semi-parabolic. I would guess that any rod whose stress curves resemble a Garrison would be called semi-parabolic.
fishbum |
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Marshall8 |
pull this up | #2 | ||
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Posts: 737 07/13/2008 23:37 |
Bob,
See if this pulls up: http://www.uwm.edu/~stetzer/Tapers/hexrod-archive.html#dickerson Look at the Dickerson 8013 stress chart to see a progressive action Check out the Garrison tapers and many others for semi-parabolic. They kind of go straight across the page with some tapers having some blips up and down. The Pezon tapers are generally parabolic although the first example on this site is purely a progressive action. The more you look at this stuff especially the ones you have cast the better idea you will get what a rod might feel like in hand if you have its taper. Hope this helped, Marshall |
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bobbeegee |
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Posts: 1804 07/15/2008 07:20 |
Thank you Marshall. Very interesting.
Bob |
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J W Foster |
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Posts: 8 07/15/2008 09:37 |
Hi Bob
Before you get excited about semi-parabolic remember that it is the biggest red herring of all the naming conventions. A rod is either straight or it's not. It's either parabolic, or it's not, although para rods are not parabolic. It's just a name, not a real mathematic function when it comes to rod design. Garrison rods are known for their flat stress curves, flat stress is not semi-parabolic.. In fact, a flat stress curve yields an constant rate of deflection for every inch along the rod, which is a perfect Arc. And as Tom Fulk has shown, a Perfect Arc stress curve yields a perfect para rod (in name only). Can anyone describe the action of a semi-para rod, I don't think so. I'm currently designing a rod which could be best described as a decaying sinusoidal shape stress. I wonder what some marketeer could do with that. Regards Jerry
Last Edited By: J W Foster 07/15/2008 13:23.
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Marshall8 |
hows it going | #5 | ||
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Posts: 739 07/15/2008 14:55 |
Jerry,
You make some great points and I really appreciate the conversations we have had that opened up my understanding of the limitations of stress charts as they apply to rod actions. What we do need is a means of communication with each other that will generally describe what we have in hand to either sell or ask questions about. Looking at a stress chart that has a line going (after the tip breaks) from high to low I call it a Progressive taper (tip action) or from low to high (heavier tip/stiff mid going softer toward the butt) it is described as a Parabolic action and a blend of both or going flat its Semi-Parabolic. The three I am using are by no means original thought and were taken from reading others comments about rod actions. Its possible that there should be more or less descriptive categories to discuss this stuff. If the current three we are using do not get it and are misslabled at best, what would you suggest we go to from here to communicate with each other? Marshall |
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aparramoure |
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Posts: 1410 07/15/2008 17:23 |
Tip flex, mid flex, flex down into the grip~
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bobbeegee |
Parabola | #7 | ||
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Posts: 1814 07/17/2008 19:57 |
Certainly not being a mathematician, or even a basic math whiz, I'm still trying to comprehend a parabolic or semi-parabolic rod.
Looking here............. http://en.wikipedia.org/wiki/Parabola I don't believe I want a parabolic taper rod! I understand these terms are more than loosely applied and are generalizations of particular stress curves. I think I can understand the semi-parabolic affirmation, as it would seem to be a rod that flexes mid to tip only? I guess a parabolic rod would flex full length, even into the butt? I'm just again, Manny, being Manny! Bob |
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hauloholic2 |
Definitions | #8 | ||
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Posts: 31 07/17/2008 23:50 |
Progressive ---- Semi-Parabolic --------Parabolic is a continuum of rod flex characters. It does not attempt to define the rod in terms of "action"
the way that today's casters use the words slow/moderate/fast. We can have slow/moderate/fast progressive rods, slow/moderate/fast semi-parabolic rods,
and slow/moderate/fast parabolic rods.
To me, the only rods that can be clearly defined are those on the very ends of the spectrum. Purely progressive rods are those rods that bend at the tip only with a light load, and then a bit more down with a bit more load, and so forth all the way down the rod. There are no surprises in where the rod bends as increasing load is applied. On the other extreme, the parabolics load the tip only with a small or moderate amount of load, and as you increase the amount of loading, the rod doesn't really continue to flex down the rod until you reach a "threshold" load -- after which the flex point jumps down to somewhere in the bottom 1/3 of the rod. When the load is removed, the rod returns to straight in the reverse sequence. With an acutely parabolic rod, the caster can discern this "jump" on both the load and unload phases of his casting cycle. Some love it, some tolerate, and some hate it. If the rod is somewhere between progressive and parabolic, then it can be described as semi-parabolic. There is no denying, parabolic rods can really toss some line once you figure out how to apply the power. For most trout fishing, the predictable nature of progressive or progressive-semi is pleasant and relaxing to many people. To me, static stress curves can somewhat predict how a rod will feel in motion, but until I cast it, I can't KNOW. And I like to know... 
Troy |
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hauloholic2 |
Oops | #9 | ||
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Posts: 32 07/17/2008 23:55 |
One more clarification --
Just because a rod bends into the grip does NOT immediately imply that it is a parabolic. It's very possible that it's just a softer progressive or semi. haul |
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magguscdc |
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Posts: 7 07/18/2008 04:34 |
Hi,
I have studied the stress curves of different taper designs with great interest (cf. http://www.uwm.edu/~stetzer/Tapers/hexrod-archive.html#dickerson) and I try to understand them to be in a position to "roughly" predict how the taper might feel ... Is it correct that a rod which reaches the maximum stress close to the tip is considered as a tip action rod and a rod which reaches the maximum stress at the middle section would be a medium action rod? I think so.... But I wonder why in some stress curves the stress declines from tip to the grip? I think that any rod becomes thicker from tip to grip.... Thus, I don´t understand why the stress may decline at all... I think that stress should increase if the diameter increases and there should be a correlation ... I have no idea how the stress curves are exactly measured... Do they apply a spring balance at different sites on the rod and measure the deflection and stress and plot the "single" values and draw a line throught the isloated measured values? Thanks for any elucidating comments! :-) the confused Markus |
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J W Foster |
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Posts: 9 07/22/2008 16:46 |
Hi Markus
And Hi Marshall, It is certainly always a pleasure to chat with you.. First I needed to re-edit my previous post.. Garrison rods are known for their flat stress curves, flat stress is not semi-parabolic.. In fact, a flat stress curve yields an constant rate of deflection for every inch along the rod, which is a perfect Arc. And as Tom Fulk has shown, a Perfect Arc stress curve yields a perfect para rod (in name only). To read, and mean Garrison rods are known for their flat stress curves, flat stress is not semi-parabolic.. In fact, a flat stress curve yields an constant rate of deflection for every inch along the rod, it is a straight line as a stress curve and almost a perfect arc as a rod deflecting.. And as Tom Fulk has shown, a Perfect Arc stress curve yields a perfect para rod (in name only). Now as to Stress Charts... There is something (but little) to be gained by reviewing them at first. For a given weight of rods you can kind of see how high the tip deflection is and where the turnover point is, and kind of where the butt stresses all end up. At some point a stress chart is counter intuitive..The chart can also be looked at as stress shedding chart. Where the tip appears to have a great amount of stress, that stress, because of the small diameter of the cane is actually being shed down the rod. We all know that when you begin a cast the tip simply gets out of the way. The high stress is because this is a static model, in a dynamic model the stress curves appear very differently. But I digress, so the stress can be viewed as traveling down the rod and each incremental part of the rod is absorbing what it can and passing the rest along. Huh? The thicker part of the rod can absorb more power without stressing, or bending as much. The stress chart is actually a close approximation of a deflection graph. 200,000 inoz2 on most graphs is about 1 deg of deflection. If you start at the butt and incrementally accumulate those points ( by the inch is fine) you get a reasonably accurate depiction of how the rod is bending. In the beginning you must cast a rod, any rod, (that has a public domain taper) and find the sweet spot for your style of casting. Then measure amount of line out and enter that value in Franks, or anyones stress program. Now you will see a picture of what you thought was sweet. There are 3 or 4 things that are important. Or maybe 20, but lets start with a few. 1. The tip stress value. Because this is the max stress point on most curves it can give you a fair picture of how you like the tip to act and kind of the general power when you (each of us) apply it makes the rod work best. the general range is from 180-240 but it will vary with each. 2. The tip stress value can also indicate how the tip rebounds 3. The tip turnover point in inches back from the tip will give an indication of loop size. I could say something general like " the farther back the turnover the wider the loop" but great casters sometimes fool me because they can control a longer tip better and get tighter loops. 4. The higher the mid point of a rod the slower it will be. 5. Butts are the most difficult because they are more important in fighting fish than in just casting alone. But in general any number below 130k is very very stiff. The shape of the curve (ignoring any blips) is generally the character of the rod. However you describe rod, fast, slow, progressive, etc. that's up to you. But the more vertical the line the quicker the rod is through that section. Actually it is slower through that section because it is bending more, but in a shorter distance. And the stress through the rest of the rod is lower (stiffer) in order to make it change rapidly at that point. The reason I put this here is to give everyone a way to individually analyze rods. Each casting style is different therefore you must analyze a rod based on your individual technique. There is no FET that everyone likes. So when you answer the question " What 7' 5wt. should I buy" you are displaying your favorite not someone else's. Or maybe just pimping a rod. If you have done all of the above with several rods, you will build a picture profile of rods you like and the characteristics of those rods. This should help you be better informed when purchase or make a rod. I am certainly open to discussion and flack. Regards Jerry
Last Edited By: J W Foster 07/22/2008 20:33.
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J W Foster |
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Posts: 10 07/23/2008 10:06 |
Hi Markus
I guess I didn't answer the other part of your question. Stress, as derived by Mr. Garrison, is based on beam theory. Basically it's the summation of the moments of inertia (MOI) of all the cross sectional areas of a rod, plus the weight of the line beyond the tip, plus the weight of the guides, varnish, and ferrules, times 4 G's (gravity) of acceleration and a tip compensation factor. He had to use a slide rule in his time so some of the more modern methods using computers are yielding more accurate and dynamic results which include Modulus of Elasticity (MOE). But his methods set a baseline and are valid in in there own sense. It is just a constant that allows us to view rods a different way. As to a Para By construction a para ( the Para 14- Paul Young is the best example) will flex in the tip has a stiff mid, and flexes in the butt. This gives it the sling shot effect that people like-or don't. The stiff mid soft butt is what distinguishes them from other rods. Regards Jerry
Last Edited By: J W Foster 07/23/2008 10:11.
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magguscdc |
#13 | |||
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Posts: 9 07/23/2008 10:13 |
Hi Jerry,
thanks a lot for your detailed explanations! :-) When reading it I learned a lot but I would say I am still confused, but on a higher level! :-) Best regards Markus |
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J W Foster |
#14 | |||
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Posts: 12 07/23/2008 12:26 |
Ok.. So join the crowd.
So to take it to a different plane.. This stuff is all about the feel of bamboo... Many people can help describe feel better than I..So jump in here... Essentially, if a rod is balanced, you will derive the feel of the rod from the middle 2/3 thirds. This is were the rod deflects the most and where the tactile feedback of the rods foreshortening take place. The tip may be bend more, but the amount of cane there is small so you get little feedback. Foreshortening is the rod getting shorter, relative to the ground as you cast, because it deflects, bends. Cane, unlike tuperware, has mass, so that mass deflecting against the weight of the lines resistance is what you are feeling, thats where the elasticity and the inertia are technically involved. The length of the rod and the various flex and set points along the rod give each one a unique feel a 7' rod that has a flex point at 20" will not feel the same as a 8' rod with the same flex point. You may prefer one over the other, thats why I talk about individual feel. A set point, as I use the term, may appear as one of the blips on a stress graph, if it was intended. This is kind of like " the darkest hour is just before dawn" thing. A rod may have a rise, or depression just before it has rate of change of dimension, just to emphasize it, or set it up. It's the same as you must actually use the most strength in casting at the change of direction to keep your wrist from collapsing. So a stress chart should be giving you a picture of how the rod might feel. But you have to establish a baseline or they are meaningless. There may be many disagreements with this assessment but...this is another part, for what it's worth. Regards Jerry
Last Edited By: J W Foster 07/23/2008 12:33.
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magguscdc |
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Posts: 10 07/24/2008 03:45 |
Hi Jerry,
thank you for your further explanations... I find this topic very interesting, because I would be glad to predict as to whether a particular kind of taper fits to my need/preference or not... So far I only know the Garrison taper 202E in a length of 7´ (#5) and I like this taper very much... When looking at the stress curve I realize that it has an almost horizonat line.... which seems to be unusual when looking at others which have peaks, a clear maximum or even a curve etc... Do you know how the test curves are exactly measured? Which tool is used therefore? Best regards Markus |
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timmy |
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Posts: 111 07/24/2008 07:25 |
Markus,
Stress curves are generated mathematically from the taper dimensions, there's no need to actually build the rod. Using a program like Hexrod or RodDNA you can enter the taper and the program will spit out the stress curve. Of course that when the fun starts, trying to figure out what the curve means. To my shame I have very little idea what the formula is, but it take account of more than just the line. The masses of ferrules and other hardware are also included in the calculations, and there are variables for the density of the cane and other things. The only one of these I tend to play with is the ferrules, the rest I leave as a constant, to help me compare curves. It should be remembered that it is an imperfect system, and two rod with identical curves can cast differently. For example, if you used HexRod to convert your 202E into a three piece, the new curve would be an exact match, but the actual rod would likely be a little slower. I think experience of a Garrison taper is a very good place to start understanding the curves, He developed the maths and so the tapers have a very consistent look (and feel) and the flat curves give a nice base line to compare stresses. for example compare your rod with a Payne 100, this rod is in some ways similar, but much more delicate due to the softer tip and higher stresses in the butt section. The 202E is probably more versatile, but the 100 is a lovely dry-fly rod. Another thing you might try is casting your rod with different line weights and using hexrod to plot curves with those lines, I've not actually tried this, but it should give you some points to compare. Or try playing with "Length of line cast" this will show the importance of comparing like with like. Ultimately though, the only way to learn is to cast lots of rods (hard work Huh?) but even this is not without difficulties. Most rod makes can't leave taper numbers alone, and so comparing them back to published tapers might be difficult, even if they did use the numbers without fiddling, which set? and that's before you get into all the variables that rod makers like to argue about. Glue, heat treatment etc. etc. Tim. |
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magguscdc |
#17 | |||
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Posts: 11 07/24/2008 08:29 |
Hi Tim,
thank you for your explanations! Now I understand that the stress curves are not actually a measured curve but stems from a mathematic calculation.... I was rather astonished to find a huge number of taper stress curves.... I could not imagine that all of them were measured in a complicated way ... :-) I see, I have to throw and throw and test and test.... Unfortunately it is not that easy to find a lot of rods to compare... Anyway, I will try it... best regards Markus |
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