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Location: Eagan, MN | Here's a mind-bender for all you engineering-minded folks out there, of which I am not one.
So, I'm wondering about the physics of rod length decisions. My questions are this:
1) In engineering terms, is a fishing rod more akin to a lever? Or a spring? Or a combination of both? How does a change in length effect load lifting ability or what some guys call 'power'?
2) If a rod is more like a spring, then what happens to the potential to store energy when the rod is flexed as a rod is lengthened or shortened?
My very basic understanding is this: if akin to a lever, as a rod is lengthened, the angler loses power, though gains the advantage of rod tip speed. If a rod is also akin to a spring, there is a greater ability to store more energy as length is increased, thus in theory improving fish fighting ability. Curious how the two concepts might interact though since a rod is neither exactly like a rigid lever nor a spring, but seemingly a hybrid of both.
I'm just wondering about the physics, both positive and negative, of changing rod length from what was once 6', to now 9', and possibly 12' in the future. Each step up in length has changed how I've had to think about fishing...and how I've fished.
Am I thinking correctly about the physics of rod length decisions? Who wants to tackle the questions posed above and put them in terms that layman like me can understand?
Brian |
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| I think your basic understanding is correct; it's a lever and a spring; a cantilevered rod capable of large deformation. How far do you want to go? http://iweb.tms.org/ED/01-5085-161.pdf Have fun!  |
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| BrianF. - 4/17/2015 5:33 AM
Who wants to tackle the questions posed above and put them in terms that layman like me can understand?
Brian
I think you just did it. Here's a little more, if you want.
First to discuss the concept of the rod being a lever:
It is just like you’ve said, if I understand what you mean by “the angler loses power” as the rod is lengthened. Most people understand the concept of a lever, but I’ll summarize anyway. When you’re holding the rod horizontally (straight away from your body) in your two hands with a bait hanging down, your two hands are providing what’s called a “couple” to counteract the “moment” caused by the bait hanging at some distance away from you, out on the end of the “lever arm” (rod). Lengthen the lever arm, and the moment increases, so you have to increase the couple to counteract the moment.
Now, when it comes to sensitivity, that long lever arm works to your advantage. A longer rod will magnify the “feeling” of bites, when blades stop spinning, etc. (all changes of line tension) when compared to a shorter rod (as long as your rod isn’t pointed straight at the bait, because then, of course, there is no lever arm).
Now rod stiffness. This isn’t as straight-forward as the lever-arm discussion, because many things come into play. The rod’s material and geometry determine not only how much it will flex, but where the flexure occurs along the shaft, how quickly it will return to its unloaded shape (straight) when a load is removed, and how much it will undulate before becoming perfectly still again. For a mental picture, think how rods like Berkley’s Ugly Stik are known to “wiggle” a lot after you make it suddenly deflect (bend).
In theory, no matter the stiffness, the stored energy in the rod is the same. It’s called “strain energy”, strain just means deflection relative to its original shape. Strain energy is inversely proportional to the material’s stiffness (actually, modulus of elasticity, but “stiffness” will do). So if material A is twice as stiff as material B, it will deflect (bend) half as much. And in theory, talking strain energy theory only, and not considering the dynamics at play, a stiff rod should cast the same as a flimsy rod.
But in reality, the dynamics (motion, mass, and resultant forces) plays into it to explain effects of stiffness on casting. If your rod “loads up” (bends) nicely as you’re about to cast, and through the swing of your cast that bend straightens out, you’ve gained extra motion of the bait through your swing. So you can get better acceleration of the bait. But the rod can also be too flimsy such that it is still greatly bent when you reach the point of your swing that the bait should “fly out”, and in that case, the stored energy in the rod didn’t transfer into launching the bait. Does that make sense?
And stiffness as it relates to sensitivity. This is simple, probably not worth explaining. A stiffer rod transfers the “feel” of bites, ticking weeds, blades stopping, etc. better to the user. It will drive hooks into the fish’s mouth better. But it won’t play the fish as well as a less stiff rod.
Back to the lever concept:
The length also greatly comes into play for stored energy in the bent rod (strain energy). The length actually has a CUBED effect on the strain energy. I.e., double the length, and you increased stored energy EIGHT TIMES.
So even though a longer rod makes you work harder to hold the bait up and requires more power from you to swing through the cast, its length really aids in the transfer of stored energy to the bait. Stiffness also plays a factor on the acceleration of the bait through the casting motion. You can’t go too flimsy, though, or the stored energy doesn’t transfer to the bait as well.
Obviously weight comes into play as you talk about long rods, but that’s pretty straight-forward, and you didn’t ask about that.
Hope that makes sense. Like I said, it sounds like you already understand the concepts and don’t really need layman’s terms, so the above includes a little more physics, dynamics, and deformable body mechanics.
Good questions.
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| Okay, I guess Chemi's approach was probably better. |
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Location: Smith Creek | jaultman - 4/17/2015 7:58 AM
BrianF. - 4/17/2015 5:33 AM
Who wants to tackle the questions posed above and put them in terms that layman like me can understand?
Brian
Now, when it comes to sensitivity, that long lever arm works to your advantage. A longer rod will magnify the “feeling” of bites, when blades stop spinning, etc. (all changes of line tension ) when compared to a shorter rod (as long as your rod isn’t pointed straight at the bait, because then, of course, there is no lever arm ).
Good reply except for this paragraph. Unless the long rod is exactly the same weight as the short rod this is false. Two factors for sensitivity are weight and stiffness. Decreasing weight and increasing stiffness will increase sensitivity.
Which is why a high mod (stiffer) carbon is more sensitive than a low mod carbon. Less carbon is required to achieve the desired stiffness on a high mod rod.
To the original question, and quite simply, more force is required to cast a longer rod but the results from that applied force are much greater than with the short rod.
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Location: Black Creek, WI | Good topic. To make things simple, I'll use the playground "see saw" example. Remember when you were kid and sat on the "teeter totter" with your buddy? If he was heavier than you, you needed to sit on the very end in order to try and raise him up. If you slid forward (shortened your lever) he had more "power" and you got raised up.
As we fish with longer rods, we are getting the shorter end of the stick. Meaning... we are giving the fish more power (the longer lever). the reel seat or wherever you hold the rod is the "fulcrum point"... or the point at which you measure the two different levers (yours vs the fish's end of the rod).
Adding a longer handle will give the angler the ability to add more power when needed... like for casting or figure8 hooksets.
When I first started using 9' rods and longer... I felt like I was "horsing" fish. This cost me a fair number of fish because I backed off on my pressure (too much in this case). Once I realized it just FELT like I was putting more pressure on the fish because the fish had the longer lever.... I started putting the screws to them and bagging more fish as a result.
Moral of my story? Longer rods require longer handles. |
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Location: Eagan, MN | Great reply jaultman!
My agenda with the original questions is twofold: 1) try to understand the relationship between lengthening the rod and power applied to a fish; and, 2) understand how the stored energy, and therefore fish fighting ability, changes with rod length. I probably should have said, "...all things being equal', because there are obvious factors that play into all this, like material stiffness and rod action.
Chemi's link had some interesting information, though didn't get to the heart of the questions. How much power do we lose on the business end of the line when moving from a 6' rod, to a 9' rod, to (potentially) a 12' rod? Assuming for a moment that a rod is a rigid lever, does the percentage increase in rod length transfer to an equal percentage decrease in lifting power applied to the fish? Or, is there a multiplier effect as with stored energy and changes in length as jaultman points out? That, by the way, was a brilliant observation I've never seen or read before. Could be the primary reason longer is better when fighting large fish successfully.
There is a part of me that thinks there is a theoretical optimal solution to the questions of rod length and action; at least in terms of seating hooks and fighting big fish successfully. In my mind and experience, longer has proven to be better. Yet, there has to be a point of diminishing returns. Yes?? I do want to explore the concepts of material/rod stiffness and rod action at some point though, since there seems to be a trend in bass fishing these days towards soft, long, parabolic action rods. Is this the next wave of the future in musky fishing?
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Location: Eagan, MN | Good point, JLong.
B. |
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| BrianF. - 4/17/2015 9:29 AM
Assuming for a moment that a rod is a rigid lever, does the percentage increase in rod length transfer to an equal percentage decrease in lifting power applied to the fish?
Brian
Exactly. This is what I meant by "inversely proportionate".
Teeter-totter is the qualitative example. Use a tape measure and some people whose weight you know, and you prove it quantitatively. |
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| jaultman - 4/17/2015 9:45 AM
BrianF. - 4/17/2015 9:29 AM
Assuming for a moment that a rod is a rigid lever, does the percentage increase in rod length transfer to an equal percentage decrease in lifting power applied to the fish?
Brian
Exactly. This is what I meant by "inversely proportionate".
Teeter-totter is the qualitative example. Use a tape measure and some people whose weight you know, and you prove it quantitatively.
I should actually clarify a hair further. The numerical percentage change isn't the same... it works like this:
If rod A is 50% longer than rod B (Length A = 3/2 * Length B), then your leverage with rod A as the user is two-thirds as effective as with rod B (User leverage effectiveness with Rod A = 2/3 * User leverage effectiveness with Rod B). So it's a 33% decrease in "power applied to the fish" (to use your words).
Rod's twice as long, fish owns you twice as hard. 100% length increase results in 50% decrease in effectiveness of your efforts in terms of leverage.
How's that for over explaining? |
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Location: Chisholm, MN | jaultman - 4/17/2015 9:52 AM
jaultman - 4/17/2015 9:45 AM
BrianF. - 4/17/2015 9:29 AM
Assuming for a moment that a rod is a rigid lever, does the percentage increase in rod length transfer to an equal percentage decrease in lifting power applied to the fish?
Brian
Exactly. This is what I meant by "inversely proportionate".
Teeter-totter is the qualitative example. Use a tape measure and some people whose weight you know, and you prove it quantitatively.
I should actually clarify a hair further. The numerical percentage change isn't the same... it works like this:
If rod A is 50% longer than rod B (Length A = 3/2 * Length B ), then your leverage with rod A as the user is two-thirds as effective as with rod B (User leverage effectiveness with Rod A = 2/3 * User leverage effectiveness with Rod B ). So it's a 33% decrease in "power applied to the fish" (to use your words ).
Rod's twice as long, fish owns you twice as hard. 100% length increase results in 50% decrease in effectiveness of your efforts in terms of leverage.
How's that for over explaining?
The great thing is that you just spit this stuff out without hardly thinking about it. I can't even read it I'm so dumb! |
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Location: Eagan, MN | jault, let me do that math on a somewhat more real life example.
So, back when I learned to musky fish, I was using a 6' pool cue rod (Rod B), and smashed them on a hookset for all I was worth. Let's assume I applied, say, 10lbs. of pressure for one instant on that fish with that hookset. Today, using a 9' rod (Rod A), and smashing them equally hard, I'm now applying 6.7lbs of pressure for one instant on that fish, correct? If I move to a 12' rod, then I'm applying only 5lbs. of pressure with the same hooksetting force? That doesn't seem like much force! The mitigating factor is that the stored energy in the rod is increasing at a rate that is cubed for each incremental increase in length. I think there is another mitigant.
All this leads to more questions that I think are relevant to how we fish. Are we penetrating bone, soft tissue, and cartilage with the power applied on the hookset with these long rods?? Or, is the much greater stored energy allowing us to grind hooks home as the fish thrashes?? What we aren't talking about is the effect of rod tip speed that occurs when a rod is lengthened. I think that rod tip speed is an under-appreciated factor in seating hooks past the barb and could very well be what is driving hooks home with these longer, less powerful rods. Think of it this way, you could drive a straw through a 2X4 if the straw was at a very high velocity. You see crazy things like this with tornado damage all the time in the news. Just like that straw through a 2X4, I would love to know what the relationship is to the rod tip speed as the arc is increased with the lengthening of the rod.
Brian
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Location: Eagan, MN | I think we are getting somewhere with all this, btw, and will try to summarize my thoughts after noodling this a bit longer. |
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Location: Smith Creek | is it easier to drive in a nail with a long handled hammer or short one? |
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| Flambeauski - 4/17/2015 10:47 AM
is it easier to drive in a nail with a long handled hammer or short one?
Different mechanics at play (no pun intended).
Is it easier to quickly back-swing the long hammer or short one? There's the question that applies (closer). |
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| Flambeauski - 4/17/2015 10:47 AM
is it easier to drive in a nail with a long handled hammer or short one?
In fact, why even throw in that example? It's so far off that it convolutes his question. The application in question is simple enough on its own:
Is it easier to pick up ten pounds with a long rod or a short rod?
(the weight is located a distance away from you roughly equal to the rod length) |
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| BrianF. - 4/17/2015 10:18 AM
So, back when I learned to musky fish, I was using a 6' pool cue rod (Rod B), and smashed them on a hookset for all I was worth. Let's assume I applied, say, 10lbs. of pressure for one instant on that fish with that hookset. Today, using a 9' rod (Rod A), and smashing them equally hard, I'm now applying 6.7lbs of pressure for one instant on that fish, correct? If I move to a 12' rod, then I'm applying only 5lbs. of pressure with the same hooksetting force? That doesn't seem like much force! The mitigating factor is that the stored energy in the rod is increasing at a rate that is cubed for each incremental increase in length. I think there is another mitigant.
The example is good except some word choices, but that's just getting nitpicky.
For what it's worth, I think most of us are capable of hitting the fish with 20 lb or more with even a 9 ft rod. You can make a tightened drag slip on a hookset, right?
Also, as your alluding to, there's the whole motion thing that comes into play. |
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Location: Eagan, MN | jault, can you put your mathematical mind to this question?
All other things being equal, what is the difference in speed at the rod tip assuming a 6' rod, 9' rod, and 12' rod?
This should keep you busy for a while, but I think understanding the change in rod tip speed with a change in rod length is going to be important to our discussion and conclusions. The formulas I found on-line were way over my head.
Brian |
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Location: Grand Marais, MN | long rod= loss of mechanical advantage of the class III lever. However, you have a slightly greater angle with a longer rod with respect to the horizontal plane where the fishes mouth is (which may help set the hook in certain instances).
now can we cover the "power" or "torque" or how much "work" it is to reel a reel? maybe for another day.... |
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Location: Smith Creek | I better leave this to the experts.
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| BrianF. - 4/17/2015 11:04 AM
jault, can you put your mathematical mind to this question?
All other things being equal, what is the difference in speed at the rod tip assuming a 6' rod, 9' rod, and 12' rod?
Brian
If you're just talking about input movement and resultant tip speed, it's extremely simple. You're 12' rod tip is moving [roughly] twice as fast as your 6' rod tip given the same input speed.
cork handle of the rod on your hip, both hands at the reel seat located one foot away from the contact point between your hip and the rod handle. Pull on the rod such that your hands move one foot closer to your body in, say, a quarter of a second. Let's say your hands traveled total 2 ft in total 1/2 second.
6 ft rod tip would have traveled an approx. 10 ft sweep path in that 1/2 second. 4 ft/sec input speed, 20 ft/sec rod tip speed
12 ft rod tip would travel 22 ft sweep path in that time. 4 ft/sec input speed, 44 ft/sec rod tip speed.
That's tangential velocity, meaning the speed along the sweep path. Those are not exact numbers, and the kinematics isn't exact because the motion isn't exactly circular. |
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| jaultman - 4/17/2015 10:54 AM
Flambeauski - 4/17/2015 10:47 AM
is it easier to drive in a nail with a long handled hammer or short one?
Different mechanics at play (no pun intended ).
Is it easier to quickly back-swing the long hammer or short one? There's the question that applies (closer ).
You can drive a nail much easier with a longer handled 20 oz framers hammer than you can with a 16 oz framers hammer with a shorter handle.
But you can swing the 16 oz hammer all day, and drive in many pounds of nails. The 20 oz hammer? Not so much.
I think for casting purposes, the rod tip is what makes the difference. That additional flex is what actually propels the lure rather than the force of you making your cast. Shorter rods, to me, are more work to cast.
The advantage of wide figure 8's and controlling the fish are easily seen. It's more difficult to turn them with a longer rod, but that extra foot of reach makes up for it.
When I first went from 7' rods to 8' rods and then 8'6" rods, it took some getting used to, and I did lose some fish. But the difference was apparent when I tried going back to a short rod. |
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Location: north central wisconsin | Jason, I really like the lever/see-saw analogy, as I've never looked at it that way before. However, in fishing terms, one has a hand in the mechanics of both sides of the lever(not just pushing on the butt of the rod). In terms of hooksetting, if one can pull a(lets say 40lb) weight just as fast with a 9' rod, as they can with a shorter one, wouldn't the longer rod win, because the weight was pulled further? I'd agree that exertion would be more with the longer rod used in lever terms, but wouldn't it equate to increased motion/success on the other end(Newton)? |
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Location: Land of the Musky | I thought I would never have to pull out my Calculus books again... |
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Location: Eagan, MN | Jason, the lever/see-saw analogy is a good one for understanding the relationship between power/load lifting capabilities and the length of a rod, but that analogy only addresses part of the whole story. A fishing rod is not exactly a lever/see-saw in that the rod is not rigid like a true lever and tends to also act something like a spring. That spring aspect is what has me thinking. The other factor that needs to be considered is how rod length impacts the speed of the rod tip, which may be an important concept when trying to understand how to get the most benefit out of these longer, less powerful rods.
Let me try to boil this down in a way my simple mind can understand. Granted that none of this applies to how well the rod works baits, casts, or figure-8's; and those are all legitimate issues for us muskyheads. However, the original question was trying to get at the heart of what's happening with the rod at the moment a fish strikes and the angler tries to drive hooks home and keep the fish pegged all the way to the net.
All other things being equal:
Rod Power: Longer Rod = Less Power, Shorter Rod = More Power
Stored Energy: Longer Rod = More Stored Energy, Shorter Rod = Less Stored Energy
Rod Tip Speed at Hookset: Longer = Higher Rod Tip Speed, Shorter = Lower Rod Tip Speed
So, what exactly is the factor that is setting the hook in a fish most of the time?? Due to the loss of power, we probably aren't muscling-in hooks with longer rods. Also, consider that as a rod gets longer more of the energy we are applying to the rod is being absorbed and stored. To me, what this points to is the importance of rod tip speed for setting hooks using longer, less powerful rods. My take-away from all this is that, in order to get the utmost fish-landing benefit from longer rods, we probably want to try to maximize our rod tip speed on the hookset. Or, in other words, a very fast sweep or snap of the rod at hookset is far better than a slow, sweep in which we try to muscle the hooks home.
Does the logic of the conclusion make sense? What's missing? Overly simplistic?
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| Flambeauski- so now I have to upsize my hammers to 9' ?
Gonna need a bigger toolbox... |
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| First, let me say that I'm really glad you started this discussion. I haven't really considered just how crucial our gear is when it comes to hooksets and playing fish in the way that I have now, and others' posts here have taught me new things, too.
Be careful when trying to attribute hook-set effectiveness to rod tip speed alone. Motion comes from force - not the other way around. I agree with you that a FAST hook set is very important, but rod tip movement (and resulting bait/hook movement) is still just a function of the input force and the properties of the gear.
The measurable, repeatable, dependable thing that causes a hook point to puncture a fish's mouth is pressure. Despite the many other uses of that word, it means force per unit area. That's one of the reasons you want your hooks to be as sharp as possible - to decrease the area of contact. Force comes from you and is transferred through your gear to the hook point in the musky mouth.
In my opinion, force is not the limiting factor when it comes to setting the hook. What I mean is, almost all of us fisherman are strong and fast enough to easily drive hooks into the mouths of muskies with almost any normally-used musky rod. But you have to consciously set the hook hard and fast, and your gear has to allow for quick generation and transferal of force.
As we all know, these things will detract from a good hook set: (a) stretchy line, (b) a weak rod, and (c) loose or bad drag. It is because the work you put into the hookset goes into storing (a and b) or wasting (c) energy, rather than applying force to that fish's mouth. |
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| BrianF. - 4/20/2015 1:55 PM
Rod Power: Longer Rod = Less Power, Shorter Rod = More Power
Stored Energy: Longer Rod = More Stored Energy, Shorter Rod = Less Stored Energy
Rod Tip Speed at Hookset: Longer = Higher Rod Tip Speed, Shorter = Lower Rod Tip Speed
Just a quick point - using "power" in the context above isn't really accurate. I only make this clarification because you're using other actual physics terms correctly, like "stored energy". I think what your saying is
Fisherman's Leverage: Longer Rod = Less Leverage; Shorter Rod = More Leverage
and that really clarifies your point, which is contrary to what some might think. You get LESS "payoff" against the fish for your efforts with a longer rod |
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Location: Eagan, MN | jault, I think you are right. The point I was trying to make was that the transference of force and the ability to seat big hooks past the barb is probably impacted by velocity or the speed at which that force is transferred. I don't plan to try this at home, but I'd be willing to bet you could take a large, sharp musky treble and apply, say, 5lbs of force to that hook very slowly with a line/rod/reel combo without penetrating the tough palm of my hand. Take that same hook and swing the rod, limiting the force to the same 5lbs at max, and chances are the momentum and velocity applied would require a trip to the ER. I'd love to do some experiments in this regard, though not with my hand. hah Maybe substitute cardboard or something.
Guess all I'm trying to say is we probably have not been thinking enough about rod tip speed (e.g. velocity and momentum) and how this plays into getting the most from these longer, less powerful rods. Absent hooks penetrating on the initial hookset, I don't discount that hooks often set past the barb by the grinding action of fighting a fish with a steady and forceful pull.
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Location: Black Creek, WI | Brian, 5 lbs of force is 5 lbs of force. Regardless of how you got there (fast or slow). The hookpoint doesn't know the difference.  That's why I focused on the Angler's leverage. The work the angler must put into the rod to achieve that 5lbs of force is dependent on the size of the lever. If you keep the same handle length on your rods... going to a longer rod means you must put more WORK into your hookset to achieve that same 5lbs of force at the hookpoint. Thus, if you thought you were hitting them hard with your trusty 7' Pool Cue... you gotta hit them even harder with your 9' footer. Where I struggled with was adjusting to how much pressure you needed to maintain a loaded rod (avoid slack line). This usually happened after the chaos of your initial hookset and at the point where you are trying to calm everything down and relax. A softer tip at this point is to your advantage, especially with longer rods. |
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