Trout Torque or Thoughts on playing fish

The effects of angles on torque and force, or what you really need to know about physics if you are to play fish more effectively

There is a little exercise that I have almost all of my clients experiment with on the river. It is a very useful one for everyone to try, if you wish to better understand what happens when you strike into a fish or are playing a fish. It also helps one better understand the forces that are applied.

The reason I do this is because we fish, for the most part, very small flies (#18 and #20) with limited hook holding ability and very thin nylon tippet, with limited breaking strain. Understanding how hard you can fight the fish is crucial in the battle between snapping off or landing the fish as quickly as practical.

The idea is that one person pretends to be the angler and the other pretends to be the fish. “The fish”, simply holds the fly or a knot in the leader between thumb and forefinger a couple of rod lengths away from “The Angler”. The angler holds the rod up at approximately 90° to the line and rotates it backwards with the hand as though playing a fish with a full bend in the rod.

The “fish” will notice that the amount of force applied is actually minimal, even though the angler is giving it his or her all.

Then the angler drops the rod tip towards “the fish” and applies the same rotational force (torque) and now “The Fish” can clearly feel the additional force produced. Dropping the rod further (increasing the angle) the force applied to the line is even greater still and usually at this point the line snaps.

(It is very valuable to then swap roles so that the clients get the picture of what it feels like at both ends, fish and angler) I have repeated this exercise with numerous clients and virtually everyone is astounded by how little pressure is applied when the rod tip is held high and the rod fully bent.

Experiments have shown that you cannot break 8x tippet (approximately 2lb breaking strain) with a #6 rod when the force is applied in such a manner, that is with a 90° angle between rod and line.

Instinctively we know that as the rod drops and the angle of attack changes so does the force applied, plus of course you lose much of the cushioning effect of the bend in the rod. In fishing situations this is often clearly demonstrated when the line snaps or the hook pulls out. Fishing for trout with light line, a high rod provides the least pressure on the tippet and hook hold, but fishing for GT’s in the surf (and using strong enough tippet to allow it) it is far more effective to play the fish with the rod tip low and the angle wide, providing maximum pressure on the fish.

 

But what really happens to the force on the line as the angle changes, and anyway which angle?

Which Angle?

I was wondering which angle was the important one in terms of working out the force and torque; in the above diagram is it angle A, B or C?

It turns out that if you solve the force for a set torque, you can solve for B or C and get the same answer. I am very grateful to Gary Glen-Young here, because he has a superior mathematical brain to mine and helped check the figures, he suggested that there may be potential error but it turns out one can solve for either angle and get the same answers. (Technically, if you want the least pressure on the line, the ideal position would be to have angle C at 90 degrees)

If in the next diagram I solve for both angle B and C, I get the same answer so in essence it doesn’t matter which one you use. The angles are different but so are the lengths of the “ imaginary rods” in the equation.

AngleCalculations

Solving for Angle B (45 degrees)

Force = Torque /( sine Θ x Effective Rod Length) = Torque/ (0.70710678 x 3) = Torque/ 2.1213

 

Solving for Angle C (90 degrees)

Force = Torque/ (SineΘ x Effective Rod Length) = Torque/ (1 x 2.1213) = Torque / (2.1213)

 

 

For most of this article I have solved for angle A, simply because it made things easier, if when you are fishing you think that imagining the angle C is better for you, that’s just fine, makes no difference. Just note that for angle C, the imaginary rod extends from your hand directly to the rod tip, it isn’t the angle of the rod tip itself that’s important.

It is worth noting that the rod/line angle can change for a number of different reasons.

The angle the rod is held

The distance to the fish (amount of line out)

If the angler extends his arms upwards

The length of the rod

The effective length of the rod (Bendiness of the rod if you will)

For any given rod position, the rod / line angle increases as the fish gets further away, decreases as the fish gets closer.

 

Roughly speaking, if you drop the rod from perpendicular to the line, to 45° and maintain the same rotational force with your rod hand, you increase the force on the fish by around 40%. But the maths can be deceiving, initially loss of some angle say from 90° to 80° doesn’t make a lot of difference, but the figures are not linear. For every degree of angle lost the additional force that you are applying gets rapidly worse.

Entering dangerous ground because I am a long way from a mathematician, but I am going to do my best to explain what goes on.

The first obvious thing to me is that (and for the present we are going to forget that the rod bends),  the longer the rod the greater the leverage disadvantage to the angler.

If you can only apply so much rotational force (Torque) to the rod handle with one hand the longer the rod the less force you are able to apply to the line.

So firstly, what happens to the pressure on the line, given the same torque but different angles?

What the graph demonstrates is that the relationship is not linear. The blue line shows percentage increase with changing rod /line angles. As that angle moves away from  90° it initially doesn’t make too much difference to the force applied to the line, but as the angle changes more, the change in force on the line jumps up exponentially for the same torque. By the time the rod is near to pointing down the line the force applied has almost doubled.

What does that look like in real life?

 

What does that look like in table form?

The table below uses a rod length of ten feet (3.05 metres), (rod bend is ignored for the purposes of this table). Torque has been set at 10 Newton Meters (Experimentation with two different lengths of rigid pole suggested that the maximum torque I could generate with one hand was between 10 and 11 Newton Metres. The force on the line has been calculated based on the equation F= Torque / (sineθ x Effective Rod Length (d)), where d is calculated as sine of the angle multiplied by the rod length.

Whilst the change in force was expected the numbers seemed low, it would mean that you could barely break 7x (about 3lb BS) tippet with a ten foot rod, held at almost any angle. It didn’t make sense, even though I know that breaking line when using the rod properly is pretty hard.

So I re-ran the calculations for my 9ft four weight (because if I busted it whilst experimenting it wasn’t such a big deal as some of the other rods).
If my 9ft four weight didn’t bend I would get the following table.

As expected the slightly shorter rod provided more pulling power, but still barely enough to break 7x tippet, how could that be? So I went out into the garden and bent the four weight about as much as I could with one hand. Roughly measuring the deflection I got a nominal rod length when fully bent of only 1.6 metres.

So I ran the table again, using a nominal rod length of 1.6 metres and a torque of 10 newton metres, this is what that looked like:

The force numbers had now climbed even further, ( almost double compared to the figures for a rigid rod) , and it would seem that even then if I was really pushing  things , with the rod at 90 degrees to the line I still wouldn’t be able to break 7x tippet.

Not entirely trusting my limited maths skills  I took the #4 weight into the garden, rigged up and pulled, it turned out I couldn’t break the line, not with the rod at 90 degrees to the line, not even at 120 degrees to the,  in fact I couldn’t break the tippet even if I dropped the rod and opened up the angle to 150 degrees.

So the next step was to unleash my 9 ft #10 weight rod, dusted it off (it hasn’t seen water for a while), and rigged that up.What would you know? Keeping a good 90 degree angle between the line and the rod I gave it my all, and guess what? I simply couldn’t break the tippet.

With me, sometimes things can get a bit silly and I just couldn’t believe the numbers, so I figured if I was right I wouldn’t be able to break 7 x (3 lb) tippet with a broom handle, yes a real one with the brush on the end. As it turned out I could break the tippet with the broom handle, JUST!!

But look at the numbers, the broom handle from tip to my hand was about 0.8 metres, according to my tables then I should get a maximum force at 90 degrees of about 12.5 Newtons or 2.8 pounds. I did break the tippet but had marks on my rod hand from doing so and I think that the result was more a function of the short length of the handle than its stiffness. The point is that leverage, rod bend and rod length seriously affect how hard you can pull on a fish, and that is not anywhere near as hard as most of  us assume.

 

Bear in mind that these figures are estimates, I don’t know exactly how much torque you can apply to a fishing rod for sure, the 10 Newton Metres seems a fair estimate based on my experimentation, and I think that it does serve to offer a picture of what happens when you are playing a fish and probably gives a reasonable guideline as to where you want to be holding the rod  if you are trying to protect fragile tippet, or for that matter if you are trying to apply maximum force.

So let’s look at a typical on stream scenario. Our happy angler hooks a fish, it isn’t too far away . Our angler is giving it his all holding the fish, but the pressure he is applying is well within the bounds of his tippet strength.

But now the fish makes a run for it, instead of giving line the angler holds tight, as he is already applying the maximum torque that he can, the only option is that the rod gets pulled downwards, increasing the angle θ.

The pressure on the line, without the angler feeling anything different has jumped from 0.75 lb to 0.899 lbs. That’s a 20% increase but of course he is still well withing the breaking strain of his gear. and remember that as far as the angler can feel he is applying exactly the same amount of torque.

 

Determined not to lose the fish he gallantly holds on, remember that he is incapable of applying more torque with his one hand and if the fish runs further the rod will inevitably be pulled down and the angle will become even greater.

Now things are getting more risky and heading for disaster fast, the pressure on the line has jumped from an initial .75 lbs to 1.47 lbs, (pretty much a 100% increase) and yet to the angler it feels as though he is applying the same force, remarkably even now the tippet isn’t bound to break , but a sudden pull dragging the rod down a fraction more and it is likely the tippet will break.
What would have been a better option would have been to let line slide through  his fingers of off the reel (assuming the drag isn’t set too tight) and reset the angle of the rod that would offer more protection to the tippet..

Bear in mind that for ease of calculation the above figures assume that the rod doesn’t bend, in reality the figures are likely to be about twice as high if the rod bends fully.

Keeping the rod up is an overly simple answer:

As a young angler I was always told to “keep the rod up” or “give it the butt”, but depending on the situation the high rod tip isn’t necessarily the right answer.

Let’s think of another scenario, you are now fishing from a boat, you hook a fish and it starts to dive.

Initially the rod/ line angle is 50° and you are still in a fairly good position.

 

Determined to keep the rod up you allow line to slip through your fingers as the fish heads for the depths, diving beneath the boat.

But our angler has made things worse, the acute angle of the line to the rod means that pressure on the line will jump the moment he grabs the line, plus he has given up almost all of the shock absorbing benefits of the rod, he will most likely lose the fish.  Even had he held on tight and simply allowed the rod to be pulled down he would have been better off.

In this instance, allowing the rod to be pulled down is an advantage, because it has improved the angle of line to rod and reduced pressure on the tippet. So each scenario has to be assessed based on the angle of the rod to the line and not a lot else. That may mean giving line, or it may mean hanging on.

NOTE: Up to this point all the diagrams and calculations have been based on the rod not bending. Of course in real life the rod does bend, and we shall see that when the rod bends the force applied to the line will be higher, even considerably higher depending on how much the rod does in fact bend. So the figures above are not real, but they offer an illustration of what happens when rod angles change. Paradoxically these figures also show that but for shock, on a steady pull you wouldn’t be able to break the lightest nylon on a really stiff pole. 

What about rod bend?

As the rod bends it shortens the effective rod length this has an effect on the force applied by the same torque, contrary to what you might think, the force on the line jumps up.

One instinctively imagines that a softer (more bendy) rod, will land fish less quickly and apply less pressure than a stiff one. That is at least what a lot of people seem compelled to discuss when they see anglers with lightweight gear. People will tell you that it is “unsporting” or “unfair” to fish with gear that they consider “too light”. These calculations suggest that this is fallacy , you are likely to be able to put more pressure on a fish with a shorter more bendy rod than with a long stiff one (assuming that you keep the same angles)

I suppose that instinctively we understand that the longer the effective length of the rod,( and recognizing that the more a rod bends effectively the shorter it gets) we can see that you are at less of a leverage disadvantage with the shorter rod and thus should be able to apply more force. That is borne out in the calculations.

If Force= Torque/Length, the effective shortening of the lever would give one more force on the line.
In the diagram below I have simply assumed the rod angle that provides the least force for a given amount of torque, that is an angle of 90°.
In the first instance the rod is assumed not to bend at all and has a length of 10ft (3.05 metres)
In the second scenario the rod bends reducing its effective length by 1.1 metres, that has the effect of increasing the pressure applied for the same torque by pretty much 50%.

Let’s look at a couple of examples to be sure that the same is true with the rod at more of an angle.:

What if we solve for the alternative vector, between the butt and the rod tip, will we still get the same answer?

Solve for alternative vector d and alternative angle x

So we get the same answer, higher than with an unbending rod, but still quite a moderate amount of force,given that we do break tippet when applying maximum force, particularly at low rod tip positions it can only be that the rods are perhaps bending more than we imagine.

If that is true, and I am pretty convinced that it is, then softer more bendy rods actually allow you to apply more pressure than stiffer ones, with the added advantage that being more flexible they also offer better tippet protection in the event of sudden surges from the fish.
In other words, were tippet strength not an issue, you could apply far more pressure with a short soft actioned rod than you could with a long stiff one.

To my mind, there are two significant things which affect how much pressure you can put on the fish, the limitation of the amount of torque you are capable of applying and the tippet strength. We have seen, from the calculations earlier on, that you can apply almost any amount of pressure depending on at what angle the rod is to the line. If you are a relative weakling and can’t apply much torque you can change that angle to put more pressure on the fish.  If you are a bit of a bully you can keep the angle close to 90° and stop yourself from popping the tippet. So the real limit, given that you understand the physics, is simply the strength of the tippet.

One can see that in real life, a trout angler with 8 x tippet will play fish with the rod at a close to 90° angle. Someone battling a Giant Trevally on the flats, with 150 lb test leader, will be incapable of holding the rod at anything but the shallowest angle and will be able to apply maximum pressure with the rod low because the tippet will take the strain.

Below is a chart based on a torque of 10 Newton Metres with varying rod lengths, that could be actually shorter rods or rods that become effectively shorter because they bend. Either way, rather like the first table, the results are quite remarkable, relatively small changes in rod length make for relatively large changes in pressure applied. In reality, shorter rods behave in exactly the same way as changing rod angles, the reduction in the “effective length”  of the rod provides more force on the line for the same amount of torque on the handle.

 

Final conclusions:

In reality the amount of torque we can apply through the rod handle is limited (assuming you are using one hand).

Control of the amount of force on the line then is limited to the angle of the rod to the line

To protect fine tippets it is best to keep the angle as close to 90° as possible

To apply maximum force, if your tippet will allow it, it is better to have the angle far more oblique.

Softer rods actually allow you to apply more force for the same rod angle because they bend more and get effectively shorter.

Long stiff rods allow you to apply less force than short or softer ones for the same rod angle.

There is no reason to suppose that softer rods apply less pressure or tire fish less effectively than stiff ones, in fact it seems likely that the opposite is true. In a practical sense, not only do you apply more force when the rod bends, but you have more cushioning from sudden shocks, so you can operate closer to maximum without breaking the nylon.

You can apply more torque and thus more force if you move you hand up the rod (take care you don’t break it).

You can also add more torque and thus force by using both hands, transforming the leverage effects and the torque applied.

You will also add more force if you use a fighting butt because you change the leverage effect.

You should be extra careful when the fish is close (during netting) as chances are force will increase and the hook hold may pull out.

The real limitation of how much pressure you can apply fundamentally lies with the tippet strength.

If all of the above is true, why is it that we still on occasion break off fish?
I can only think that the main culprits are:

Shock and inertia on a sudden take
Allowing the rod tip to be pulled down
Poor knots, wind knots and such.

There seems to be plenty of evidence that using the rod properly it should be almost impossible to break off fish on even light line, and suggestions that one cannot play fish as robustly or land them as quickly with light gear don’t seem to hold true. What is true , is that at the end of the day your tippet strength is the single most important factor in how much pressure you can actually apply to a fish.

Brought to you by Inkwazi Flyfishing Cape Town’s best fly fishing guiding service.

 

 

 

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3 Responses to “Trout Torque or Thoughts on playing fish”

  1. Craig Thom Says:

    I completely get what you are torquing about. Brilliant

  2. paracaddis Says:

    Thanks Craig, glad that you enjoyed it

  3. Line Control | The Fishing Gene Says:

    […] a previous post “Trout Torque” I discussed in depth the pressures and forces applied when playing fish. You are recommended to […]

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