Some thoughts on Bernd's thoughts on stretch in fly lines

[Paul Arden]

Hi chaps,

Not only do you need to know what force is required to set the hook under the specific circumstances but also if the rod is being used to set the hook because that’s also going to have an effect. 1.8KG at 90 degrees is a hell of a pull on most rods and usually sees the rod bend to a point that I for one would not like to go past!!! I certainly don’t set on trout with that sort of pull. Different in the tropics and I was playing with the spring balance and my initial set here might be around twice that. I’ve certainly measured pulls in excess of 10KG but not on the set. The set for me is more of a feeling thing with some fish here, a bit like Gary describes with Tarpon. Although if I set like that with poppers and Jungle Perch then I miss them all. I have absolutely no idea why.

It raises the question why does strip setting with dry flies usually result in a missed or quickly lost fish? And then when you try striking with the rod when moving the fly you normally miss the fish? Or at least that’s how it works for me, although I notice that spin anglers can often be quite dramatic with what they are doing. That could be the three trebles they use of course.

I had a hell of a job setting on Sailfish this time last year. Have to allow them to eat the damn thing and then, while they were running, try to get a few solid strip sets in. Really quite frustrating.

Very interesting thought on the recovery of the stretched line after the set, Merlin. That could indeed be really quite significant.

As far as altering strikes between fish, I’ve been learning to do this. For the past few years I’ve been really focused on my striking with Snakehead. Generally however I need to decide what I’m going to do before it happens. But I know that will change and I can feel it changing. It’s almost like time is slowing down during those moments. And I think it does because when I play it back in my mind afterwards it’s always in slow motion.

Cheers, Paul

[gordonjudd]

I can already set a hook by lifting the rod tip and a #5 fly rod has a stiffness of ~1 N/m; 1m fly line with 5% stretch @1,8kg has a stiffness of over 300N/m.
and
Not only do you need to know what force is required to set the hook under the specific circumstances but also if the rod is being used to set the hook because that’s also going to have an effect.

Gents,

The line spring constant depends on the length of course, so 10 meters of that 5% line would have a spring constant value of around 35 N/m. That is still much larger than the spring constant of a rod so I would think the line stretch would only come into play when the rod is pointed at the fish and a strip strike is used to set the hook.

I found that lifting the rod to set the hook is a hard habit to overcome for most experienced Trout fisherman. I got a lot of disgusted looks from guides when I instinctively raised my rod tip in reaction to a take only to watch the fish bolt away.

Gordy

[gordonjudd]

The 0.5 Gpa material would give approximately 5% stretch for a 1mm diameter line pulled by a 1.8 kg load

Merlin,
How did you calculate the Young's constant for a 5% stretch on a 1mm diameter line for a 1.8 kg load?

If I assume the Young's constant is equal to the stress / strain then I get:
\(E_l=1.8*9.82/(\pi*1.e-6*.05)\)
Which equals .112 GPa.

If I use the simple model to compare the spring force at the end of a 10 m line having (1% stretch for a 17.6 N force) for a finger acceleration of 8 m/s.^2 I get this curve. The constant 8 N force from the non-extensible line is shown in green.

Force_curve_p01.jpg (41.29 KiB) Viewed 1430 times

You can see the force from the stretchy line equals the force from the non-stretch line at around .125 sec.

Is that the criteria you used to compute the lag times shown in your table?

Gordy

[gordonjudd]

If I assume the Young's constant is equal to the stress / strain then I get:
El=1.8∗9.82/(π∗1.e−6∗.05)
Which equals .112 GPa.

Daniel,
I see that I used the diameter rather than the radius in that area calculation, so the expected modulus would be the .45 Gpa value you calculated for a radius of .5mm, higher than that if the the diameter was smaller.
Gordy

[Mangrove Cuckoo]

When considering hook setting I have always held a simplistic view of the main challenges. It is probably overly simplistic?

On one hand there are fish with tough mouths and you are using thick gauge hooks that commonly have barbs on top of that. The good news is you have relatively robust leaders and there is no reason to hurry. So you drop the rod and try to come tight.

On the other hand, the fish have delicate mouths and the hooks are incredibly thin, with laser sharp tips, and commonly no barbs. The bad news is the leader tippets are delicate and the fish can reject the fly quickly. So, you must get tight quicky but try to not break off. So, you lift the rod to protect that tippet.

Isn't that the case?

Trying to "set" a thick hook with the top end of a flyrod makes about as much sense as trying not to break a light leader with a strip strike?

[Merlin]

striking scheme.JPG (24.44 KiB) Viewed 1349 times

In practice we can use three springs as we strike or pull on a fish: the leader, the line and the rod. Roughly speaking one can estimate the overall spring stiffness like that (below “spring” must be understood as the stiffness in the direction of the pull/strike):
1/overall spring = 1/ leader spring + 1/ line spring + 1/ rod spring

In other words the overall stiffness is dominated by the softest element and it is always the rod (1N/m for a trout outfit to 3 N/m for tarpon rods). Depending on line length and material we can face 20 N/m to 160 N/m line stiffness typically. Finally the leader stiffness can vary between 12 N/m (light outfit) and 1200 N/m for a tarpon leader.

If we consider tarpon fishing, despite the apparent stiffness of the rod, we have to skip the rod to get a significant force on the fish (e.g. 1.8 kg peak force on a 5 kg fish) by pulling directly on the line to set a large barbed hook in place. The delay is less than 100 ms (not including the delay of reaction from the fisherman).

For freshwater trout fishing, skipping the use of the rod can put a rather large force on the fish and stress the leader. On the contrary, using the rod can protect the leader and is enough to set a thin sharp hook in the fish’s mouth. The delay is about 200 ms (not including the delay of reaction from the fisherman).

All is possible in between the two options (more or less low rod, more or less pull from the line hand).

Merlin

[Paul Arden]

I mostly agree Gary, 95% anyway, but I think there is something else to it as well. With the same fish (I’ll pick trout as an example, only because I know them better!) I point the rod down the line to set with streamers and lift the rod to set with dries.

Strip setting static dries on this fish (and any fish species, I think?) usually results in a missed fish. In this case we’ve removed the fish mouth hardness variable (same species) and we’ve also removed the hook thickness variable, because we are comparing different strikes with the same hook.

I think the difference might actually tied up partly with allowing the fish to actually eat the fly in the first place - ie timing - but also how we hook them, ie do we hook them by striking or instead keep tension allowing them to (initially or partly) hook themselves? If a fish takes a streamer static, for example, then I lift the rod to set… albeit more usually, shotgun style.

I miss a lot of fish because they haven’t closed their mouths or… sometimes, maybe… because they haven’t expelled water from their gills… I do think there are different eats in this equation.

Do Snook ever eat something from the top? Will they eat a small teased popper for example? Or a terrestrial?

This is an important topic for me, because I’m really struggling with hook sets at the moment! I’ve been exploring this for a few years now as you know. And on a fishery where the difference between a great day and no day is one fish it makes a difference!! Today was one such day. One eat, no fishy. Yesterday on the other hand was one eat, one fishy

Cheers, Paul

Edit: rereading my post makes me think that one of the bigger factors is whether the fly is moving or static on the eat. I know I base my strike differently on this. One of my biggest challenges with Snakehead has been very tough and is trying to give them slack after they’ve eaten a moving fly… and then setting. This is currently what I’m learning and have been for several years now. At the moment it’s like delayed rotation.. later and later and later

[gordonjudd]

The delay is less than 100 ms (not including the delay of reaction from the fisherman).

Merlin,
Did you use the simple finger/spring/marble model to come up with that delay estimate?

I get a much longer delay (286 ms) for the force from the spring to cross over the force from a non-extensible string for a spring constant of 160 N/m, acceleration of 3.5 m/s.^2, and mass of 5Kg as shown below.

1%_161_force_curve.jpg (41.87 KiB) Viewed 1303 times

Or did you mean a 1.8 N force instead of the force from a 1.8 Kg hanging mass (17.6 N force) used for the German club's measurement of stretch? That low force does appear to be applied at around 85 ms.

Gordy

[Mangrove Cuckoo]

Paul,

Yes, snook will eat a popper! Actually, it is probably the most fun way to fish for them. They are quite famous for their noisy take and resulting bubble ring shaped "rise". They have large mouths and are pure vacuum feeders... their distinctive "pop" can be heard from quite a distance.

The smaller fish a real aggressive and are real suckers for a popper. Unfortunately, the bigger they get the less likely they are to attack a flyrod-size bait. A large hard plug walking on the surface, cast on conventional tackle, will get the bigger ones to act like fools though.

On fly, big hooks / tough mouths... so coming tight with a straight line is best. The tough part is they often continue to move forward after the take. And that means you have to keep stripping. It is called a "is he there" strip and you don't attempt to get tight until the answer is yes.

By far the most difficult part of this technique is keeping the rod down. Everyone wants to raise the rod to remove the slack, which is counter productive in many ways. The better technique is to shove the rod tip into the water so tension can be retained.

I'm pretty sure I saw in one of your videos a snakehead dive toward you and under the boat after the take? Do they always do that?

[Mangrove Cuckoo]

Paul,

Hooking fish on streamers can be a lot more complicated than first glance, I think.

Most of the time, at least for me when fishing in the Everglades back country, the system is rather static: I am stationary in a canoe and the fish are stationary in rather dead water. If either of us is moving it will most likely be a slowly cruising fish. So, the "equations" are rather simple.

But not always. The more complicated situation involves current. In this case, usually, I am again stationary at anchor and the fish are stationary, but facing into a current. So, presenting the fly is much like swinging flies downstream. The take is usually unseen in this case as the waters are dark, so it has been difficult to actually see what is going on. But I suspect a lot can be learned from trout or salmon anglers swinging flies.

So, I am actually quite interested in what technique trout /salmon anglers employ when swinging flies in currents?

A third situation has come up over the last few recent seasons where the variables are somewhat convoluted. The fish are stationary and the water has little movement, but I am casting from a canoe that is being moved, sometimes briskly, by the winds. This situation allows a lot of water (and therefor fish) to be covered, but my hook up ratio is dreadful. I at first thought it was similar to swinging flies, but on second thought it really isn't. I have no clue on how best to handle this "hook up" challenge... yet.