The point of tapers in fly lines and leaders

[Graeme H]

If we have the same head length but make the front taper very long (pictured below) we have a different style of cast available to us. Carry is again limited by the head length, but the amount of "overhang" we can use now has a very small range. That thin running line won't be able to make a good loop shape in the line's belly, so to cast this line for distance, we need to make sure the belly and rear taper are just outside the rod tip. We may not be able to shoot very far, but as soon as we start the line turning over, the "ball canon" effect will drive the loop all the way to the end with little effort. But the MPU at the last third of the line is small, so only a small fly can be delivered. That small fly will be delivered delicately!

It's also harder to shoot much line until much more line is outside the tip.

On the plus side, this line is wonderful for roll casting at any distance and is perfect for spey casting. Lots of mass at the top of the D loop can be used to turnover the remaining front taper just like the ball canon.

Cheers,
Graeme

[Will]

Cheers Graeme, very useful diagrams.

I’d like some clarification on the difference between “rotational speed” and the speed imparted to the fly leg by the casting stroke, and its impact on the loop. Presumably if rotational speed slows below the speed of the fly leg, you get a disturbance in the loop shape (dolphin nose?)?

Also, some clarification on why, if the line had no front taper (E), it would kick over, whereas with a front taper (which we’re saying is accelerating the fly leg) it doesn’t? I can’t help thinking that the front taper has some role in slowing turnover at the very end, and stopping the “bulb” kicking down.

Cheers!

Will

[Graeme H]

Rotational speed of the rod? That itself doesn't have an impact on the loop shape. Rotational speed of the rod adds to the final speed to the tip before the line overtakes the tip to form a loop. The tip keeps moving away from that point and widens the initial loop. How far away it moves is up to the caster and his/her rod control.

Minimising counter flex makes a narrow initial loop (that may further narrow). Maximising it makes a wider loop (that may also further narrow). Excessive rotational speed almost necessitates a large counter flex because we can't stop the rod quickly enough to reduce it.

The dolphin nose is not related to the rod's path. You can see them developing in the video of the line crashing into the net: no rod required!

You can see the effect of insufficient reduction of line mass (e.g. as with no front taper) at the 18 second mark in the video I posted on the path of a point on the line (posted again below). On the day I shot that video, I was trying to capture how tails tie knots in leaders. I had a short leader of some sort of monofilament line tied to an 8wt line. The butt section of that leader is not heavy enough to provide a smooth transfer of energy from the line to the leader and it kicks wickedly after the loop hits the leader. To avoid that, I needed a heavier butt section or a longer taper in the line (to a finer line tip). If the total taper (including fly and leader here) was longer, the energy would have been smoothly dissipated by the end of the cast. The air resistance of the fly would have overcome the force of the leader pulling the tippet.

"The Bulb" is out of play once the front taper passes into the loop. It's already in the rod leg.

Cheers,
Graeme

[Paul Arden]

It would be nice to have some short answers that we can agree on. For example:

The front taper achieves this ... because of this ...
The TT taper achieves this ... because of this ...
The MED taper achieves this ... because of this ...
When heavier line reaches the loop this ... happens because of this ...
When lighter line reaches the loop this ... happens because of this ...

It’s dark but I’m going to have some dinner and find some street lights to cast under.

Cheers, Paul

[Graeme H]

Actually, there's something else of interest in that video, and at the risk of complicating things further, I'll draw your attention to it. This line is a Rio Versatip line. It has an interchangeable front section, allowing quick changes between floating, intermediate and sinking tips to be used.

At the 9 second mark and again at the 31 second mark, the joining welded loops pass through the cast loop. They have a bit more mass (MPU) and they are a bit stiffer than the rest of the line and you can clearly see waves in the rod leg generated by the uneven mass hitting the loop. At 31 seconds, the mark at the bottom of the loop pauses its downward drift as tension in the rod leg momentarily increases.

In every one of my videos with this line, this can be seen if you're looking for it. Maybe I should put some unmatched sections on and video the results.

Cheers,
Graeme

[Graeme H]

It would be nice to have some short answers that we can agree on.

Fixed it for you Paul.


(I'll put something together that I can agree on. Might take me a day or two to make it short though. )

[Will]

Hi Graeme

Apols. I wasn’t clear on my question.

I wasn’t talking about rod rotation at all.

You said in post 20 “ It can't transfer its energy as efficiently into A so the line in the rod leg (labelled "Running line" above) gets tighter and rotation is slowed a little.” (My bold). I assumed you were talking about the speed at which the line rotates (travels) around the loop, and wondered how that related to the speed of the fly leg. Presumably if the line speed in the loop slows below the speed of the fly leg, you get a disturbance in the loop shape (dolphin nose?)?

On the issue of stopping the line kicking, you said in post 23 :
“The butt section of that leader is not heavy enough to provide a smooth transfer of energy from the line to the leader and it kicks wickedly after the loop hits the leader. To avoid that, I needed a heavier butt section or a longer taper in the line (to a finer line tip). If the total taper (including fly and leader here) was longer, the energy would have been smoothly dissipated by the end of the cast.”

I guess I’m struggling with how the front taper can both speed up the final portion of turnover and dissipate the energy to get a soft turnover at the same time... surely if energy is being dissipated, then the line should slow?

Really sorry if I’m being thick here.

Ta!

Will

[gordonjudd]

I assumed you were talking about the speed at which the line rotates (travels) around the loop, and wondered how that related to the speed of the fly leg.

Will,
In the case of a tethered loop the speed at which the line rotates (travels) around the loop (v_tangential) is one half the speed of the fly leg. It has the same value as the speed of the loop over the ground(v_loop).

In general If v1 is the speed of the fly leg and v2 is the speed of the rod leg then v_loop=1/2(v1+v2) and v_tangential=1/2(v1-v2). Thus the tangential velocity will decrease when you shoot line (positive v2 value) and will increase when you pull back on the rod leg (negative v2).

I guess I’m struggling with how the front taper can both speed up the final portion of turnover and dissipate the energy to get a soft turnover at the same time

I don't think it does cause the fly leg to speed up. In fact it causes the acceleration of the line to be reduced and thus reduces the velocity of the rod leg with time.

The tension at the top of the loop that provides the positive acceleration force on the fly leg equals rho_l (the linear mass density of the line)*v_tangential.^2. Thus when the line is thinner and rho_l is reduced the acceleration force will also be reduced and the velocity of the rod leg will be slowed to reduce the tendency of the line to kick over as it does with a level line.

The fact that the drag losses increase exponentially (v.^2 in this case) with the line velocity is true, but the positive acceleration factor also varies as the square of the velocity so one factor does not have an inherent advantage over the other in relation to the velocity. At the end of the cast the line is short so the drag losses are also small, thus I think it is the decrease in the rho_l*v.^2 acceleration factor that dominates the final roll out of the loop.

As Lingard says:

A distinct acceleration phase is encountered later in the flight which, in the case of the level line, is sustained to the end. The double taper line, however, attains a sharp velocity maximum and then decelerates finally as the effect of the taper is felt over the last few meters of the cast.

Gordy

[gordonjudd]

So is the taper on the bullwhip making it harder to crack?

Paul,
No. The moving mass in a whip wave is concentrated in the tear-shaped loop that is running down the whip.

Because it's linear mass density is so high it is not affected by drag forces the same way a light fly line is. Thus a tapered whip is easier to crack using a whip wave since it has different energy considerations than a fly wave,

I think a tapered whip is harder to crack using a fly wave shape where the trailing end of the whip is traveling at twice the velocity of the u-shaped fly wave. I have never been able to get a crack using a fly wave in a tapered whip but experts such as Adam Winrich are able to do it.


I asked Winrich if he could crack a level whip using a whip wave, but he responded that he was not aware of anyone making such a weird whip.

Gordy

[Graeme H]

I wasn’t talking about rod rotation at all.

You said in post 20 “ It can't transfer its energy as efficiently into A so the line in the rod leg (labelled "Running line" above) gets tighter and rotation is slowed a little.” (My bold).

Ah, got ya. Sorry, I picked the wrong option ...

From what I can see in the videos with the marked lines, the only part of the line path that is curved* is the top leading edge of the loop. That little section is the only place in the line's path where the rotation occurs.

We can modify the amount of line following a curved path by adjusting the tension in the rod leg with our rod tip.

Presumably if the line speed in the loop slows below the speed of the fly leg, you get a disturbance in the loop shape (dolphin nose?)?

Presumably, yes. I need to study that some more though. (More video analysis. Yippeee! )

I guess I’m struggling with how the front taper can both speed up the final portion of turnover and dissipate the energy to get a soft turnover at the same time... surely if energy is being dissipated, then the line should slow?

The "at the same time" bit is where the issue is. It doesn't happen at the same time in one cast. If we pull back on the rod leg, we can momentarily increase the speed of the taper and leader going away from us. If we push forward on the rod tip (reducing tension in the rod leg) we can let the energy wipe off the taper.

However, this only works properly if the cast was not overpowered in the first place. An overpowered cast will still kick a bit, but not as much as if there were no taper on the front.

I think Lee's videos are wonderful examples of how the taper is performing. Frame-by-frame advancing lets us see a perfect comparison of two taper designs in action.

Cheers,
Graeme

* In a "normal cast" where the rod leg is not moving forward or back