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## Loop morph & water tension

Moderator: Torsten

gordonjudd
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Location: Southern California

### Re: Loop morph & water tension

The shape's traces are in yellow, showing the evolution from a quite subtle initial bump.
and
What causes the overtaking though?
Dirk,
I see that as a transverse wave that gets larger as it propagates towards the fly end off the line and finally appears to turn into a loop as it reaches the end of the line. With no more medium to propagate in, it appears to disappear as the end of the line is pulled through the disturbance just as it did in Alejandro's early tail example years ago.

Thus it is just one more example of a dangle that starts out as a slight disturbance in the fly leg of the line. I have no idea of why the shape of that wave gets larger as it propagates, but it could be an effect of the tension in the fly leg going to near zero as you get to the fly end of the line. The linear mass density of the line would also affect the shape of the wave, but that is probably a secondary effect.

Gordy

Paul Arden
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### Re: Loop morph & water tension

I wonder if it’s the MED taper? I need to try this with a DT to eliminate that possibility. Interesting to find it inverted however, especially so because the dangling end S shape also comes from a similar angle change. Perhaps understanding the difference between the two would teach us something.

What I don’t understand – and I think this is the crux of it – is why the front of the wave starts to overtake… and then why this “loop” then “disappears”.

There is a lot I don’t understand actually But it also ties up into anchors and I think it’s very relevant.

Cheers, Paul
It's an exploration; bring a flyrod.

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gordonjudd
Posts: 1438
Joined: Sat Jan 19, 2013 11:36 pm
Location: Southern California

### Re: Loop morph & water tension

What I don’t understand – and I think this is the crux of it – is why the front of the wave starts to overtake… and then why this “loop” then “disappears”
Paul,
What is it that that you see the transverse wave overtaking? That wave is traveling towards the fly end of the line with a relative velocity going towards the fly end of the line that is equal to:
$$V=sqrt(T/\rho_{l})$$
Thus its velocity tends to go to zero at the fly end of the line as the tension goes to near zero at the end of the fly leg. Its shape also changes but I don't know how the shape is affected by the line tension or the linear mass density changes associated with the taper in the line.

Rather than getting frozen at the end of the line as you typically see with a dangle, the end of the line gets pulled through the loop at the end of that sequence and thus that loop formed by the transverse wave seems to disappear. That "disappearance" probably also happens with a dangle as the loop rolls out at the end of a long cast.

Gordy

Paul Arden
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### Re: Loop morph & water tension

Hi Gordy,

It’s this bit here that catches my eye…
5D519709-DF7A-4EF7-AB6C-F3C6C8C371FD.jpeg (23.27 KiB) Viewed 247 times
It initially starts from a direction change in the fly leg And yes it’s very similar to a dangling end on a distance cast where the line often travels through.

Thanks, Paul
It's an exploration; bring a flyrod.

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gordonjudd
Posts: 1438
Joined: Sat Jan 19, 2013 11:36 pm
Location: Southern California

### Re: Loop morph & water tension

It’s this bit here that catches my eye…
If you play the original video on a high resolution monitor can you see the shape of the leader in that frame? In that frame grab, that "dangle" looks somewhat like the tear shaped loop you see in high speed videos of cracking a whip.

It would be good if this video could be repeated at a 240 fps frame rate with a closer camera position (that would cover a smaller field of view) so you could see the shape of the line and leader when the transverse wave gets to the end of the line.

Gordy

Paul Arden
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### Re: Loop morph & water tension

Maybe it’s the compound front tapering of the MED. I’ll have to try it with a DT. If I shoot at 240fps it’s 1080 and not 4K. Just me in the boat this week however!

Cheers, Paul
It's an exploration; bring a flyrod.

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Lasse Karlsson
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### Re: Loop morph & water tension

I have seen it with other lines too, but only have a good example with a MED

Cheers
Lasse

It makes no difference at all whether you are in a fishing environment or on a casting court. Technique transcends all casting environments, irrespective of what, and where, those environments exist.

John Waters

Dirk le Roux
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Joined: Thu Sep 19, 2013 5:09 pm
Location: Pretoria, South Africa

### Re: Loop morph & water tension

Paul Arden wrote:
Thu Sep 30, 2021 6:37 am
Maybe it’s the compound front tapering of the MED. I’ll have to try it with a DT. If I shoot at 240fps it’s 1080 and not 4K. Just me in the boat this week however!

Cheers, Paul
Hi Paul

240fps is overkill on slomo. Better to go for maybe 120fps with higher resolution.

I doubt that specific taper plays much of a role, but let's see.

All the best,
Dirk