Funny looking loop

Marc LaMouche · Post by **Marc LaMouche** » Fri Oct 05, 2012 9:07 pm

Paul, we still don't know if this cast was intentional or not.

Grunde ?

alp · Post by **alp** » Fri Oct 05, 2012 9:12 pm

Photo of funny looking loop cut from this video:

http://www.youtube.com/watch?v=NtHOuwInDRo

VGB · Post by **VGB** » Sat Oct 06, 2012 6:54 am

Regardless of whether it was intentional or not, I am always fascinated that there appears to be different directional vectors in the line. In this one we have line going forward and down in the same cast. I remember seeing a similar effect in Aitors cast:

http://vimeo.com/25940661

The only way I can see these being achieved is by having a null in the line tension at a point in the cast that is not recovered.

gordonjudd · Post by **gordonjudd** » Sat Oct 06, 2012 7:03 pm

Photo of funny looking loop cut from this video:
Alexandar,

Thanks for taking the time to make your video. I think a video is worth a 1000 pictures in this case since it shows the sequence of events in real time.

James intuition was right on. The bend down in the rod that bothered me was from a second counterflex motion of the tip of the rod as it recovered from bending up while it was pulling down on the rod leg after the loop was formed.

The only way I can see these being achieved is by having a null in the line tension at a point in the cast that is not recovered.

Vince,
What do you mean by "a point in the cast that is not recovered"?

I don't think you need to have zero or near zero tension except right at the fly end of the line. The line is a flexible distributed mass and just tends to follow the direction the segment that is just ahead of it is pulling on it. It always takes a force (tension in this case) to change the direction a mass is traveling, but since the line is flexible that force can be pointed in different directions at different points in the line.

Gordy

James9118 · Post by **James9118** » Sat Oct 06, 2012 7:58 pm

I've been out casting this shape today - took some photo's but don't feel they're good enough to post due to the background (the shape is correct though, albeit with a slightly wider loop - see below). I'm casting in a field tomorrow (BFCC) so I'll have another go.

The faster the downward mend is made, obviously the more vertical the 'dog-leg' is. Also, the faster the mend the more counterflex occurs at the bottom. I was using a long belly WF which I think tended to pull the loop open a bit, I believe using a short bellied WF line and performing the mend on the released running line would give you the exact shape.

VGB · Post by **VGB** » Sat Oct 06, 2012 11:00 pm

Gordy

If tension was constantly applied I would agree with you. The low tension areas can form if tension is applied, released and then a lower tension is applied. It is problematic for the hose in flight refuelling systems (UK) and towed arrays. The 2nd counterflex is releasing and reapplying low tension. If it was higher tension the line would be pulled straight and the right angle would not form

gordonjudd · Post by **gordonjudd** » Sun Oct 07, 2012 3:38 pm

The 2nd counterflex is releasing and reapplying low tension.

The tension may be smaller but it is not "released" or going to zero. The tip is still causing the direction of the line's momentum to change. That requires a force and in this case that force component comes from the tension applied to the line.

It is very rare that you see a "kink" in the rod leg portion of the line as the tip is going through counterflex to indicate a region of zero tension. More likely that counterflex motion is going to generate a transverse after bounce wave going down the line. To get wave propagation there must be some tension in the line, so I do not think;

The only way I can see these being achieved is by having a null in the line tension at a point in the cast that is not recovered.

is true although I still do not understand what "a point in the cast that is not recovered" might mean.

If it was higher tension the line would be pulled straight and the right angle would not form

In a static situation that might be true, but by an large we are dealing with wave motion in a flexible medium.

That wave motion requires tension in order to maintain the propagation of the wave. Thus there is always tension in the line going around the curved portion of the loop. Without tension the line turns into spaghetti as you can see at the end of Alexander's cast

Gordy

VGB · Post by **VGB** » Sun Oct 07, 2012 4:40 pm

Gordy

I did not say that there was no tension in the line, only a null at a point in the line. I understand your description of stress tensors. If you measured the tension between 2 points an inch either side of the point of the right angle what would it be?

Try taking a shoelace, hold it in tension and form a right angle with it whilst maintaing constant tension and staying in the same plane.

blackwater · Post by **blackwater** » Mon Oct 08, 2012 3:20 pm

This looks like the loop shape from the original picture. As Stu said in his response the cast is just made like normal and then the rod tip is pulled towards the ground. The amount of time you wait determines the length of loop in front of the step.

gordonjudd · Post by **gordonjudd** » Mon Oct 08, 2012 3:20 pm

If you measured the tension between 2 points an inch either side of the point of the right angle what would it be?

Vince,
Nominally the same since Hendry states the tension in the bottom leg of the loop is nearly constant.

Try taking a shoelace, hold it in tension and form a right angle with it whilst maintaning constant tension and staying in the same plane.

As I said that is a static example of the effects of tension in a string. As Mike Hendry explained in his thesis we are dealing with the tension that is related to the propagation velocity of a wave in a string.

As you might expect, the difference between those two cases is much different.

Gordy

gordonjudd · Post by **gordonjudd** » Mon Oct 08, 2012 3:31 pm

This looks like the loop shape from the original picture.

Another great example of how that loop shape is formed.

Was that picture taken at night under lights to get such a black background? I am surprised you could use the fast shutter speed required to to "freeze" the line under those low light conditions.

Are you able to take videos with that lighting? As you know it is not easy to find a place where the sun is behind the caster so the line is well lit and still have a black background. I am still looking for a place with those conditions as I can never find a place where the line will stand out taking high speed videos with shutter speeds of .001 seconds or less.

Gordy

blackwater · Post by **blackwater** » Mon Oct 08, 2012 4:00 pm

Gordy, that is a screen shot from a video. It was taken under lights at the Northern Suburbs Casting Club in Melbourne.

The lights are fantastic but when trying to video in slo-mo at more than 120fps i get a very strong strobe effect.

Hopefully this link works. I have no idea how to link any other way from youtube onto here.
Weird loop shape

alp · Post by **alp** » Mon Oct 08, 2012 5:02 pm

gordonjudd wrote: As you know it is not easy to find a place where the sun is behind the caster so the line is well lit and still have a black background. I am still looking for a place with those conditions as I can never find a place where the line will stand out taking high speed videos with shutter speeds of .001 seconds or less.

Gordy, if you do not have artificial light and you want to improvise, it’s very hard to find a dark background with the sun directly behind you. Even a flat full black surface will not look black on your photo.

The sun must be in front of you and slightly to the side. So you'll be able to find a full shadow in front of you that will look completely black. It may be part of forest or some rocks, for example. Color of background is irrelevant because shadow will look black.

Then put something that will make a shadow over your camera. Up and slightly to the side of the sun. You may take a newspaper or anything like that. Measure the light pinpoint on the caster. If you do it well, line will shine, you will see every drop of water in the air with the black shadow as a background.

With a simple pocket camera line can look like this. With good equipment it will look perfect.

gordonjudd · Post by **gordonjudd** » Mon Oct 08, 2012 7:36 pm

The sun must be in front of you and slightly to the side.

Alexander,
That looks terrific.

I like to have the camera positioned at right angles to the direction the loop is traveling to eliminate as much as possible the perspective distortions that arise when the loop is closer or further from the camera.

If the camera was positioned more to the left to get a better perspective will that spot still have strong shadows in the background?

Gordy

alp · Post by **alp** » Mon Oct 08, 2012 9:41 pm

Gordy, you can improvise as long as the sun is in front of you, more (or less) to the side. When this relationship changes the effect of shineing rod, line and water drops on dark background disappears.

By the way, this way of shooting you can find in many books. The Essence of Flycasting, The Cast… Try to analyze these pictures, structure of the background, the shooting angle, direction of light and shadows.

Use a fast shutter speed and do not forget to put a shadow over the camera. Another good tip is to use tele lens for such things because they will blur the background.

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