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Instant Center of Rotation Flow - How does the I.C. move during a cast?

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Paul Arden
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Post by Paul Arden »

About seven years ago, a friend of mine and I studied clips of Hartman, Rajeff, Walker and the others in the "Big Hitters" section. One of the interesting conclusions we came to was that distance casting required "late rotation". It would be fascinating to have had the ability to shoot in High Speed and watch the IC relate to each Casting Stroke. I have to get a high speed video camera. The database of casters I could collect would be staggering.

Great to watch the difference between your stroke and Chris' accuracy cast, Gordy. Fantastic stuff.

Cheers, Paul
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Merlin
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Post by Merlin »

Paul

My new numerical model fitted with a variable function of rod stiffness with line/rod angle and deflection does show that the "late rotation", in the sense you are meaning, does show a significant advantage in terms of line speed.

Merlin
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Post by gordonjudd »

Great to watch the difference between your stroke and Chris' accuracy cast, Gordy. Fantastic stuff.


Paul,

And I wish my accuracy stroke looked more like his. He learned to use the big muscles in his shoulder to cast when he was a kid so he could practice with Steve Rajeff for 6 hours a day. Consequently he developed a very efficient casting style that he can do for hours on end.

You will note he has a very restful position of his elbow at the end of his stroke while waiting for the loop to roll out to the target.

Image

Contrast that position with mine as I am waiting for the line to roll out (a position you are in for a relatively long time when false casting). It takes more effort than you might think to hold the rod that far away from the body.

Image

When Chris does a clinic he has people hold the rod where they end up at the end of their cast (like mine above) for a couple of minutes, and most people find they can't last that long.

Get the elbow below the shoulder like Chris does, and holding that position for a long time is a piece of cake.

Those are the subtle things good tournament casters do so they can make repeated false casts in the dry fly game when it is windy (and it is almost always windy at the Golden Gate casting ponds), without getting tired.

Gordy
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Paul Arden
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Post by Paul Arden »

Merlin wrote:My new numerical model fitted with a variable function of rod stiffness with line/rod angle and deflection does show that the "late rotation", in the sense you are meaning, does show a significant advantage in terms of line speed.
Hi Merlin, this is very interesting indeed.

Gordy, It would be great to see Chris' distance cast viewed in the same way!

Cheers, Paul
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Post by gordonjudd »

Gordy, It would be great to see Chris' distance cast viewed in the same way!


Paul,

As you might expect his hand path and instantaneous center of rotation (I.C.) flow is much different in a distance cast (in this case using a shooting head set-up) as shown here.

The butt angle and angular velocity plot for that cast is shown below:

Image

You can see he rotates the tip of the rod down as he starts forward by about 10 degrees during the first .3 seconds of this cast. While the angular velocity is negative the I.C. is above his hand. When he starts the forward rotation of the rod the I.C. flips so it is below his hand at about the -.3s time point in the time counter on the video.

I am not sure how Vimeo does the time scaling on the timer in the video. The high speed video contained 255 frames. At 300 fps the real time of that clip was .85 sec long. Vimeo's time counter at the end of the clip was 17 seconds. So it appears that the time counter on Vimeo is 20 times the real time value. I added a time counter on the video that should match up with the time scale on the plot.

Gordy
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Post by John Waters »

Hi Gordon,

Great overlays and videos and illustrates that the more vertical the elbow movement coupled with late rotation and block using the heel of the hand allows the fly to hover over the target. That wrist and upper arm block (locking the elbow) allows the caster to better sight the fly over the target on water. It can also set up a power ripple down the line but for target casting that is not an issue (refer Chris's fly accuracy record). Steve can cast with the same blocking actions and not get a power ripple but that is Steve's great casting skill. However, given the above, observing the video of Chris from behind surprises me a tad. Do you recall if he was casting to a Dry Fly, Skish, Trout Fly or was it a Bass Bug event?

John
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Post by gordonjudd »

A video that shows the I.C. flow for Mathias' 10 meter cast using a Paradigm rod can be viewed here

This is interesting because the perspective is far enough away that the I.C. stays in the frame of the video throughout the cast. The I.C. moves to a point near his elbow near the maximum angular velocity point of the cast, and then moves away from him as he stops the rotation of the rod while continuing to translate his hand.

His hand path is much more horizontal than the up to down path that Chris Korich uses in his tournament casting stroke, and as a result is hand is extended from the body at the end of the cast.

A plot of the butt phase angle and angular velocity for this cast is shown below:
Image

Many thanks to Grunde for sharing his high speed video data.

Gordy
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Post by Bobinmich »

Wow! This is really cool stuff!

Now if we could get a high speed camera in Paul's hands and have him film a shit pot of casters and give them to Gordy, we could finally put this rotation/translation thing to rest. When we switched over to looking at I.C., motion is just motion and it is all rotation around the instant center at that particular instant. We could even look at line speed and find where maximum energy transfer is occuring. I'm starting to get interested again. Damn, I was trying to avoid that.

BTW I can't believe that I was only a few inches off from the Paradigm rod cast when I picked a I.C. for that pie chart I made a few years ago. Talk about lucky.

KUTGW guys!

Godspeed,

Bob
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Post by Paul Arden »

I remember asking this before but I've forgotten the answer. Which High Speed camera should I buy? Many thanks, Paul
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Post by gordonjudd »

However, given the above, observing the video of Chris from behind surprises me a tad.


John,

What is it that surprised you by looking at Chris' casting stroke from behind?

He was demonstrating his basic accuracy casting stroke when that video was being taken, and I think he would claim that he uses the same accuracy casting stroke regardless of the game involved.

However the long shot to the last target in bass bug and the pick up and laydown used in the Western rules wet fly game would likely be exceptions to that "same stroke" assumption. Since he was just false casting here, it would likely be the closest to the stroke you would see while making distance adjustments in the dry fly game.

Gordy
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Post by gordonjudd »

I remember asking this before but I've forgotten the answer. Which High Speed camera should I buy?

Paul,

It would depend on your budget of course, but for the money I think the Casio EX-F1 and EX_FH25 would be hard to beat.

There is a used EX-F1 for sale on E-bay that might be a great deal if you could manage to win the auction.

Gordy
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Post by gordonjudd »

BTW I can't believe that I was only a few inches off from the Paradigm rod cast when I picked a I.C. for that pie chart I made a few years ago. Talk about lucky.


Bob,
I am not sure when that few inches was being measured, but if I understand how you computed the I.C. as being the fixed intersection of where the butt is pointing at the start and end of the cast as shown here
Image

Since the I.C. is changing throughout the cast and is not at a fixed point was your "few inches" estimate arrived at MRF as shown here?

Image

I think you would agree it is more than a few inches early in the cast as shown here
Image

or near RSP as shown here:
Image

The distance from the hand to the I.C. varies considerably during that (or any) cast, so I don't think you can pick a fixed point for it that has much relevance to what is actually going on.

That is the conclusion that I expect most people would take away from looking at the different casting examples.

Gordy
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Post by Bobinmich »

"The distance from the hand to the I.C. varies considerably during that (or any) cast, so I don't think you can pick a fixed point for it that has much relevance to what is actually going on.

That is the conclusion that I expect most people would take away from looking at the different casting examples."

I agree completely.

The I.C. I happen to choose for that calculation was 1 foot below the rod handle and in line with it. Since I was using an instant center, the calculation would have meaning for that instant only. The only purpose of that calculation was to show that relative contribution of the various rod/reel/line parts to the felt load at the handle. The I.C you show in the position I did the calculation is about at the elbow. Depending on how you hold your rod, for me this was probably close. Considering no one was even thinking I.C. at that time (2-3 years ago), it was, as I said, probably close enough for government work. And when you start thinking I.C., translation/rotation become just motion.

Why do you have to be so picky all the time Gordy? I have the utmost respect for you and your work. You need to try to show others the same courtesy.

Bob
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Post by John Waters »

Hi Gordy,

Thanks for your reply to my question re what event Chris was casting. The first thing I looked at when I saw your video of Chris casting from the rear was the loop shape and I thought the line would hang a bit longer in the air. However now that you have explained that it was a demonstration of the stroke that explains the loop behaviour. They can be two different outcomes. When trying to judge a dry fly target length the loop profile and trajectory and therefore the fly behaviour, is critical and epitomised by the rod butt block exhibited by casters of the ilk of Steve Rajeff and Chris Korich. Ditto in the vid of Steve casting in the Fishing Gear Event this year. Leaders have a part to play and even choosing a lighter line (conditions dependent) also helps, but the technique is primary.
You are correct with the Wet Fly (particularly the top two targets) and the Bass Bug, hence my question.
Thanks again for your response, am learning heaps.

John
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Post by John Waters »

Hi Paul,

A friend recommended a Casio EX FH100 to me last year and I was not disappointed.

John
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