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[GH] I'm back from Spokane. Arrived here in the Florida Keys in time to witness the hazy yellow skies resulting from sand storms in Africa. Our flats fish don't seem to like this. Happens almost every year at about this time. It is predicted to be worse next week.
Now we're getting into comments on the various answers we received. This is valuable, because it really makes us think. It also adds a few brain teasers.
As we play with these things mentally as well as out in the field casting, we can get a bit confused. Eventually, however, we can end up with a better in-depth understanding of what is going on as we cast.
Gordy
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>From Guy Manning:
Gordy,
RE: The answer that I got came from Troy Miller and it is worth repeating.
''When something translates in scientific terms, it simply moves through 3-D space from point A to point B. While it's doing this, it may be rotating, it may be changing color, it may be laughing, it may be getting smaller. .. But it is moving through 3-D space. As in, its center of gravity has changed position. Many people think that translation implies linear movement, but it doesn't. You could move from A to B in an infinite number of paths, but there's only ONE linear path. In the grand scheme, that's the one that I'm trying to make my thumbnail (and the rod tip) imitate.''
According to every definition I have ever looked up (at least 3) and according to the ones you offered, translation excludes any rotation. All parts of an object cannot remain parallel to the other if the object is rotated in the slightest way. So the above statement can't be true unless you remove the phrase about rotation.
Re: Mark Surtees comments.
"If casting angle refers only to the angular change in position of the rod, then the only way to practically do this during a casting stroke is to use the wrist and permit no other movement of hand, arm or body. This cannot be how such a thing is done mainly because its barely physically possible, except perhaps at exceedingly short line lengths. Casters use predominantly hand path coupled with angle change to deal with the changing bend profile as it displaces up and down the rod just because it’s, physically, way easier.
Almost any casting video will demonstrate this so its puzzling to find any resistance to the idea when it’s evident in every cast we see. There must be a reason for this and so it is quite attractive to believe that when people refer to casting arc or angle in this particular context they are referring, not to a single term of angular measurement, but to the whole movement of the rod created by combining the rotation and translation that we use to achieve some change in value of that term. In which case we are talking about something different to just Casting Angle, the angle."
I'm not buying this. If we are going to be strangled by the engineers every time we misuse a word then Mark has a short life expectancy :)
If I use this \/ then add stroke length and get this \ / the angle hasn't changed. Yes the rod the rod tip and butt have travelled a greater distance, but if you put a protractor on both, the result is the same casting arc, angle or whatever you want to call it. Unless we are casting solely from the wrist, with the use of no other joint (elbow, shoulder, spine, legs), then we are adding stroke length via translation. Stroke length and casting arc are two entirely different animals and should be defined as separate to a student. Maybe what Mark is trying to get to is the fact that a lot of people don't separate the two. I have had prospective CIs surprised to learn this.
I do agree that one can use the same stroke and arc to cast various lengths of line by increasing force. A few years back someone stated this was possible on SL, in context of a larger discussion, and was ridiculed. I responded that it was indeed possible and was greeted by silence on the matter. It isn't something a person will spend a lot of time at, as Mark states. It takes a lot of physical energy to accomplish. It is easier and much more comfortable to use a longer stoke and less force.
Guy Manning
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[GH] Guy,
My "working definition" of translation may not be scientifically pure, but it works for me as I apply it to fly casting :-
Translation: "Straight line movement between two points."
Now let's try to apply that to Troy Miller's comments. An object can go from point A to point B in a straight line path even if that object is spinning, twisting, turning, shrinking or expanding. Translation, then is the PATH taken. Troy takes the position that that path need not be linear (straight).
However, let's look at the definition in Webster's Unabridged Dictionary:
"Translation. mech.: Motion in which all parts of a body move with the same velocity along parallel paths."
As I try to interpret this, it seems that movement with all parts traveling in parallel paths with the same velocity would allow that motion to be straight or curved !
Perhaps I'd be more scientifically correct if I used terms like, "linear movement" or "translation without rotation".
Other definitions: http://en.wikipedia.org/wiki/Translation_(geometry)
Re: your comments on Mark Surtees' message -
1. During our deliberations on the FFF BOG Glossary Committee, we did agree to call the Casting Arc, "The angular change in the position of the rod butt during the casting stroke." As you know, our definitions were not formally approved by the BOG.
The SexyLoops definition: "Casting Arc: Change of rod-angle during a Casting Stroke."
2. I think Mark was trying to emphasize the point that while Casting Arc and Casting Stroke are two different things (as you point out) they usually occur simultaneously as we cast.
3. Years ago, Mel Krieger drew the Casting arc the way you did: \/. When translation was added, he came up with the figures: \ / all the way to: \ / and called that, "The variable casting arc".
We could call : \/ our Casting arc. We could also call: \ / our Casting arc as part of (within) our Casting Stroke.. If we were adding some initial almost pure translation which some call, "drag", casting to the left of the page, we'd have: \ / /. Argument as to whether "drag" should be within or without the casting stroke would still persist.
If we eliminated "drag" and, instead added CREEP, It might look like this: \ |/. (CREEP being very slow rotation mixed with just a bit of translation which many see as shortening the effective Casting arc and Casting stroke.)
4. If I take the same rod and make two casts.... one with a good match between casting arc and rod bend for rod tip SLP .....and the second with the same casting arc and greater rod bend due to greater application of force, I daresay I'll have a concave rod tip path leading to a tail.
HOWEVER :
If I make that second cast with a much stiffer rod, then I MUST use increased force with the same casting arc to achieve a straight line path of that rod tip because that extra force is needed to make that stiffer rod bend enough to match the casting arc for a rod tip SLP! (That's what strong super casters like Steve Rajeff do for their competition distance casts.)
5. In March, I gave a casting lesson to a chap who had a plaster cast on his wrist. Despite the "locked wrist", he was making big wide loops with a convex rod tip path by the compound movements of his elbow and shoulder yielding lots of rotation. Didn't need the wrist to do that.
6. For demonstrations, I have made up a "fly rod" out of a broom stick... tip ring, guides, etc. It won't bend. With this, I can make short casts with true albeit large loops.
So many variables. As Dennis Grant says, "IT DEPENDS" !
Gordy
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