Concave-Convex / Overhang. Influence on loop size

Walter & Group...

David Leger and I have had a discussion about the terms "CONCAVE" & "CONVEX" as so often applied to the path of the rod tip when fly casting.  These terms are sometimes confused by candidates taking both CCI and MCI tests.  I think that is most often due to the fact that they sound a lot alike.  There may be some, however, who look at these terms differently.

David has correctly pointed out that these terms are only relative to a frame of reference.  Here is my answer to him .... G :-

David,

Got your last message and could read it, but for some reason there was a "script error" which locked up my computer.  I finally got it unlocked via the task manager, but couldn't reply to it directly.  (I can't figure why that happened.)  For that reason, I couldn't copy it.

 

You are right about having a frame of reference.

 

 

Here is what I found in my Webster's Dictionary:

 

CONCAVE:

 

1. CURVED LIKE A SEGMENT OF THE INTERIOR OF A CIRCLE OR HOLLOW SPHERE.

 

2. Geom.. (OF A POLYGON) HAVING AT LEAST ONE INTERIOR ANGLE GREATER THAN 180 DEGREES.

 

3. Obs.  HOLLOW.

 

4. mach. A CONCAVE PIECE, AS ONE AGAINST WHICH A DRUM ROTATES.

 

 

CONCAVE:

 

1. HAVING A SURFACE WHICH IS CURVED OR ROUNDED OUTWARD.

 

2. math. (OF A POLYGON) HAVING INTERIOR ANGLES LESS THAN OR EQUAL TO 180 DEGREES.

 

 

The bowl is a good analogy.

 

In fly casting talk, the way we use the word CONVEX with respect to the rod tip path, it is the outside of the bowl turned upside down.  We might look at this tip path as rising, then descending.

 

CONCAVE, would be the outside of the bowl with the bowl turned right side up.  One might choose to describe this rod tip path as dipping downward (descending) and then rising upward.

 

Reason is that in fly casting, we customarily refer to the rod tip path in relation to the ground / water while making the assumption that a vertical casting plane is being used.  Those assumptions can sometimes get us into trouble as we try to describe things.  One example is the common way of looking at a fly line loop as having an "upper leg" and a "lower leg".  This is the reason I prefer to use the terms "fly leg" and "rod leg". (There can be no "upper leg" or "lower leg" when we cast in the horizontal plane.)  When used in this manner, then:

 

CONVEX:    Examples would be the rainbow or an outline of an exkimo's igloo.  A path which rises, then decends.  A dome.  Shape of a mountain.  Path of the rod tip which rises, then falls.  A "U" turned upside down.

CONCAVE:  Shape of saucer.  A path which decends, then rises.  A dome turned upside down.  Shape of a hole in the ground.  Path of a rod tip which dips down, then rises.  Shape of a "U".

These are based on the ground or water as the frame of reference.

 

If we have no frame of reference, then a curved line may be seen as concave and convex at the same time !

 

Casting in the horizontal plane, we don't have that frame of reference.  In this instance we might say that a convex rod tip path is one which travels to the casting hand side, then to the line hand side.  A concave rod tip path would then be one which travels first to the line hand side and then to the rod hand side. Of course, that goes out the window if we are casting back handed !!!

 

If we look at this bowl with no reference to the ground; rather a reference to an imaginary plane at the edge of the bowl.... say floating out in space, then I'd say that the inside of the bowl is CONCAVE, while the outside is CONVEX.  Or (more accurately) that this bowl shape is CONVEX if its rim is against an imaginary plane.  It is CONCAVE if the bottom of the bowl is against this plane.

 

In the end, I favor sticking to the way these terms have been used by fly casters because almost all instructors and fly casting authors have been using them this way.

 

If you wish to blow your mind over this stuff, try what I did.   .....  I stood on my balcony, 15' above the ground, leaned over the safety rail, and made different casts with the rod hanging vertically straight down.  Vertical casting plane, to be sure ...... results were interesting. Firstly, the "top leg" of the loop becomes the "bottom leg".  (Subject for another time. )

 

 

Gordy

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                                                               Overhang affecting Loop Size

 

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Jim Penrod poses this question on the relationship between overhang and loop size :-

 

Hi Gordy,

   One of the recent posts discussed shooting heads, overhang, etc. I can understand how some overhang leads to a longer cast (the longer time it has to unroll the longer the cast) and why having no overhang prevents such with added friction, less mass out of the rod tip. However, I am having trouble brain wise in figuring how overhang effects loop size. With too much overhang I cannot get enough energy down the line to move the line well and a lot of that energy is taken up when the mass changes and I think that leads to a larger loop. But how does it relate to a smaller loop?

Jim

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Jim .....   Let's first look at a few things which have actually been observed.

 

1.)  Even the best casters cannot shoot much more than 50 % of the fly line carried while false casting. This is due to a number of factors only one of which is friction between the line and the guides and tip top.  (This is an approximate figure and will vary with the caster, the tackle, and the wind.)

 

2.)  Carrying increased shooting line has resulted in longer casts.  The reasons, we've gone over in recent messages.

 

3.)  When the caster tries to carry more line while false casting than he/she can handle well, distance suffers despite 2.), and the loops become wider.

 

As I see it, whether the loops can be maintained small is strictly a matter of CONTROL.  The evidence that this is true:

 

Expert (elite) distance casters routinely carry lots of shooting line (overhang).  This helps them achieve greater distances. As they do this, they maintain excellent control with reasonably straight line paths of their rod tips in all planes. THEIR LOOPS ARE SMALL.

 

As I coach Master candidates who are having trouble with their distance casts, I see as the most frequent error, that they try to carry more shooting line (overhang) than they can handle well.  When that happens, this lack of control results in the loops opening up as they start to lose what often started out as almost straight line rod tip paths.  Most often, this is in the form of mal tracking, so it is more apparent as I watch their loops from in front or behind since this is a side-to-side deformation of the rod tip path.

 

 

SHORT ANSWER:  Overhang does not directly determine the size of the loop.

 

 

Gordy

 

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Sam Doyle asked me to re send him our Group message of December 6, 08.  This one had a ground casting diagram and a thumbnail guide with attachments.  I couldn't retrieve it because that was during an interval when my computer crashed and I lost some data.

 

If any of you can dig this up, please forward it to him at:  sdoylekpsp@xxxxxxxxxxx

 

Thanks !

 

Gordy

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