[WS] With respect to rod loading we did have some discussion in this group and the consensus was that “loading” is not a great term and that bending and straightening were better terms to describe what happens with the rod during the cast. I think that saying that a loaded rod is a bent rod is still acceptable.
[DlB]A rod bends because it is loaded by forces: e.g. torque from caster, inertial forces (line, rod weight) and drag (air).Both are linked so it is not a question of “acceptability” but of what you are looking at. Bend speaks to all, load speaks to specialists.
[WS] I like that. In the past I’ve talked about load being a mechanical engineering term that actually makes good sense in this context but most people are not mechanical engineers and are not familiar with this term or its use in this context. Bend is a term everyone understands.
The issue is that saying that a rod is loaded creates the impression that the purpose of the casting stroke is to load potential energy into the rod which can then be released at will to throw the line similar to loading a gun or a catapult. This has a few issues. To begin with the energy for the cast comes from the caster. During the casting stroke some energy is stored in the rod and it is recovered when the rod straightens at the end of the casting stroke but this straightening does not increase the amount of energy that the caster puts into the stroke.
[DlB] But to get that stored energy, the caster had to produce it anyway, of course there is no external generation of energy apart from the caster, then it takes various forms: kinetic (rod, line), elastic (bended/loaded rod), losses (air drag).That stored energy goes back mainly into the line at the end (RSP, some is lost through air drag.
[WS] With a gun the energy generated by the bullet is much greater than the amount of force the shooter exerts on the trigger. If we look at European style distance casting there is little or no recovery of the energy that is stored in the rod by bending it.
[DlB] I cannot see a technical reason for that lack of recovery. How would you explain it? Because of the angle between the rod and the line at the end? For me it goes into the line, or should I say into the fly leg and also into the loop for a 170 style.
[WS] I know we’ve had this discussion before and I don’t think we will come to complete agreement on it. Given that force is a vector quantity we need to apply force in the direction that we want an object to move in order to make it accelerate and move in that direction. If we apply force in any other direction than we intend the object to move in then the object will not move in the direction we want it to move but it will move in the direction we apply force. That should be obvious when we are talking about point masses but the line is a long flexible object so we have to consider that even though we may be pulling the line at right angles to the direction (let’s call this the X direction) we want it to go the line will not move as a point mass in the direction we are applying force, the end we are pulling on will move in that direction but the line following this will form a curve resulting in forces in the Y direction along the curve as well. If we look at rod straightening in a non-170 cast, i.e. we stop the rod so that the rod tip straightens in the direction of the cast, it’s easy to see that whatever potential energy there is in the rod is going to contribute to line speed in the direction of the cast. In the 170 cast the rod does not unload or straighten in the direction of the cast. It unloads at nearly a right angle to the direction of the cast. Only a portion of the kinetic energy that is generated as the rod straightens goes into the fly leg, much of it actually goes into the rod leg and results in the large loops we typically see in the 170 cast. I will attach a picture to make this clearer (I hope).
Another issue is that we can’t do much to prevent the rod from straightening once it has reached its maximum bend. We can perhaps delay the straightening by a few hundredths of a second but short of hitting a solid object with the rod it is going to straighten no matter what we do. One of the main benefits of rod bending and straightening is that it contributes to our ability to maintain a straight line path of the rod tip during the casting stroke. Using the term loading doesn’t really describe this.
[DlB] Above the contribution to a longer and straighter tip path, rod bending allows the caster to put a greater part of the energy he produces into the line. This is why the “flexible lever” is better than the “broomstick” for casting.
[WS] Agreed, but this is really the advanced stuff we are talking about now. Briefly, you are talking about how the spring effect allows us to apply more force to the line over the casting stroke than we would be able to with a “broomstick” or a rigid lever.
I’m comfortable with bending or loading, but maybe bending is more practical for instruction since anyone can see it.
Thanks Daniel! This is a very interesting discussion.
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