fly rod deflection and rotation

Looking through fly fishing forums I often read a statement like this: „we rotate the fly rod and as the inevitable consequence it deflects“ (and again recently “rod bend is a consequence of our main purpose to rotate the rod”).

This statement left me unsatisfied. On the one hand I totally agree that the rotation of the fly rod is vital to generate a proper line speed to get the fly into the target. But on the other hand I was missing something. To me this statement felt uncomplete somehow, since in this view the meaning of the deflection tends to be a kind of byproduct of the rotation reduced to some geometrical advantages – basically to carry the tip of the fly rod on a straight path.

Since my „Experimental investigations on the fly rod deflection“ I can explain what I was missing: the meaning the deflection could have in terms of efficiency (ratio of output / input energy) !

As one conclusion of my investigations there is no doubt that the deflection of the fly rod enables a significant better energy transfer from the grip towards the tip. In comparison to a totally rigid fly rod – which provides basically leverage resulting from the translatory and the rotary motion – the flexible one provides two further transfer properties: 1.) the storage of energy (spring energy, the „load“) as well as 2.) the redistribution of angular momentum (associated with the modification of the moment of inertia – see section F1 and annex 2 of my investigations). Both further energy transfer properties interrelate and enable the caster to generate a proper line speed with less effort, if he deflects the fly rod in a proper manner ! Even if the rigid as well as the flexible fly rod could be massless – as investigated in my work – the flexible one has a significant better ability in energy transfer than the rigid one.

What is the insight ? The rotation in combination with the controlled deflection as well as the controlled counter deflection (reduced counterflex) is the key of an efficient fly cast ! In terms of efficiency a closer look on HOW the fly rod is deflected is important instead of THAT it just deflects as a consequence of rotation. The rotation is vital to achive this and it is always effective (“the aim is all”) somehow – but without a proper deflection the rotation alone is not efficient (1).

I produced some videos with should clarify what I’m talking about.

read on scribd

(1) Scientists would say, that for efficiency the rotation is a necessary, but sololy not a sufficient condition ! Both conditions are only met if the optimal deflection joins the casting stroke !