IV The Acceleration Phase - the meat of the cast…and the model.
In Bob Bolton’s diagram (Fig. 1) the acceleration phase is shown as being, diagrammatically, quite long. That is certainly NOT a time line. More appropriately, the x axis would be “importance to the cast“. Things are happening quite fast from here on. It is all over in a fraction of a second. It takes high speed cameras to see what is going on…or a simplified model.
There is general agreement, based on at least some investigation, that the final phase, UNLOADING, contributes no more than 11-18% to the totality of the cast. It is not clear whether that percentage is line speed or energy, but the point remains that the vast majority of the line acceleration is accounted for in the first two phases…and the vast bulk of that in this split second Acceleration phase. An 8 wt head (220 grains) is the same weight as a common .30 caliber bullet. A little gunpowder does a very dramatic job very quickly.
Given it’s huge importance to the cast, interestingly and fortuitously, this Acceleration Phase is modeled as being a very simple system.
Bolton, and every other investigator has modeled and in some cases physically proven that in both the ideal modeled cast and in actuality in the hands of expert casters, this is best described as a phase of constant acceleration.
The implications of that simplicity, the fact that up to 85% of the energy or distance of the cast occurs in a simple, stable state has, in my opinion, been under-appreciated and under-exploited in terms of describing the instrument that lies between, in the simple F = Mass x Acceleration equation, the Force and the Mass.
Force = Mass x Acceleration. IF acceleration is constant (and we accept and can prove in expert hands it is) and since the Mass at this point is given and constant, then the undeniable conclusion is that all the forces on the fly rod have stabilized and that for the entire (short but important) time that acceleration remains constant that the shape of the rod is nearly static and unchanging.
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