I've been thinking about how I could better illustrate and explain that wrist flick or power snap to you. It is the final acceleration of the fly rod. To be more precise, it is the the rapid rotation
of the fly rod butt and the rod tip just before the stop. By flicking the wrist to a hard stop, you rotate the rod butt, which moves the rod tip through an arc.
There is a way to show this on a graph and to demonstrate two different rates of rod butt rotation or power snap. Some of you are familiar with the Casting Analyzer.
Explanation of the casting analyzer graph is below. The power snap is the final acceleration phase of the graph below.
Jason's Borger has posted the difference between a standard overhead cast and a roll cast in terms of rod "butt" rotation. Read the comment between Jason and I below the article:
Graph from Jason's Blog, the top graph is the standard cast and the bottom is the roll cast.:
The difference between the two graphs is that the final (acceleration) rod loading for a roll cast (lower graph) must occur over a shorter time and have a higher peak. It requires more energy to make a roll cast because part of the energy is used to both elevate the line and to break the line free of surface tension.
The standard casting instruction for the roll cast has been that it is just the same as the a regular forward cast. We can see that that is not quite correct. If you look at the white side of the graph, the initial front part of the curve (from about 37 to 55 ms) is identical UNTIL the final
steep acceleration from 55 to 58 ms. So the final application of power is more sudden and forceful than an in the air cast
The other thing to notice is that even though the final acceleration is more sudden and rapid, it is still SMOOTH. There are no dips in the acceleration line.
So a roll cast requires a faster rod rotation over a shorter time.
It requires a harder power snap.
This is what I meant when I said that your casting stroke lacked "oomph".