vincent p. norris wrote:
Physics of fishing
at http://www.washtimes.com/metro/20050...0210-5222r.htm


" Ideally, the energy directs the fly to the target, he says. The
most efficient way to accomplish that goal is through a straight line
path of the rod tip.

"If the rod tip doesn't travel in a straight line path during the
cast, it either becomes convex or concave. A convex path of the rod
tip creates a wide, inefficient loop."

The rod tip becomes convex or concave? Wow!

Aside from that second paragraph's being an example of damn poor
writing (not extraordinary for the DC Times), the whole quotation is
nonsense.

I'll wager that there is no one in the entire world whose rod tip
describes a straight line when he or she casts.

Assuming the rod maintains a constant length during the cast, which is
the case with most rods I've seen, the tip follows an arc, not a
straight line.

vince

Indeed it is a badly written mish-mash of an explanation. However in the
casting stroke, backwards or forwards, the rod bends due to the mass of
the rod and the mass of the fly line attached to it being accelerated.
So the path of the tip is not a simple circular arc, but at a minimum
will be flattened towards straight from such an arc due to that bend in
the rod. All the well-known casting gurus, Lefty Kreh, Joan Wulff, Mel
Krieger will tell you that the optimum rod tip path is a straight line,
and there is plenty of video to back them up. If the cast is
overpowered, the path will be concave and usually results in a tailing
loop. If you try to cast a line that's too light for the rod you won't
bend the rod enough, and get the convex path. If the line is to heavy,
it will bend the rod too much during the stroke resulting in the concave
path. Within limits though, these effects can be controlled with technique.

But the worst thing about the article is that it dances around but
doesn't really get at the essential physics of what makes a fly cast
work. What it is, is that at the instant the loop is formed, the whole
line is in motion and has a certain amount of kinetic enery. As the line
rolls out, the energy that was in the part that goes static transfers to
the moving part. In the absence of air resistance the speed of the
moving part would continually increase due to this effect. It would
theoretically go infinite just as the end of the line is reached.
However among other things, the tensile strength of the line would be
exceeded, and it would break before this happened. With air resistance
there is a balance between the loss due to it and the transfer of energy
from the static part, and the line unrolls at more-or-less constant
speed. Narrow loops are preferred because less frontal area has less air
resistance.

Mike