A taper is what defines a rod's action. Action is how the rod flexes during casting. By modifying the diameter of a rod throughout its length,
one can make rods with massively varying degrees of actions.
Tapers are designed in many ways. Trial and error are always
the final factors in determining whether a rod is 'good' or not, but there are
other ways of creating and modifying tapers.
Everett Garrison, being an engineer, created a way to look at bamboo rod tapers
by graphing the stress at each point along a rod's length. The stress values of a rod are
computed by taking many variables into account including the weight of the
bamboo, finish, guides, ferrules, etc. plus the diameter of the rod along points
along its length. From the resulting stress curve charts, it is fairly easy to
visualize the action of a rod using strictly the taper measurements.
Stress curve charts, or simply stress curves, are graphed as
follows. A rod's tip is represented on the left side of the graph along the X
axis, and the butt section is on the right. The Y axis contains the computed
stress along each point of the rod. Basically, the higher the point, the softer,
or more flexible, it is at that point on the rod.
Below is a chart for a Powell B8.7 straight taper - one whose
diameter changes a uniform amount of .0145" for each 5" along its length.
Compound tapers are ones that are not straight tapers, or ones
that gently widen or thin at various points along the length. Almost all bamboo
rods are built off of compound tapers.
As an example, a fast action rod is one that has a relatively
soft tip and a stiffer butt section, where most of the rods flex is in the
uppermost section(s) of the rod. A faster action bamboo rod stress curve chart
would look something like the graph for a Dickerson 8013 below.
A 'parabolic' rod is one that has a relatively soft tip, a
significantly stiffer mid section, then softens up again in the butt section.
The ubiquitous Paul Young Para 15 is an excellent example of this type of
action.
Below is another rod action that is called 'parabolic'. The shared
characteristic with the Young parabolic rod above is obviously the relatively
soft butt section. However, this Pezon et Michel Ritz Fario taper lacks
any softening in the tip section. This basic curve shape is also seen in the
few Payne parabolic rods that exist. To me, and in keeping with the
general patterns of stress curves, this shape would be better described as
'slow' action.
Garrison used his stress curve charts to create wonderful
medium, or progressive action rods. Garrison found that tapers with smooth,
horizontal stress curves generated this type of action. Here is an example from
a Garrison 209:
One of the variables that is used in computing a stress curve
is the 'length of line cast' or simply casting distance. By adding a Z axis to the standard stress curve
chart, one can see when a spot on a rod will become under- or overloaded. Here
is an example of the Dickerson 8013 from above with the addition of the line
cast from 2' to 50':
With a good working knowledge of stress charts, and a lot of
casting and comparing different types of rods, one can quite accurately predict
what a rod will be like by the shape and extremes of its graph. One can also
fairly easily create a new taper from scratch, or modify an existing taper to
suit a particular situation or remedy a perceived deficiency by using Garrison's
stress curve mathematics.
© 2009
Far North Rodsmiths
