BASIC FLY CASTING
Fly casting is easily described in the language
of physics if you understand how Newton’s first two Laws
of Physics and the Laws of Energy Conservation relate to the casting
of a fly line with a fly rod. Let’s look at each of these
immutable laws and simply apply them to the casting of a fly line
with the fly rod.
NEWTON’S FIRST LAW states that an
object at rest will remain at rest; an object in motion will continue
in motion with constant velocity, unless acted upon by an external
force. The three primary considerations that pertain to Newton’s
first law are Inertia, Force and Mass.
INERTIA is simply the tendency of a body
to remain at rest or if in motion in a continuous motion. In fly
casting it is the fly rod and fly line that are “at rest,”
until a FORCE of some type, is initiated upon the fly rod and
Generally speaking FORCE is simply a push
or pull that will change the velocity, (speed and direction),
of an object. In fly casting when we accelerate the fly rod we
are applying a force. The force that we apply to the rod comes
from the action of the casting arm. Without force the rod and
fly line will remain inert or at rest. Generally speaking the
control of the fly rod and line is totally dependant on the action
of the caster. As Vince Marinaro pointed out in 1976, in his book,
“In The Ring of the Rise,” “The rod cannot make
a cast any more than a baseball bat can hit a home run by itself.
It is the casters own muscle and energy that makes the cast.”
Finally, an objects MASS is measured by
its inertia. In this instance force is applied to the butt of
the fly rod by the caster and this becomes the action that in
turn overcomes the inertness of the fly rod’s mass and ultimately
fly line’s mass. Objects with greater mass have more inertia
to overcome. This is why a 10 weight outfit requires more applied
force to cast as efficiently as a 4 weight outfit.
NEWTON’S SECOND LAW basically states
that the more force we apply to an object the more it will accelerate.
Essentially Force (F) = Mass (M) X Acceleration (A). The more
massive it is the more it resists acceleration.
Before we examine the Law of Energy Conservation
it is important to note two additional energies or properties
that are potentially present in all fly rods and fly lines, that
relate to the understanding of how fly casting works.
When the caster exerts a force upon the
fly rod it will bend. The bending or loading of the fly rod is
really a storing up of energy known as POTENTIAL ENERGY. We call
it potential because it will later be transferred to the fly line
as Kinetic Energy.
When the rod unbends it transfers the stored
energy to the fly line in the form KINETIC ENERGY. Essentially
all objects in motion possess kinetic energy. So to, the fly line
moves with Kinetic Energy . The equation for kinetic energy is
K = 1/2M x V2 where M = mass and V = velocity. In his
book “Modern Fly Lines” Bruce Richards states that,”
The relationship between the whip and the fly line is obvious.
During a cast, a fly line unrolls just as a whip does. The bottom
part of the fly line ‘loop’, (the U shape of the line),
becomes stationary and the top leg of the loop accelerates. As
the mass of the moving part of the line,(the top leg), decreases,
it accelerates. As the line accelerates, wind resistance increases
geometrically, and the energy of the cast dissipates, slowing
the line and making possible a delicate delivery. It seems odd
that what allows a fly line to deliver a fly gently is actually
a very rapid acceleration of the line.”
Last but not least fly casting is governed
by the Law of Energy Conservation that states; Energy can neither
be created nor destroyed, but only converted from one form to
another. Basically energy from the caster is applied to the rod.
The fly rod in turn, because it is flexible third class lever
stores energy by bending at the tip first, in resistance to the
inertness or mass of the fly line holding it back. As acceleration
increases the resistance of the fly line will cause the rod to
bend further down from the tip and store more energy, until we
stop applying force to the rod. Once the caster stops applying
force to the rod it unbends or unloads and transfers the stored
energy of the rod to the now kinetically charged energy of the
fly line as it flips over the rod tip and begins to form the loop,
a standing wave propagation if you will, something like the waves
created by a wave machine at a water park only much more fun with
the fly rod. Well at least to me it is.
So there you have it, the basic physics
and principals behind fly casting. While this information has
no real practical use for teaching someone to fly cast you may
find an inquisitive mind out there one day who just had to know
how it all comes together.
P.S Our longest casts would be in a vacuum.
Who said vacuums weren’t any fun?
1. Force – Agency of change.
2. Energy- A measure of change imparted to a system. The capacity
to do work
3. Velocity – Speed with direction.
4. Motion – Velocity
5. Inertia- resistance to motion
6. Acceleration – The speed of the speed.
7. Mass- the amount of matter of an object as determined by the
8. Power- The rate of energy transfer.
9. Work – A necessary evil to be avoided at all cost.