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Old 01-09-2013, 01:28 PM
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Default The Physics of Fly Fishing

Reproduced and excerpted from DISCOVER. Article by, Curtis Rist

The type of rod also affects the speed and distance a line travels. Salespeople call some rods fast and others slow in describing how far they might cast a fly. Graig Spolek, a mechanical engineering professor from Portland State University in Oregon, set up an experiment to quantify these vague terms. He hauled a bundle of rods into a darkened gymnasium, set up a strobe light, and took a sequence of photographs to examine the movement of the rod and the line during the forward cast.

Rods have to be stiff enough to handle the lunges of a caught fish but flexible enough to transfer energy effectively from the arm to the line during a cast. This allows the tip to wiggle quickly back and forth, which Spolek calls the rod’s frequency. In another experiment, he counted how many times the tip of each rod moved back and forth per second, and this number, he discovered, allowed him to predict which rods would cast the farthest. High frequency gives you a faster tip speed, creating swifter line speed. “And that allows you to cast a long way,” Spolek says.

Still, Spolek was not satisfied. “Who cares about finding a unified theory of the universe?” he asks. “What we need is a unified theory of fly-fishing.” In 2006 he took a yearlong sabbatical to make progress toward that theory. In his research he deconstructed the mechanical limitations of the rod that cause its tip to swirl during casting, preventing the line from aiming true. To make a rod, manufacturers tightly wrap graphite-fiber fabric around a thin steel cylinder. Spolek found that if the manufacturers changed the way they roll the fabric, they could minimize the swirling problem. He also concocted a new way to measure the flexibility of fishing line leaders, the part of the line nearest the lure, using a technique he had previously developed to gauge the bending stiffness of the tiny wires in pacemakers. In this way, he discovered that newer fishing lines made of fluorocarbon were actually less flexible than standard nylon lines.

Of course, a perfect cast still depends on the skill of the person heaving the rod—but science is helping there, too. Noel Perkins, a mechanical engineering professor at the University of Michigan, has built a fly-casting robot that can imitate the casts of both experts and novices. His technology could enhance the sport of fly-fishing by permitting researchers to analyze the differences between casts. The end result could be better advice for newcomers to casting. And because the robot can cast repeatedly at the same angle and force, it can test fishing lines and rods objectively. Perkins and his team have also created a fly-casting analyzer that attaches to the reel. Using motion-sensor technology, it gives a detailed printout about the rod’s speed and angle over the course of a cast—feedback critical for casters to develop control over distance and placement.

In the meantime, Joan Wulff offers her own, starkly simple explanation for how she handles a rod with such flawless grace: “It’s all in the arm,” she says.

Discover Magazine: The latest in science and technology news, blogs and articles - The Whip-Like Physics of Fly Fishing
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