Perhaps the simplest example with which to start is a tight loop.
Before we begin, we will make several assumptions: there is no slack in the line when the fly rod starts to come forward; the entire fly line is directly behind the rod tip as it starts to move; the fly line does not stretch; the fly line isn’t affected by gravity or wind; and when there is a change in direction, there is only one.
This example requires us to consider only two parts of the fly line: the end of the fly line (a short front taper, leader, tippet, and a small fly), and a section of fly line just outside of the rod’s tip top of five to ten feet. The tapered leader and tippet together are approximately nine feet. Basically, it’s not a long setup barely turning over for spooky trout on still water. It’s also not something that will recoil after turning over.
If the rod tip starts accelerating forward in a straight-line path, the end of the fly line begins moving at the same speed and in the same direction as the rod tip. As the rod tip accelerates smoothly, both sections of the fly line gain velocity at the same rate, and because the rod tip continues to move forward in the same direction, both sections of the fly continue to travel in the same direction.
When the rod tip travels in a single direction, without changing course, the rod tip and the entire fly line behave as a single object, gaining velocity as one unit. The rod tip accelerates the entire fly line forward in the most efficient way possible, and as a result, the end of the fly line reaches the highest conceivable speed in the forward direction (for those circumstances).
When the rod tip changes direction, however, the rod tip and the end of the fly line start acting as separate entities connected by a string.
Imagine a helium-filled balloon weighted with some perdigons to make it neutrally buoyant. In other words, the balloon just floats… not rising or falling. Imagine that this balloon is attached to several meters or yards of string. Essentially, we are replacing the fly with a balloon. When the rod tip pulls the balloon in a prolonged and straight path, as discussed above, the balloon’s speed and direction generally match those of the rod tip.
When the rod tip changes direction, however, the balloon’s velocity stops mirroring the rod tip’s speed and direction. For example, if the rod tip were to make an abrupt turn (continuing to accelerate but no longer moving in the forward direction), the balloon may be accelerated forward for a short period, but at a decreasing fraction of the magnitude had the rod tip continued forward in a linear path.
Changes in direction during the power stroke kill distance because the rod tip no longer pulls the fly line forward with the same force as a linear path – even though the rod tip may still be accelerating. In addition, the more the new direction of acceleration deviates from the original path, the more energy and distance are lost.
In the example with the balloon, moments after the rod tip changes direction, the string just outside of the rod tip would begin to move with the same speed and direction as the rod tip. And a few moments later, more of the string would have the same velocity as of the rod tip. But it would take a significant amount of time and distance for the rod to travel in the new direction before the balloon’s velocity would match that of the rod tip again: a duration and length where an expert power stroke may have already ended.
In the same way, when a rod tip changes direction just before the power stroke ends, there isn’t enough time to pull the entire fly line in the new direction. A late change in direction, due to its brief duration, mainly affects a short length of fly line just outside the rod tip: the line that initially forms the loop.
But, because the rod tip is no longer accelerating the fly line after the end of the power stroke, the rest of the line (where most of the mass is located), will continue to travel along the original path of the rod tip. The smaller mass in the initial loop can’t significantly affect the inertia of the fly line travelling in the original direction; and consequently, when the end of the fly line turns over, it will do so in a relatively straight path… along the original path.
In contrast, when a rod tip changes direction early in the power stroke, there is more time for the rod tip to pull more of the fly line (outside the rod tip) in the new direction. As more fly line gets pulled in the new direction, less line (and consequently, less mass) at the end of the fly line travels in the original direction.
When the power stroke ends before the entire fly line moves in the new direction, if most of the line is travelling in the new direction, the loop will turn over towards the new direction. What’s left of the end of the fly line that had been travelling in the original direction will be pulled towards the head of the loop causing the end of the line to jump across the rod leg of the loop as the end of the line turns over.
In this way, early changes in direction will make the loop look like its headed in one direction, but at the last second, the fly jumps to the side. At last weekend’s tournament, Ralph started talking about missing the yellow target at 45 feet. He lamented that the fly looked like it was headed towards the target, but his wrist must have turned at the end of the stroke, causing the fly to change direction at the last second. Yeah, no. Maybe he will read my blog.
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