In every form of fishing with a rod, whether it be a simple pole, a spinning rod, a bait casting rod, a fly rod, etc., a line is somehow “attached” to the rod, and a “hook” is tied to the other end of the line. In all but one of these forms of fishing with a rod, the “hook” and/or any associated weight, is tied to a “weightless” line. This line is usually nylon monofilament (or something similar), and is what the uninitiated generally call, “fishing line.”
The weight that is tied to this fishing line, whether it be a hook, lure, bobber, sinker, split-shot etc., is then (in essence) “thrown” using the rod as an extension of the angler’s arm. And since the “weightless” line is tied to this weight, it is pulled out right along with it. The angler can then use this line to retrieve their hook, hopefully with a fish attached. This “throwing” of the weight that carries the line out is known as a “cast,” and most anyone can easily understand how it is accomplished.
But in one form of fishing with a rod, the typical “weight” is relatively weightless, and can’t be thrown any distance. So the cast is accomplished in a completely different manner, and this form of fishing with a rod is known as fly fishing.
If you have ever tried to throw a feather, you know that it doesn’t go very far, and it certainly can’t pull a fishing line along with it. But in essence, throwing a feather is what you are trying to do when you attempt to cast a fly, and this is especially true if it is a dry fly, which is all we really care about here anyway.
They say that necessity is the mother of invention, and that is likely the case when it comes to fly lines. Sometime far back into fly fishing’s past, someone developed the idea of using a line that could be cast by itself, and this “heavy” line would be able to pull the “weightless” fly right along with it, instead of the other way around.
Now the western U.S. is known to have some of the greatest fly fishing in this country, and it also just happens to have something else typically associated with it that can help us understand the principles required to cast this heavy line: cowboys. Yes, believe it or not, cowboys (or more correctly a “tool” they use, can help us to clearly understand this type of casting.
Let’s assume for a moment that we have just tied one end of a short (maybe a foot or so) piece of kite string to the end of a cowboy’s leather bullwhip. And to the other end of the kite string we tie a small feather. Now if the cowboy (or you) “crack the whip” the kite string and feather will simply go right along for the ride.
Now to crack the whip, the handle of the bullwhip is moved in such a way that it causes the heavy leather “line” of the bullwhip to form a loop (or wave) that rolls out from the handle of the bullwhip all the way to the tip. Upon reaching the tip this loop “whips around” quickly, and you hear the cracking of the whip, which is actually a small sonic “boom.”
But if you had caused the same loop to rollout much more slowly, the heavy “line” of the bullwhip would still roll out to the tip, where it would then give a small “flick” to the kite string and feather, and then it would simply fall to the ground in a straight line pointing away from you. Now if your bullwhip happened to be ten feet long, then your feather would now be at least ten feet away from you. Or in other words, it has just been “cast” ten feet. But you didn’t throw the feather, you cast the line.
Now we don’t use bullwhips and kite string to fly fish with, so fly lines with sufficient mass were developed for the very purpose of forming a loop that will roll to the end of the line and carry a weightless fly along with them. First these lines were made from horsehair, or something akin to it. Then came silk, (which is still used today) and later from modern textiles (plastics).
The above image shows (left to right from the finger) a size 16 dry fly hook followed by a loop of 14 lbs. test (0.014” diameter) nylon monofilament (the inner loop). The middle loop is a silk fly line (3 weight), and the outer loop is a plastic fly line (3 weight).
Using the rod, the angler causes their fly line to form a loop that unrolls in the air, and then gently settles to the water, delivering the “hook” (fly) that is attached to the end of this fly line. The fly is attached to the “heavy” fly line by using a short length of “weightless” line known as a leader. A leader is not exactly the same, but in principle it is very similar to the kite string we used to attach a feather to the bullwhip, and it is often made from (you guessed it!) nylon monofilament (fishing line).
Hopefully, you now understand how in fly fishing, you are actually casting the fly line, and not a “weight” that is tied to the line. And as you can see, the principles used in fly casting are the exact opposite of all the others.
Since fly fishing is the only form of fishing with a rod that requires you to cast the line and not the “weight,” this is what separates it from all the other forms of fishing with a rod. You can also make the argument that this difference is one of, if not the main reason, why fly fishing is also the most challenging form of fishing with a rod.
The unique nature and challenge of fly fishing appeals to many, but certainly not all anglers. Obviously, it appeals to me. I simply consider it to be the most appealing (and challenging) form of fishing with a rod there is, and dry fly fishing is the absolute pinnacle of this casting application.