If we want to cast the line a goodly distance then it makes sense to put a good deal of the mass at the front end of the line where it will be most effective. This, unsurprisingly, is called a weight forward line. Most of the mass is concentrated in the first forty or fifty feet of line, meaning that maximum power is achieved with only part of the fly line airialised. The rest of the line will shoot out when the line is cast. This idea is taken a step further by doing away with the thin back end of the line - called the running line - and attaching this shortened line directly to the backing line. This is called a shooting head and is identifiable by the fact that it is only a third of the length of a normal line. The third type of line in common use has a thin front end and then a uniform thickness for most of its length followed by a thin back end. Because this line spreads its mass over a greater length, it will not cast as far but can be used for delicate presentation at close quarters, making less of a splash as it lands. Because it is thin at both ends it is called a double taper line. The best way to understand the differences is by looking at the diagram, which shows the relative diameters of each line. Now let’s explore these lines in more detail.
The fly line is what sets fly fishing apart from all other methods of angling. In other forms of fishing, the bait or lure is cast using some type of weight with a monofilament or braided line. In fly fishing it is the weight of the line itself that provides the motive force to propel the fly through the air. The fly line has to have a certain amount of mass to carry out this task. This means that the fly line is not going to be inconspicuous in the water, so a length of ordinary fishing line is attached to the front end of the fly line to put distance between the fly line and the fly. This normal piece of line is called the leader, which is so important that it deserves a whole chapter to itself.