If you ever tried casting large wind resistant flies using a typical trout fly line taper you probably found it difficult. Some of the reason has to do with how the fly line itself is shaped. Fly line shape is called its taper. It is how the diameter of the fly line changes from end to end.
Point – The portion of fly line in front of the front taper approximately six inches often including a welded loop made at the factory.
Front Taper – The portion of fly line in between the belly and the point. Changing in diameter from thick to thin from the belly to point respectively.
Belly – The portion of the fly line that is larger and level in diameter than the adjacent front and rear tapered sections.
Rear Taper – The portion behind the belly and before the running line.
Head – The combination of front taper, rear taper, and belly. Head weight increases with head diameter.
Running Line – The portion of the fly line at the rear beyond the rear taper. It is attached to the backing using a knot or loop depending on the manufacturer and application.
Loop – The shape of the fly line when travelling through the air, which is formed by casting.
Top Leg – The component of the fly line loop located at the top.
Bottom Leg –The component of the fly line loop located at the bottom.
Turnover – The transition of the top leg to the bottom leg.
The size and shape of the taper and belly determine how the fly is delivered to the target. Casting energy physically levers the top leg over. It transfers the casting energy and helps turns over the top leg and fly. As the fly line unrolls, extending towards the target, the top leg shortens, the bottom leg lengthens, and with it the fly is hurled through the air.
Various reasons, such as, wind resistance, weight of fly, and lack of line speed make turnover difficult but the appropriate head does solve for these challenges. Taper also determines how easily the line is to cast and mend. Generally, the longer the head the more false casting you need but the easier it is to mend. Contrastingly, the shorter the head the easier it is to shoot line, with less false casting, but the more difficult it is to mend.
Head turnover also pulls the fly. The energy is transferred from your casting stroke, through the rod, to the line and finally the head. Once the head is turned-over, the weight actually pulls the fly through the air similar to a rubber band used with a slingshot.
Fly line is an important component of your gear. Carefully choose the proper tool for the job at hand. Pick the right tool and your job becomes a lot easier.