The tip of the rod is what controls the fly line. The line just follows the rod tip so to speak. Ideally, when the line clears the water and becomes airborne, you should accelerate the back cast and then abruptly stop. This should provide enough energy to straighten the line out behind you. Just as the loop unrolls and the line becomes straight, you should accelerate the forward cast. This should provide enough energy to unroll and straighten the line out in front of you. Again, abruptly stop for a split second. In a slow motion you should allow the straightened line to fall to the water.
When you first begin the back cast by picking the line up off the water, the drag and weight of the line should bend or “load” the rod. When you begin your forward cast, the acceleration and weight of the line will again “load” or bend the rod in the opposite direction. When a rod is “loaded”, it becomes a spring. It is this loading and unloading of the rod that assist in casting the line. If it wasn’t for this fact, you may just as well use a very stiff rod. You could use a broom stick to cast the fly line and to some degree, the stick would work. If fact, you don’t have to use a rod at all to cast a fly line. You can do it with your arms. The fly rod just makes it easier to cast farther and more accurately. Again, the it is the loading and unloading of a fly rod that sends the line gracefully unrolling a good distance across the water. These are just basic principles of casting that many of you have probably heard many times.
Often, when we are making short cast, we fail to load the rod. That turns the cast into a sloppy presentation that spooks the fish when the line is picked up on the back cast as well as spooks the fish when the line hits the water on the forward cast. Even when you’re making a short cast, you still need to go through the procedures necessary to load and unload the rod. If done properly, when you make a relatively long cast, the loops formed on the back cast and the forward cast is in a relatively small plane. This narrow loop is called a “tight loop”. If you allow the rod to come back too far on the back cast, or go too far forward on the forward cast before stopping it abruptly, the loop formed will be in a wide plane or open loop. Open loops are not good for making long cast. When you are making long cast, you want to cast tight loops. One key objective in keeping a tight loop is to bend the rod progressively through the casting strokes in order to keep the tip of the rod traveling straight. Fast tip rods help accomplish this. If the rod tip travels in a big, wide arc, you will have a big, wide loop. You will be able to cast farther when you are forming tight loops.