When Should You Accelerate the Rod During a Back Cast?
A common problem in fly casts is the line slapping the water behind the caster. It’s a problem that once plagued me, too. There may be fish behind us, but that’s not where we are fishing. Once you understand how timing of the rod’s acceleration during a back cast influences trajectory, you can eliminate this problem, too.
Most fly casts for freshwater fishing have front casts with somewhat downward trajectories. Since the ideal trajectory of a back cast is 180 degrees away from that of a front cast, the back casts for these typical distances should have an upward direction.
The back cast that we will discuss starts with the rod angled towards the target, and then it rotates to another position angled away from the target (Figure 1). To keep our discussion simple, the center of rotation remains directly below the vertical position of the rod, and the butt of the rod does not move up or down much during the cast.
What Happens If You Accelerate For The Entire Back Cast?
At some point in this arc, we need to start accelerating the rod in earnest, and continue accelerating it to a sudden stop. If we accelerate the rod continuously between the two positions of the rod in Figure 1, the tip of the rod forms a large arc, resulting in a wide, unwelcome loop. Consequently, the acceleration and momentary stop of the rod must compose only a portion of the arc pictured in Figure 1. For a given rod and distance, a smaller arc of acceleration, will generally lead to a tighter loop.
What Happens If You Accelerate In The Latter Half?
If the acceleration of a back cast starts and ends after the rod reaches a vertical position (i.e. in the latter stages of the back cast), the rod tip follows a downward arc (Figure 2). As the speed of the rod tip builds, the line is increasingly pulled downwards. At the end of the acceleration phase, when the rod’s counterflex finally releases the energy stored in the rod, the rod tip’s pathway has the most downward movement. Thus, it is late acceleration in the back cast (when the rod tip is moving downward) that drives the fly line into the water behind us.
Whether we realized it or not, we knew that late acceleration causes a downward trajectory. During a typical front cast, the acceleration of the rod starts just before or after the rod passes the vertical position. Then, the acceleration in the latter stages of the front cast, when the rod tip is on a downward path, creates a loop with a downward trajectory. The only difference that late acceleration creates in the back cast compared to the front cast is the direction of the line: one is accelerated down and away from the target while the other is accelerated down and toward the target.
What Happens If We Accelerate Early in the Back Cast?
When we think about possible arcs of acceleration that create an upward path for the rod tip, they occur in the early portions of the back cast (Figure 3). If late acceleration creates a downward trajectory, then early acceleration must create an upward trajectory.
Short acceleration arcs at the very beginning of the back cast create the highest trajectories. Slightly later arcs of acceleration that end before the rod tip reaches the vertical position, result in back casts that are still directed upwards, but with lower trajectories.
To form a tight upward loop, the acceleration of the rod must stop before the rod tip stops travelling upwards. This means that the acceleration must start early… as soon as all slack in the line has been removed. Consequently, the back cast is very much a controlled explosion of energy, launching the line into the air (against gravity). A great deal of torque is required to make a good back cast, and a shorter rod makes this task easier to accomplish.
The Bottom Line
The term, “back cast” invokes an image of casting the line behind us. Intuitively, it makes us think that acceleration should occur late – once the rod is behind us. In reality, a back cast is an upward stroke. We must start accelerating the rod early, while the rod is in front of us and the rod tip is still travelling upward.