The best way to cast depends on several key factors. One factor is how many flies you are fishing, whether they are weighted with beads or lead, and how they are distributed on the leader. Heavy flies or split shot add point source masses on the leader and this disrupts the turnover of the leader.
Now add a indicator and you have not only added another weight, but also another point on the leader with disruptive aerodynamic drag.
When the flies are unweighted and the indicator is small, casting is not difficult. When the indicator is large and the flies heavy, you can end up in a mess.
These point sources of mass and air resistance means the path of the fly line ahead of the leader has less control of the leader. Rather than following the path of the fly line, the heavy flies and indicator try to follow a ballistic path. They will want to go in direction they were going at the stop. When the flies and the indicator are not on the same tract as the fly line at the rod stop, you can get a tangles leader.
If you are casting a heavy nymphing rig, the most important piece of advice I can give you is to AVOID false casts. You will have difficulty getting that leader to go around the loop because the weights want to keep going in a straight line. Even if you make just a single back cast and a forward cast, those flies and indicator will disrupt the smooth loop and make each following cast more difficult because the fly line, the leader, and flies will become further off tract with each subsequent cast. Each casts adds more opportunity for a tangle,
When casting heavy rigs, do a water haul/tension cast. This is a forward cast WITHOUT any backcast. Let the fly line, leader, indicator and flies drift past you and straighten below you. Then you use the tension of the flowing water to straighten your leader and your fly line below you and you make a single forward delivery cast.
Here is how it is done:
At the end of you drift, point your rod downstream at your line and allow the line, indicator and nymphs to straighten downstream. The amount of line that is down stream will determine the extra load BUT it also determines how far the cast will go. If you have too much line, you will not be able to cast it all upstream even with the extra water load. If you have too little, you are limiting the distance cast. So you need to titrate the amount of line, meaning you need to experiment to see what is the optimum amount of amount of line for the maximum load you can use.
In a single smooth motion, cast the line toward your target. Make sure the loop is wide enough so that you don't hit your rod with the indicator or flies. That would be bad. Try a wide loop first and then you can narrow it as you get better at the cast.
The cast is best done at 180 degrees from the the downstream line position. Sometimes the downstream line position will be such that you cannot cast upstream to the point you want to. You can then make the upstream cast as best you can, then immediately pick up and cast back downstream to where your need to to make another upstream cast to your target.
Secondly, you can haul and shoot line on this cast. The amount of line you shoot varies with how effective you are with the water load and the haul.
The effectiveness of the cast varies with the fly rod you are using. Depending on the weight being cast, some fly rods will wimp out. They will not be stiff enough to propel the cast. So give it a try but be careful you do not over stress your fly rod.
So when the distribution of flies, split shot, and indicator makes standard casting unworkable, resort to the water haul/tension cast.
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