A self-teaching technique for calculating where and how much to mend the floating fly line. Cast & Observe:
“I tell beginners to try to read the stream and make their mends where they think they should go. Then after they have fished that lie, make several straight casts without mending to the same area. Don’t watch the fly. Instead observe the fly line and leader as the mismatched currents force curves into the line. The flyline will show you where the differential currents are, and the direction and depth of the curve shows you the differential velocity between the various currents. Now try to mend the line so that it is a direct opposite of the displaced fly line. Make a “mirror image” mend.”
SwittersB & Exploring 
http://www.bordergameangling.co.uk/Template%20Pages%20for%20new%20links/ThePileCast.htm
http://www.youtube.com/watch?v=-jB7ii0sx_g
Not the best explanation/instruction but, you get the idea…. A pile cast is best suited for downstream or slightly down and across presentations as opposed to across current(s). The slack plays out toward a straight line/leader/tippet. If the strike occurs with too much ‘pile’ either the fish hooks itself or your may be able to impart movement to the fly to set the hook by the traditional upstroke or by throwing a roll cast toward the fly/fish. A small pile is normally best.
LikeLike
A downstream mend is less common, so visualize the fly (faster water out there than closer to you)…the downstream mend(s) slow the fly from racing/hinging ahead too fast from the whipping action again. Best way to see this is get out there and cast out 20’+ of line and see what happens. Start with gentle mends, and bigger to see what happens…experiment.
Also, the drift may be short, requiring but one mend, or longer over good water, requring multiple mends to extend the drift. This is done by working extra line out through the guides and throwing upstream mends every few feet of drift.
Experiment, practice, look at the play of the currents on the fly line. Study the different flows before you before you cast. Study heavy flows and slower water beside. Find that seam on the edge of heavy to slower. Think why that would be a productive lie.
LikeLike
A few things: This concept is for when you aren’t fishing over rising fish. You are taking time to not worry about the fish, but rather practice casting on a stream/river and experiment a bit with the current(s). Eventually you will see the currents and cast/mend accordingly. Try to cast straight out for optimum results. Most often, you will see the fly moving slower (slower current speed) or just right, and somewhere in the middle a different current speed will cause the line to bow downstream at a faster speed. This then results in a whipping affect and the fly speeds up and drags across the stream. The fly is moving at a faster speed than the current, once the belly in the line causes the whip to go into action. This is not how a natural insect would look. Matching the hatch is not just finding a similar fly, but matching the actions of the real insect.
Practice the mends (usually upstream) without causing the fly to move. Practice, practice. Even experiment with downstream mends to see what it does to the movement of the fly. In effect, you are trying to keep the fly moving in the trout holding water, the bucket, the window, the seam at the same speed as the water. Think about the speed of a drifting insect and try to match it. Confusing, I know.
LikeLike