For ages, instructors have search the best metaphor to explain the loading of rod. For me, the best one is without any doubt the bow and the arrow.
For a beginner, the most difficult part to understand is that he must not throw is fly but load the rod and let it drives the line. The bow image is the easiest way to show them the concept. To launch an arrow you just have to draw the string and then release the both. The farther you bring the string back and the fastest the arrow will fly. The relationship between the loading and the power of the arrow is very effectively shown.
Now the caster has to transpose this image to the rod and line. The rod is flexible enough that the weight of the line will bend it but the truth is that the energy of this tiny weight moving in the air will create the load. In spey casting, the role of anchoring the D Loop is easier to grasp. The fix point restrains the line and loads the rod. By the way, it is the right time to enhance the importance of a strong anchoring. More, without anchoring, there is no spey cast.
And this fulfil the imaging, the line bends the rod, the rod springs out the line, the line drives the leader and the fly goes.
The rod is fast
The rod and specifically the tip of the rod go fast. Yes you can cast the line without a rod and Mel Krieger was playing at this in his courses but your hand will never keep apace with the rod. It’s a maths problem, you hand moves one foot the tip of the rod straight will move for 5 feet and with the flex it gives about 7 ‘. If the speed of your hand is 1 km/h at the tip it is 70 km/h. Believe me for the calculations and just keep in mind the speed.
If the caster let the rod go down forward or backward, the inertia of the rod and line will slow it down. The only way to keep the pace and even speed it up is to load the rod more with double haul. As I’ll explain in the “turbo single hand casting”, the idea of creating slack in the line with small loops is to break the inertia barrier and win some more speed.
The second part of the bow metaphor is the direction. Nobody can imagine that if I draw the arrow straight at me, it could, by any magic, go to the left. Why it could be the case for fly casting? The arrow will follow its own direction which shows no more than the mediatrice of the bow bend. to cast at a fish, I must backcast exactly opposite to it. If I speycast, my D Loop mediatrice is the direction of my cast. That is the 180° law for Simon Gawesworth, the world renown speycasting guru. This great teacher has two laws the 180° and the parallel one. Don’t interchange them. When you anchor your line, you have only one direction to cast which is parallel to the anchor that the first law. If you get outlaw, you’ll tangle. The second law is the 180°, if you don’t respect it you’ll lose your power. They are closely related but don’t proceed of the same error.