We call dolphin nose to a very characteristic shape taken by the fly leg of the loop. Its origin seems obscure to me, but Grunde Lovoll (fly caster and Ph.D. in Physics) says that it is the result of a decrease in tension in the fly leg of the loop during unrolling.
In my view one thing is for sure: the dolphin nose is not a shape that you see in the casts of beginners, quite the contrary, it is something reserved to those who can generate narrow, slow moving loops. I don’t see how a narrow loop with no more energy than that needed to completely unroll could be considered a fault, so, consequently, I don’t see the dolphin nose as the result of any casting error whatsoever.
Look how a very low line speed (not enough for a complete turn over of the leader) results in dolphin noses.
The shape of a dolphin nose being akin to that of a tailing loop may lead to confusion. There are fundamental differences, though:
- A dolphin nose appears after the loop has been formed.
- Consequently, a dolphin nose is not the result of an anomaly in the path of the rod tip during the casting stroke, as it is the case with tailing loops.
- The wave of a tailing loop is formed before the loop is born, so that wave is present before the casting stroke ends, and can be seen propagating along the fly leg during the whole flight of the line.
See below a clear example of the formation and propagation of a tailing loop.
And here a dolphin nose produced by an almost rigid “rod”. Since the rod doesn’t bend that shape can’t be result of an anomaly in the path of the rod tip.