Dolphin Nose Experiment

It is raining cats and dogs. Perfect weather for some indoors simple experiments.
I am delighted with the HS video capability of my new Lumix LX7: 100 fps at Full HD. A maximum aperture of 1.4 allows to shoot in very very low light. Fantastic.

For a number of years the fly casting world has been trying to explain the dolphin nose phenomenon. Some complex analysis relate it to the effect of air drag:

What if the mystery behind the dolphin nose had to do with the loop diameter imposing too small a turning radius for the line’s flexibility?

4 comments on “Dolphin Nose Experiment

  1. Bill Keister says:


    The Dolphin Nose – Nov 17

    I see something like the dolphin nose on some of my high power back casts. I have always thought of it as a Sheppard’s crock. I watch it start to develop as the loop is about half way unrolled. From this point it gets more extreme as the loop continues to unroll. During the first half of the unrolling loop process both legs of the loop appear to pretty parallel. During the second half the loop and a small portion of the legs close to the loop begin to climb. The rod leg has probably been climbing all along but has gone unnoticed for the first half of the process. As the Sheppard’s crock progress the distance between the fly leg and the rod leg progressively narrows. Usually the unrolling process ends before the two legs cross, but this is really an early stage tailing loop that may never complete.

    What I think is happening is that the fly leg is being pulled on a fairly horizontal trajectory. It wants to stay on that trajectory. The rod leg and the loop itself are on a slightly upward trajectory. But the mystery is why the loop doesn’t just get smaller and smaller. You suggested that it might be connected to the flexibility of the fly line. I don’t think that is the reason because I can throw six inch or smaller loops with the same fly line. But these are very low energy loops.

    The loop in question is a very high energy loop. The loop is a process. The individual elements of the loop are not going around the loop they are altering their trajectory by ninety degrees as reduce their speed so that they enter the fly leg perpendicularly. This creates, in aggregate, something that is, or at least operates like a centrifugal force which holds the loop open.

    So I think the dolphin nose occurs in high energy loop which due to their energy regime have a minimum radius and where the geometry of the two legs of the loop put them inside that radius.

    Bill Keister
    Theoretical Physics Hobbyist


    • Aitor says:

      Hi Bill,

      The dolphin nose is a mistery. At least for me. Some suggest that it is due to a decrease in tension in the loop. That makes sense for, in my experience, you get a dolphin nose when casting at low speed.
      However you say that you get them with high speed casts. Some video would be great.
      Anyway, IMHO, it doesn’t have to do with a tailing loop if we define a tail as a transverse wave resulting from an oscillation of the rod tip. A tail always appears before loop formation whereas a dolphin nose shows itself when the loop is “old”.

      Another amateur on physics. 😔


  2. Marc Fauvet says:

    hi Aitor and Bill,
    i wouldn’t venture an answer either. as Aitor points out DNs generally appear at slow casting speeds but i couldn’t help but think of this video where DNs are repeatedly crashing/collapsing when Bill mentioned them occurring with his distance casts.
    Lasse’s thoughts on this phenomenon are the cast was ‘hit too soon’.
    this may or may not be of help, i don’t know, but the video is always really cool to look at and i suspect there’s a correlation in there somewhere… 😀


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