Morphing Loops and Dolphin Noses

 

DN marked

Photo by Álvaro González Santillán

 

Recently I have been asked about the dolphin nose, its cause, and more precisely if it should be considered a casting fault —for those who wonder what a dolphin nose is, I have highlighted one of them in the picture above.
Well, it seems that there isn’t a consensus among physicists and engineers about the reason for that weird line shape; some sustain that it is due to aerodynamics while some others say that it is a question of varying tension in the line.

Whatever its ultimate cause may be, in my experience the dolphin nose is something that happens when the loop is relatively narrow and traveling at relatively low speed. You can get them easily on every attempt with a snap cast:

 

The following is a gif made from a burst of high speed stills (20 fps). It shows how a perfectly rounded loop nose turns into a dolphin nose as the loop gets narrower and approaches complete unrolling.

DN

As you can see the loop itself changes its shape without any intervention from the caster.

So, to me, far from being a fault, the DN is the telltale sign of good casting technique; after all, beginners are more prone to wide loops and excessive energy than to the opposite.

As an aside, there are some interesting characteristics about waves to analyze in that gif above. Look at the small wave that gets formed by the counter-flex and rebound of the rod tip:

  • It propagates at the same speed of the loop (both keep their relative distance all the way).
  • It loses its amplitude as it loses energy.

That gives some keys about, for instance, the technique to send a curve mend up to the tip of the line. But that is stuff for some other article.

2 comments on “Morphing Loops and Dolphin Noses

  1. Eugene Geppert says:

    Is the small wave caused by counter-flex + rebound, or by rebound alone?

    Like

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