A picture is better than a long explanation. The boat is long gone but its wake is visible for a very long time and forms a pattern looking like a trail on the sea surface. The two lines are not even divergent like the envelope of the wake. My first guess is that it is created by a change in refractive index of the water due to a non uniform mixing of the water temperature in the rear of the boat. But I can't explain why the perturbation is stable. It should diffuse or be conic as the wake of the boat.

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  • $\begingroup$ Clearly it greatly compressed the water and it can't return to its original shape until it rains :-p I joke. What a neat question $\endgroup$ Mar 20 at 4:14


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