A few notes.

1 - The article did not take observed boat speeds and work backwards to make a correction fit. An approach was taken by which a different number was used in place of the standard 1.34, one method being to use hull length to beam ratio if I remember right. They then applied the approach to various different cats of the time to see how close it worked and reported the findings. In most cases it was fairly close.

2 - Don't know, but I don't believe the article was penned by a journalist. Of course, just because a journalist were to write something does not make it wrong. People with wonderful credentials can be just as wrong.

3 - The modification of the constant is in recognition that not all displacement boats get trapped by the wave system. Planing hulls climb over the bow wave, lighter displacement hulls with a narrow form cut through them. In this case the attempt is not to imagine that the wave system magically moves faster, by goblins or other means, but simply to characterize a hull type that doesn't get trapped. Is it an appropriate extension of the original formula then? Maybe not, but does that make it wrong? It probably tries to move towards a simplistic estimation of how the hull plows through the water regardless of the wave system using beam to length and displacement.

Anyway, out the cats I've sailed, all have greatly exceeded the traditional hull speed (using the traditional without the goblins method of calculation), and the only one that I would characterize as planing to any degree has been the I-20.

Of course, then there's the Farrier tris where the main hull has planing sections and the floats do not...