Yeah, I'm surprised by these numbers. I think trains might end up being more efficient in an "ideal" sense. The rails really help remove friction from the equation. TIL.

I suppose you'd have to factor in other issues in the "real" world, like managing inclines, curves, and starts/stops for traffic. Boats generally have fewer constraints on those fronts. Also, boats can increase their size in more than one dimension, which lets them increase size more geometrically and efficiently (trains can only get longer, and hits practical length limitations faster).