I have seen lots and lots of references to the formula "X times
square root of waterline length" as defining hull speed with X
normally about 1.3 (speed in knots, length in Imperial feet.)
However, I have never seen an explanation of this.

Pictures of boats "trapped" between their bow and stern waves seem
to make sense. But they do not explain why a long wave would travel
faster than a short one.

Surely there is a book with the theory?


Thank you,
Sakari Aaltonen