I have it but it's on the boat, not available right now. I read it but
don't remember a discussion about what exactly causes prop walk. What
does it say?

Steve

That unequal blade thrust is the result of the difference in effective pitch
between the descending and ascending blade when a propeller is rotated on an
angle, (90 degrees from the angle at which the shaft exits the shaft log)
though a horizontally advancing medium (water under the boat).

(Page 143 in my 1985 edition, may be different in later versions)