"a triple-stamp refrain"

What could that mean? Three syllables??

I don't get the use of "heavy haul" by these authors, either. A light haul is not an application for a chanty. As for "heavy" hauls, a topsail halyard haul is notably lighter than a fore sheet or "sweating." I could go on, but it just doesn't make sense and it sounds like someone making something up based on a vague imagination.

""New Grove Dictionary of Music and Musicians" (1980)"

Roy Palmer, maybe? Must have taken the "Dorian" from Lloyd's notes.

"But it does make a good work song"

Well, it IS a work song. It's just that the digging songs keep a steady beat. Nothing heavy about it, just constant energy, which is why the "bobbin" (chorus) is such a little thing, no big wind up (contrast Haul Away Joe).