Gentleman, Ladies:

Humbly: Not focusing on song "origin" here. That is elsewhere. I merely evoke those points to satisfy the reader that I've scratched one of his itches before isolating the subject by cleaving the other bits away.

My focus: The meter and timing of "Shenandoah" as a sailor chanty sung at the windlass.

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I tend to doubt Hugill having much to say about the song thay he didn't absorb from books. If it was "most popular of them all," and he was supposed to be the great Last Shantyman bringing his authentic shantyman wisdom to practice in the world, where are his performances of "Shenandoah"? Show us how it worked at the windlass, Stan.

This is the thing. Nobody uses "Shenandoah" in demonstrations of shipboard work. They steer far from it when invoking their old saw about "chanties providing the rhythm" because they have no clue about the rhythm. As a rubato, mixed meter or fermata-filled "ballad" (in the modern sense!), no one can envision it as a chanty and we basically have to pound people on the head with historical reference to try to persuade them it was (a chanty).
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I've always felt the initial stress should come on "SHEN" after a lead-in "Ohhh!" But then, I've never worked a windlass.
Possibly due to RR Terry's printing being the ultimate source (I guess) of popular/literate versions.

With so many noting DOAH on the downbeat -- and thus saving the first measure from having an "extra" beat -- it can't be ruled out. Maybe we have the whole "Shenandoah" thing wrong (*discussions from elsewhere!), and our getting stuck on imagining it the river/valley/etc name got us disposed to that stress emphasis on the first syllable.