Thanks, Steve. I agree that Boston 1837 > Tahiti 1839 does not present an issue. The issue that is bugging me is where Dana fits in.

-My hypothesis is that the "Tally" chantey derives from the "Yankee Ship" song. There are similarities.

-"Yankee Ship" was "new" in May 1837 Boston. Here's the sheet music cover suggesting the dating of the song.

-Dana's voyage, out of Boston, started Aug. 1834. He returned Sept. 1836. It seems unlikely that "Yankee Ship" was composed early enough to be taken out to Spanish California and made a chanty by Dana's compatriots, or made a chanty ("Tally") and spread to Dana in time for him to have sung it before his return trip around Cape Horn.

-Yet, Dana adds it to his list of chanties sung. Suggesting to me either,
1) If he did sing "Tally," it preceded "Yankee Ship." The similarity of the two songs withstanding, "Yankee Ship" was inspired by the chanty!
2) Dana added it to his list, but he did not actually sing it. He became aware of the chanty afterwards. Which means the list of chanties in the 1869 edition of TYBM can't be trusted!

Looking for a reason to avoid 1) and 2)!