Interesting that although the writers like to use words like "plaintive," none seems to choose the words "minor" (or even "modal"). Once again, this may be an artifact of too few accounts, but it is certainly more consistent with Gibb's idea that "blue" notes were used rather than not. If some later shanty tunes are considered (I'm thinking of one or two of the "Sally Brown" tunes), the early writers could have meant "modal," but my guess is that musical education in the early 19th C. at least mentioned that modes existed or "used to" exist. Maybe a musicologist knows more about that likelihood.

If we had a hundred characterizations instead of just a handful, we might be able to draw a sounder conclusion.

OTOH, if the "blues" scale really is an African importation (is it for sure?), it would be perverse of African-descended rowers not to use it two hundred years ago.