Gibb, 'I don't see how that would work for the chanty. Reading it closer, I think the crew was perhaps just walking the slack, after which, in positions, they did a pull in place. What do others think?

I read the same as you here.

Why does the author in 1858 not use the term "chanty"?
I didn't think the term was in wide universal use until later. Not everyone would be familiar with it. The writer is also speaking as a very observant outsider, not someone actively involved. He was simply observing, not talking to the crew.