(It would only be significant if we knew that "riding on a donkey" was a phrase actually used to mean "operating or employing a donkey engine."
There is no seafaring evidence that the phrase was *ever* used that way.
No memoirs, no collectors, no Stan Hugill. The only evidence we have is an assertion in a children's book in the 1930s, plus further assertions by landlubbers decades and decades years later.)


Could it be because there were no prizes for stating the bleeding obvious? :-)