Marc, I wouldnt argue with you at all, I'm no expert !! but just offering an explanation of the use of the phrase "Donkey Riding" as I've had it explained to me over the years.
Neither would I wish to be dogmatic in stating that a donkey engine would be steam powered ,just assuming that if the lyrics concerned pre-dated the developement of the Internal combustion engine they would of neccesity be steam powered!! I,m perfectly happy to be wrong, and bow to your expertise as a maritime historian.
the original explanation that I offered seems to be the commonly held one over here in the U.K, ( I,m assuming your in the U.S ) and I have heard it repeated many times,as well as seeingn it in print, although I cant recall where !!
Anyway its an interesting thread, and hopefully it will continue even if we never come to a definite conclusion.
Cheers !!