In the past (before 9/11) they used to offer engine room tours, but very sadly, since that time nothing of this sort is offered. I've been fortunate enough to have taken those tours, and for someone who's even remotely interested in that sort of thing, it's fascinating! The size of the propeller shafts (on ships that don't use the pods for propulsion) is staggering, if nothing else, and the fact that the entire space is kept so clean, to me is amazing. You might express an interest to "those who might help you" ie: note who the chief engineer is at the welcome aboard show, and if you see him out and about, strike up a conversation.
Good luck, and maybe you'll be lucky enough to see the inner workings of a modern cruise ship.