Kiwi, it may be of some interest to you that at least one triple expansion engine has been recorded on film while at sea. Included in it are two separate shots showing the watchkeeper feeling both the top and bottom ends which has been a matter of discussion through this thread.
The filming was done in 1963 on the Balarr, which was engaged on the Australian Coastal trade.
Some footage of this film has been incorporated in a video produced by Des Cox of Snowbow Productions. The video is "Ships to New Zealand", (Part 5), Episode 22. There is also footage depicting the routine life on board an ordinary old cargo ship, both above and below decks as it was back in the 1950's, with shots of a Doxford engine probably not seen before.