I apologise, in advance, if this response is wasting your time.
While trying a quick websearch to see if I could find anything about this ship, I came across this photograph from 1938:
http://www.ingenious.org.uk/see/Transport/Aero nautics/?target=SeeLarge&ObjectID={C9A6EC15-C7 8A-0095-23C5-480752AC1EEC}&viewby=images
I note that the picture is part of the Daily Herald Archive, which is now held by the National Museum of Photography Film & Television, in Bradford. It occurs to me that press photographers rarely take a single picture on an assignment. There may well be other pictures, taken at the same time, which show the vessel in more detail and possibly include older members of the crew who may have served alongside your great uncle. If so, you might be able to access them through the museum.
Also, if a picture of the ship from 1936/37 would be of interest to you (and you don't mind forking out between �25 and �35 for a print), you can find one here:
http://rapidttp.com/museum/jmmc/jmmcw.html
(That site also contains the information that the vessel was scrapped in 1954).
More relevant, perhaps, is a 1926 photo of the vessel held in the collection of the National Maritime Museum:
http://www.nmm.ac.uk/server_process.php?show=c onWebDoc.596&outputFormat=pdf
Apologies again if I've wasted your time,
Chris