I have very little information on the DUNBOYNE herself, just that related to Ernest Prather who served as her master before transferring to the SANTA MARGARITA.
I know she was the first ship to receive an Armed Guard crew (CO was Ensign Brinn) and that under Prather, she was part of PQ-13 a convoy that suffered losses on the way to Murmansk.
Have you obtained the Armed Guard voyage reports, the various ship's logs or the convoy reports? You can also look for the Cargo reports to shed light (sometimes) on the cargo being carried. The Immigration service also met outgoing and incoming ships and recorded information about the crews. You can get access to them via Ancestry. Com. A NARA archivist recommended that source. There is always the ship movement card, too if you need additional information about where the Dunboyne sailed throughout the war.
If not, they are all in The National Archives and Records Service, College Park, MD. You can order copies of the reports by date...but they cost and it takes a long time to get them. If you are close, you can set up a visit and have the reports waiting for you to read and copy yourself
Hope this helps.