A puzzle solved
Remember this picture?
I posted about it here, and wondered which ship the old ship of the line was. A commenter sugested HMS St Vincent, which I had considered but ruled out because by the time the picture was taken the St Vincent was permanently moored at Haslar near Portsmouth and being used as a training ship. However, thinking of training ships gave me some more ideas for search terms, and before very long I found this article about HMS Impregnable. Impregnable went though a number of changes of role, ending up in 1888 as a quarantine hulk for use in an epidemic. At this point her name was given to HMS Bulwark (which had started out as HMS Howe - I hope you're taking this in as there will be a short test later). In 1891 HMS Bulwark was renamed as HMS Caledonia and moved to Queensferry (by the Forth Bridge) for use as a training ship.
Here is a picture of HMS Impregnable (formerly HMS Bulwark, formerly HMS Howe) around 1900. It certainly looks like the same ship.