This painting was previously thought (by me) to be S.S. Amphion a steam cargo ship built in 1911 by the Campbeltown Shipbuilding Co. However with little knowledge of this subject I was pleased to receive an email from an experienced researcher who has suggested the boat is much earlier and could date from the 1850s/60s.
I think your picture might be even more interesting than you suggest. Even with a lay interest in maritime history this looks much older than 1911, nor is it the USS Amphion (ex SS Koln, 1899) (Google images finds both). Look at the auxiliary sailing schooner rig, stern form, gilded decoration and lack of superstructure in comparison to SS Great Britain. 2 open wheel positions would also be very early. So perhaps 1850s/60s. In 1868 the Dundalk Steam Packet Co replaced their wrecked SS Mystery with an SS Amphion (AB Swan, 1979, ‘The Port of Dundalk’).