In a comment here I wondered what a canal boat was doing as far up the Liffey as Grattan Bridge in 1873. Here is a report from the Freeman’s Journal of 10 March 1875 that may provide a possible explanation.
THE LATE WRECK IN THE RIVER LIFFEY:— The porter-laden canal boat which was swamped on Monday by being borne by the flood in the river against the southern abutments, at the western side of Grattan-bridge, still remains in the place where she sank. Though she came with great force against the structure, she did not inflict the slightest injury upon it. Measures will be at once taken for floating the sunken vessel, which does not in any way interfere with the river traffic, as the centre arches are quite clear. All the porter which was on board the canal boat when she went down has been secured.
Remember that Guinness built its wharf on the Liffey in 1873 but did not start building its own fleet of barges for the Liffey until 1877. It did, however, have “a few small tugs” that were used to draw laden boats.
Guinness had easy access to the Grand Canal Harbour at James’s Street, so it seems unlikely to me that Grand Canal boats would risk the Liffey passage to supply pubs along the Grand, the Barrow and the lower Shannon. It therefore seems more likely that the boats were either Royal Canal boats or were being used to supply ships in the port.