I have posted the real explanation of what the Auld Triangle actually was on one of the other threads related to the song...The Auld Triangle was not in fact anything to do with the Joy itself, but was in fact the sound of the metal triangles used by the working boats on the Royal canal. They would make deliveries to the warehouses that ran on the banks opposite the prison, as a warning of a delivery or pick up. These deliveries were at six in the morning and six in the evening, so gave the men inside an idea of the time. Within the context of the song, it also represented a link to the normality of the outside world to the prisoners incarcerated within.