There is some confusion over the vessels named Great Western which operated to Jersey because there were actually three ships with this name, but some histories omit the first, a paddle steamer which was active in the 1840s and '50s, although the actual dates of her construction and career are unknown.
However, this must have been an earlier vessel than the ship named Great Western I in Kevin Le Scelleur's Channel Island Railway Steamers, because he shows that vessel, also a paddle steamer, as having been constructed in 1867.