The P S Carrier or "floating railway" was originally designed as a vessel to cross the River Tay. However, when the Tay Bridge was built she was transferred to the Forth as a spare vessel. In point of fact, these vessels were very inefficient but were a fall back option. For example the P S Carrier was reinstated on the River Tay route following the fall of the Tay Bridge in 1879. Then in 1882 after the bridge's reconstruction, the Carrier was sold to IOWMTCo for the sum of £3,400 for use between Langston Harbour and the island berthing at St Helens.
Whilst construction of the ramps and winching equipment was being installed at both harbours in 1883 at a cost of around £30,000 - the Carrier was having some work carried out at Newhaven Harbour at the LBSCR marine workshops. As can be seen from the following drawings, the methodology of hauling the wagons on and off the Carrier was, to say the least, a tad impractical due to the varying heights of the tide at either end of the route.
The Carrier ploughed this route as and when it could, as the weather and sea conditions played a great part in its overall failure to make a profit and after only one year of operation the company was forced to make a sub-agreement with LB&SCR dated 23rd December 1885 for the hire of both the harbour's quays and the vessel. The service then continued until 1888, as again the new company had major problems with the route due to the erratic sea conditions and the design of the craft. One must not forget the River Tay is not the Solent and the normal calm conditions of the Tay are not often mirrored on the Solent. The last recorded trip was in March 1888 but there may have been others as she had been used in 1887 as a public viewing platform for Queen Victoria's fleet revue!