The Aire and Calder tried to work with the railways when they arrived in the 1840s, by making traffic agreements, but still suffered a significant drop in trade. Receipts dropped by one-third between 1851 and 1856. Thomas Hammond Bartholomew, the chief engineer, had been experimenting with steam power since 1813, and steam paddle tugs had been operating on the system since 1831. When he died in late 1852, two-thirds of the traffic was pulled by steam tugs. His son, William Hammond Bartholomew, replaced him and introduced tugs with propellers soon afterwards. These could tow ten keels, carrying 700 tons, but were held up at locks, as the keels had to be worked through one at a time. Between 1860 and 1867, the locks from Goole to Castleford were extended to to alleviate this.