HULL OF STEEL Improvements in the hulls of steamers were introduced steadily while machinery was being improved, principally with the idea of increasing the strength and carrying capacity and reducing the weight of hull necessary. Iron had shown itself to be superior to wood in these respects, and the next step forward was the intro duction of steel for shipbuilding. In 1876 a small steel paddler was built for river service in Burma and in the following year the British Navy built two fast dispatch vessels, the "Iris" and "Mercury." The first sizeable merchant ship to be so built was the "Rotomahana," a ship of 1,777 tons built by Denny on the Clyde for the Union Steamship Company of New Zealand in 1879. Within a few months she was followed by a very much bigger and more important ship, the Allan Liner "Buenos of 4,005 tons for the Canadian mail service. Although it was recognised that steel offered advantages in every direction except, possibly, durability, to begin with its general adoption was checked by the difficulty of obtaining supplies, but in the early eighties this was overcome and many steel ships were laid down.
The form of the hull was also the subject of numerous experi ments in the constant effort to increase the carrying capacity on the same or smaller tonnage, and for this reason several revolu tionary designs were brought forward. One of the most striking and permanent of these was the turret deck steamer which was evolved and built by the Doxford Shipyard of Sunderland. In this type a curve in the side above the water line gave a narrow deck with a broad extreme beam, and for some time it permitted a great economy in dues.
The "Turret" of 1892 was the first ship of this type and was laid down by Messrs. Doxford on speculation but bought by Messrs. Peterson Tate & Co. for the Canadian trade. Other steamship lines took up the turret deck steamer enthusiastically, particularly the Clan Line, but many of its advantages were negatived by the amendment of port and canal regulations and although these steamers were capable of carrying a very large cargo and were excellent seaboats if properly treated, in inex perienced hands they were apt to give trouble and they gradually fell out of favour.