Iris-class cruiser
The Iris class consisted of two ships, and, built for the Royal Navy in the 1870s. They were the first British all-steel warships.
Design and description
The Iris-class ships were designed as dispatch vessels by William White under the direction of Nathaniel Barnaby, Director of Naval Construction, and were later redesignated as second-class protected cruisers. The only visible difference between the sister ships was that had a clipper bow and was longer than with her straight stem. Iris was long overall while Mercury was long. The sisters had a beam of, and a draught of. They displaced at normal load and were the first British warships with an all-steel hull. Their crew consisted of 275 officers and ratings. The ships were not armoured but extensive internal subdivision gave them some protection against flooding, as did the double bottom under the propulsion machinery compartments.The Iris class was powered by a pair of horizontal four-cylinder Maudslay, Sons and Field compound-expansion steam engines that were configured with a pair of high-pressure cylinders with a bore of and a pair of low-pressure cylinders in diameter. All cylinders had a stroke. Each engine drove one propeller shaft using steam from eight oval and four cylindrical boilers with a working pressure of. The engines were designed to produce a total of for a speed of, which was handily exceeded by the sisters. Iris initially reached a maximum speed of from during her sea trials, but after new propellers were fitted, achieved from. Mercury became the fastest warship in the world when she made from. The ships carried a maximum of of coal, enough to steam at. They were initially fitted with a barque sailing rig, but this was removed after a few years.
The Iris-class ships were originally armed with ten 64-pounder rifled muzzle-loading guns, eight on the main deck and the remaining pair on the upper deck on pivot mounts to serve as chase guns fore and aft.