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The ''Topaze''-class (often referred to as the ''Gem''-class) cruisers were a quartet of third-class protected cruisers built for the Royal Navy in the first decade of the 20th century. Four additional ships of the class were cancelled before their keels were laid. They were the last class of protected cruisers built for the Royal Navy. ==Design and description== Discussions had been had been ongoing for several years about a successor to the previous ''Pelorus'' class before the Admiralty decided on a design in 1901 that was very much larger and faster than the older ships. The ''Topaze''-class ships had a length between perpendiculars of , a beam of and a draught of . They displaced and their crew consisted of 313 officers and other ranks.〔Friedman 2012, pp. 198–211, 335〕 One objective for the Admiralty with these ships was to evaluate steam turbines against traditional triple-expansion steam engines in a ship larger than a destroyer and became the first cruiser to be equipped with them.〔Chesneau & Kolesnik, p. 84〕 Her three sisters used a pair of 4-cylinder triple-expansion steam engines, each driving one shaft, using steam provided by 10 water-tube boilers. The engines were designed to produce a total of which was intended to give a maximum speed of . The three ships easily exceeded their designed power and speeds during their sea trials.〔 They carried a maximum of of coal〔 which gave them a range of at and at .〔 ''Amethyst'' was fitted with a Parsons steam turbine set that drove three shafts using the same number of boilers as her sisters. They delivered enough steam to allow the engines to reach and her designed speed of . She also easily exceeded her designed power and speeds during her sea trials, reaching from . The turbine proved to be more economical than the reciprocating engines of her sisters, but less so at slow speeds, only having an endurance of at 10 knots, but at 20 knots.〔 The main armament of the ''Topaze'' class consisted of a dozen quick-firing (QF) .〔Friedman 2011, p. 101〕 One gun each was mounted on the forecastle and the quarterdeck. The remaining ten guns were placed port and starboard amidships.〔 Their shells were fired at a muzzle velocity of .〔 They also carried eight QF 3-pounder Hotchkiss guns and two above water 18-inch (450 mm) torpedo tubes.〔 The ships' protective deck armour ranged in thickness from . The main guns were fitted with gun shields and the conning tower had armour thick.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Topaze-class cruiser」の詳細全文を読む スポンサード リンク
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