The
Powerful class displaced at normal load. They had an
overall length of , a
beam of and a
draught of . As they were intended for overseas service their steel
hulls were sheathed in wood to prevent
biofouling. The hull had a
double bottom and was subdivided into 236
watertight compartments. At deep load,
Terrible had a
metacentric height of while
Powerfuls was . Their designed complement consisted of 894 officers and
ratings, the largest crew in the RN at that time. The ships were propelled by a pair of vertical inverted four-cylinder
triple-expansion steam engines, each driving one
propeller, using steam provided by 48 Belleville boilers with a working pressure of . These were the first cruisers in the Royal Navy with four funnels. Their engines were designed to produce a total of using
forced draught for a maximum speed of . The ships reached a maximum speeds of from during their
sea trials. They normally carried of coal which gave them a range of at , but they had a maximum capacity of , the largest coal bunkers of any ship in the RN at that time.
Armament and protection The main armament of the
Powerful-class cruisers consisted of two 40-
calibre BL Mk VIII guns in single
gun turrets, one each fore and aft of the
superstructure. The mounts could elevate up to +15° and the guns fired a projectile with a
muzzle velocity of to a maximum range of . Their secondary armament of a dozen 40-calibre
quick-firing (QF) Mk I or II guns was arranged in
casemates
amidships. The end casemates were the first two-storey (guns on the
main and upper decks) casemates in the RN. The guns had a maximum range of at an elevation of 15° from their shell at a muzzle velocity of . For defence against
torpedo boats, sixteen
12-pounder () 12-cwt guns were fitted. Eight of these guns were mounted in embrasures at the ships' bow and stern on the main and upper decks and the remaining eight guns were placed amidships on the upper deck. Their shells had a range of at an elevation of 20° at a muzzle velocity of . The ships were equipped with a dozen
3-pounder () Hotchkiss guns mounted in the pair of
fighting tops on the
military fore and mainmasts. Two additional
12-pounder 8-cwt guns could be dismounted for service ashore. The ships also mounted four submerged
18-inch (450 mm) torpedo tubes, a pair on each
broadside. The ships generally used
Harvey armour. The gun turrets were 6 inches thick on their face and sides, with a roof. Their barbettes and the casemates were protected by 6-inch armour plates and the latter had rear plates. The
conning tower was protected by plates. They had a curved armoured deck that had its crown in the middle of the ship above the
waterline, and the edges were below the waterline. The deck was thick over the machinery, thick over the
magazines, and thick in the middle of the ship. The bottom of the protective deck was only 2.5 inches thick.
Modifications After completing their sea trials, the funnels were heightened by to improve the draught of the boilers. Mark I
Wireless Telegraph (radio) sets were installed in each ship in 1900–1901. The ships were refitted in 1902–1903 and four more six-inch guns were added in casemates amidships at that time, although no additional ammunition could be accommodated. The three-pounders were removed from
Powerfuls upper fighting tops in 1904–1905 and both ships were fitted with
fire-control equipment in the upper fore and lower main tops in 1905–1906. All of
Terribles three-pounders had been removed by 1910, but
Powerful retained her remaining guns as late as February 1912. The torpedo tubes were removed from both ships in 1914. ==Ships==