Alger-class cruiser

Profile drawing of an early version of the Alger design, c. 1890

The ships of the Alger class were 105 m (344 ft 6 in) long between perpendiculars and 105.5 m (346 ft) long at the waterline, with a beam of 12.98 m (42 ft 7 in) and a draft of 6.10 to 6.45 m (20 ft 0 in to 21 ft 2 in). They displaced 4,313 long tons (4,382 t). Their hulls featured a pronounced ram bow and a tumblehome shape, along with a sloped, overhanging stern. The ships had a minimal superstructure, consisting primarily of a small conning tower and bridge forward. Their crew varied over the course of their careers, amounting to 387–405 officers and enlisted men.[3][4]

Reports of the ships' rigging are mixed; according to Conway's All the World's Fighting Ships, the cruisers carried a pair of heavy military masts fitted with fighting tops for some of their light guns and observation positions. But in an article in Warship International quoting the 1905 edition of the Marine Almanac, Fisher states that the vessels were originally barque rigged, the sails being removed by the mid-1890s.[3][4]

The ship's propulsion system consisted of a pair of vertical triple-expansion steam engines for Alger and horizontal triple-expansion engines for Jean Bart and Isly, driving two screw propellers in all three vessels. Steam was provided by twenty-four coal-burning Belleville type water-tube boilers for Alger, while Jean Bart and Isly received eight of the older fire-tube boilers. Each ships' boilers were ducted into two funnels. Their machinery was rated to produce 8,000 indicated horsepower (6,000 kW) for a top speed of 19 to 19.5 knots (35.2 to 36.1 km/h; 21.9 to 22.4 mph). Normal coal storage amounted to 860 long tons (870 t), but up to 940 long tons (960 t) could be carried. This permitted a cruising radius of 3,200 nautical miles (5,900 km; 3,700 mi) at 10 knots (19 km/h; 12 mph) with the normal load, and 4,000 nmi (7,400 km; 4,600 mi) at the same speed with the maximum.[3][4]

The ships were armed with a main battery of four 164 mm (6.5 in) 28-caliber guns and six 138 mm (5.4 in) 30-cal. guns. All of these guns were placed in individual pivot mounts on the upper deck ; the 164 mm guns were in sponsons located fore and aft, with two guns per broadside. Four of the 138 mm guns were in sponsons between the 164 mm guns, one was in an embrasure in the forecastle and the last was in a swivel mount on the stern. For close-range defense against torpedo boats, they carried a pair of 65 mm (2.6 in) 9-pounder guns, eight 47 mm (1.9 in) 3-pounder Hotchkiss guns, and eight 37 mm (1.5 in) Hotchkiss revolver cannon. They were also armed with five 356 mm (14 in) torpedo tubes in their hull above the waterline.[4]

Armor protection consisted of a curved armor deck that was 50 mm (2 in) thick on the flat portion, increasing in thickness to 100 mm (4 in) on the sides, where it curved down to meet the sides of the hull. Above the deck, the ships had a 0.79 m (2 ft 7 in) wide cofferdam that was extensively compartmentalized to control flooding in the event of damage above the deck. The ships had 50 to 75 mm (2 to 3 in) plating on the conning tower. Isly and Jean Bart received gun shields that were 50 mm thick.[4]