Before dealing with the engines and their trials, it may be stated that the vessel is of 9000 tons displacement at 25 ft. 9 in. mean draught. Her length is 375 ft. and her beam 65 ft. She was built at Chatham, and the armament consists of two 92 in. 22-ton breech-loading guns, ten 6-in. 5-ton guns and sixteen 3-pounder quick-firing, and eight machine guns, with torpedo launching carriages and tubes. The propelling engines were manufactured by Messrs. Maudslay Sons & Field, Lambeth. They were designed to develop 13,000 horses with natural, and 20,000 with forced draught. They consist of four distinct sets of triple expansion inverted cylinder engines, and occupy with boilers, etc., nearly two-thirds of the length of the ship. They are placed in four separate compartments, two sets being coupled together on the starboard and port sides respectively for driving each screw. There are four high pressure cylinders, 36 in. in diameter; four intermediate cylinders, 52 in.; and four low pressure cylinders, 80 in.; with a stroke of 4 ft. Each set of engines has an air pump 33 in. in diameter and 2 ft. stroke, and a surface condenser having 12,800 tubes and an aggregate surface of 2250 square feet, the length of the tubes between the tube plates being 9 ft. There is also in each compartment one centrifugal circulating pump driven by a small independent engine, of the diameter of 3 ft. 9 in., and capable of pumping from the bilge as well as the sea. The screw propellers are 18 ft. 3 in. in diameter with a mean pitch of 24 ft. 6 in.
Steam is furnished by six main double-ended boilers, having four furnaces at each end, and one auxiliary boiler, with a heating surface of 900 sq. ft., the dimensions of the former being 15 ft. 2 in. by 18 ft., and of the latter 10 ft. by 9 ft. long. The total area of firegrate surface is 863 sq. ft, and of heating surface 26.936 sq. ft. Each engine room is kept cool by four 4 ft. 6 in. fans. Forced draught is produced by twelve 5 ft. 6 in. fans, three being stationed in each stokehold. The electric lighting machinery consists of three dynamos of Siemens manufacture driven by a Willans engine, each of which is capable of producing a current of 400 amperes. The after main engines can be easily disconnected and worked separately for slow speeds.
The Blake had her steering gear tested on Tuesday, Nov. 17. With both engines going full power ahead and turning to starboard, with her helm hard over 35 deg., she completed the circle in 4 min. 40 sec., the port circle being completed in 5 min. 5 sec. The diameter was estimated approximately to be about 575 yards. Forty-five seconds were required to change from engine steering to steering by hand. By manual gear the helm was moved from midships to hard a-starboard in 40 sec., from starboard to hard a-port in 2 min. 10 sec., and from hard a-port to midships in 2 min. 20 sec. The heavy balanced rudder and the speed of the ship throwing great labor upon the crew manning the wheels, the hand gear was afterward disconnected and the connection with the steering engine completed in 40 sec.
On Nov. 18, when the vessel went on speed trials, the draught of the vessel was 24 ft. 8 in. forward and 26 ft. 8 in. aft, which gave her the mean load immersion provided for in her design. There was a singular absence of vibration, said to be due to the space over which the machinery is spread, but perhaps also due, in part at least, to the number of cranks, as the cylinders deliver six throws throughout the circle of revolution. The results of each hour's steaming are as under:
| Hours. | Revolutions. | Steam. | Power. | |
|---|---|---|---|---|
| 1st | hour | 86.86 | 120.6 | 13,568 |
| 2d | " | 89.26 | 128.0 | 15,298 |
| 3d | " | 88.55 | 125.0 | 14,251 |
| 4th | " | 89.58 | 127.6 | 14,759 |
| 5th | " | 89.40 | 125.0 | 14,394 |
| 6th | " | 89.55 | 125.0 | 14,512 |
| 7th | " | 89.15 | 126.0 | 14,893 |
The trial was originally intended to continue for eight hours, but at the end of the seventh, as the light began to fade, and as, moreover, the engines were working with a smoothness and efficiency that showed no signs of flagging, it was considered expedient to terminate the run.
| Steam pressure in boilers | 125.50 | lb. |
| Air pressure in stoke holds | 0.42 | in. |
| Revolutions per minute, starboard | 88.41 | |
| Revolutions per minute, port | 89.39 |
| Starboard. | Port. | |||
|---|---|---|---|---|
| Forward | Aft | Forward | Aft | |
| Mean pressure in cylinders, high | 43.04 | 38.95 | 42.36 | 42.45 |
| Mean pressure in cylinders, inter. | 31.49 | 30.82 | 30.17 | 28.38 |
| Mean pressure in cylinders, low | 11.68 | 12.4 | 12.85 | 12.32 |
| Indicated horse power each engine | 3631.42 | 3589.07 | 3721.37 | 3583.50 |
| Total | 7220.39 | 7304.88 | ||
| Collectively | 14525.37 | |||
As will be seen, the collective power exceeds the contract power under natural draught by 1,525.37 horses, and was obtained with less than the Admiralty limit of air pressure. The coal used on the occasion was Harris' deep navigation, but no account was taken of the amount consumed. Four runs were made on the measured mile with and against the tide, the mean of means disclosing a speed of 19.12 knots. The average speed of the seven hours' steaming, as measured by patent log, was 19.28 knots. This fell short by over three-quarters of a knot of what was anticipated in proportion to the power indicated by the engines. Up to the limit of air pressure used the boilers answered admirably.