Although Melville had argued for triple screws (for which he had advocated since the 1890s), the twin-screw arrangement of the Pennsylvanias was retained.
Two four-cylinder vertical triple expansion engines, located in separate watertight compartments, supplied a combined total of 23,000 indicated horsepower at 120 revolutions per minute.
Diameters of high- and low-pressure cylinders were in the ratio of i to 7.3: High Pressure 38.5 inches (0.98 m); Intermediate Pressure 63.5 inches (1.61 m); Low Pressure, 2 of 74 inches (1.9 m).
Piston stroke for all cylinders was 48 inches (1.2 m).
Sixteen Babcock & Wilcox straight water-tube boilers, sub-divided into eight watertight compartments, supplied steam at a pressure of 265 psi (1,830 kPa) at boiler, 250 psi (1,700 kPa) at engine.
These had a combined grate surface of 1650 square feet and a heating surface of 70,940 square feet.
Forced draft was on the closed fire-room system.
The ships usually carried 900 tons of coal but could hold a maximum of approximately 2,000 tons, which gave them a range of approximately 6,500 nautical miles at a cruising speed of 10 knots and approximately 3100 nautical miles at full speed.

Design speed was 22 knots (25 mph; 41 km/h).
Despite Melville's concern about insufficient power, all four ships performed higher than expected during trials in both horsepower and speed.
Each ship went through its speed trials in two stages, a four-hour run at flank speed and a 24-hour endurance run at the maximum maintainable speed.
Although Melville had argued for triple screws (for which he had advocated since the 1890s), the twin-screw arrangement of the Pennsylvanias was retained. Two four-cylinder vertical triple expansion engines, located in separate watertight compartments, supplied a combined total of 23,000 indicated horsepower at 120 revolutions per minute. Diameters of high- and low-pressure cylinders were in the ratio of i to 7.3: High Pressure 38.5 inches (0.98 m); Intermediate Pressure 63.5 inches (1.61 m); Low Pressure, 2 of 74 inches (1.9 m). Piston stroke for all cylinders was 48 inches (1.2 m). Sixteen Babcock & Wilcox straight water-tube boilers, sub-divided into eight watertight compartments, supplied steam at a pressure of 265 psi (1,830 kPa) at boiler, 250 psi (1,700 kPa) at engine. These had a combined grate surface of 1650 square feet and a heating surface of 70,940 square feet. Forced draft was on the closed fire-room system. The ships usually carried 900 tons of coal but could hold a maximum of approximately 2,000 tons, which gave them a range of approximately 6,500 nautical miles at a cruising speed of 10 knots and approximately 3100 nautical miles at full speed.
Design speed was 22 knots (25 mph; 41 km/h). Despite Melville's concern about insufficient power, all four ships performed higher than expected during trials in both horsepower and speed. Each ship went through its speed trials in two stages, a four-hour run at flank speed and a 24-hour endurance run at the maximum maintainable speed.
Tennessee-class cruiser