USS Pampanito - The Propulsion Plant

PROPULSION PLANT

Four main diesel engines turn generators which supply power for the electric propulsion motors, or to charge large storage batteries. The submarine is always operated by electrical power, the engines do not turn the shafts directly. When the submarine is on the surface, electric power is supplied by the generators and when submerged, power is supplied by the batteries. There are four propulsion motors, two connected to each of the two shafts through reduction gears. The reduction gears reduce the motor speed of approximately 1,300 revolutions per minute (rpm) to the propeller speed of 280 rpm. The next class of submarine, the Tench class, used two low-speed double-armature motors hooked directly to the shafts.

Illustration of general equipment layout.

MAIN GENERATORS: Four main Elliot generators produced 1,120 kw at 720 rpm, and 900 kw at 650 rpm. There is one generator coupled to each of the four main diesel engines. A single main generator, or any combination, can be used to charge the main storage batteries or power the main propulsion motors.

AUXILIARY GENERATOR - One Elliot generator rated at 300 KW. The auxiliary generator, powered by the auxiliary engine, supplies power for all auxiliary circuits, charges the main storage batteries at a low rate or can be used to power the main propulsion motors through the batteries.

MAIN ELECTRIC MOTORS - Four main Elliot motors rated at 1,375 horsepower each.

DIESEL ENGINES: Four main Fairbanks-Morse 10-cylinder opposed piston 38D - 8 & 1/8" two-cycle diesel engines. Opposed piston engines have two pistons arranged in opposite positions in each cylinder connected to crank shafts at the top and bottom of the engine. As the pistons travel toward each other they compress the air between them. At their closest point the space becomes a combustion chamber as fuel is injected. The resultant expansion caused by combustion pushes the pistons apart which causes the crank shafts to rotate. The upper and lower crank shafts are connected by a vertical drive gear. The main engines produced 1,600 horsepower at 720 rpm, and 1,280 at 650 rpm.

AUXILIARY ENGINE: one 7-cylinder Fairbanks-Morse opposed piston 35A - 5 & 1/4" diesel engine.

BATTERIES - Two 126-cell storage batteries. Each cell is 15" deep, 21" wide, 54" tall and weighs 1,650 pounds. Each cell is made up of positive and negative plates made of lead, each with common terminals, separated by insulators. The plates are immersed in an electrolyte solution made up of pure water and pure sulfuric acid with a specific gravity of 1.250 when fully charged. Each cell produces approximately two volts and are permanently wired in series. Each of the two battery groups could be operated independently or in parallel. The batteries could deliver approximately 5320 amps for one hour, 930 amps for ten hours or 235 amps for forty-eight hours. This means that the submarine could travel submerged at 9 knots for one hour or could travel 95 miles at a speed of 5 knots before the voltage falls to a limiting voltage. TOTAL SHAFT HORSE POWER: 5,400 surfaced, 2,740 submerged.