Marine turboelectric drive
Marine turboelectric drive was an advance in the design of steam turbine power systems. In the 1910s, the United States Navy built a series of turboelectric drive warships but ended production because of cost and treaty prohibitions on such heavy vessels. These efforts revived during World War II. The technology continued to be used in steam-powered commercial and passenger vessels in the following decades until the development of gas turbine engines in the 1960s.
The turbines on steam-powered ships traditionally provided direct power to the motor. Boilers created steam, which was sent to the turbines that operated on the head of the propeller shaft. As the turbines rotated, they moved the propeller.
The HMS Dreadnought, which entered into service in the British Navy in 1906, was the first battleship to use direct drive steam turbines, and revolutionized this field of war. Dreadnought had two paired sets of turbines. Each had a separate engine room and drove two shafts.
This system was very efficient at generating mechanical energy. Its major flaw was the way it paired a high fuel-efficient rotation—the turbine—with an inefficient rotation rate—the propeller. Waste was inevitable when the propeller was operated too slowly or too quickly.
Another important problem of direct-drive steam turbines was their vulnerability in the event of attack. Because they proved to be highly complicated mechanical systems, they demanded a lot of room. For one thing, they need multiple turbine stages to achieve fuel-efficient cruising speeds, high speeds, and backing power. They also needed specialized gearing to prevent turbine damage when the ship backed up. Combine that with all of the steam pipes needed to send power throughout the ship’s mechanics, and the direct-drive turbine system was left susceptible to damage in many places and left less room to hold weapons.
The turboelectric ship addressed the problems of efficiency, flexibility, and survivability. Instead of providing direct power from turbine to propeller, the turboelectric drive used a two-stage mechanical to electric process. First, like its predecessor, the turboelectric drive used boilers to build steam and move a turbine, and returned wasted steam to a condenser for reuse. Second, the turbine drove one or two electric generators, rather than the propeller shaft. The electricity from the generator was sent to electric motors mounted on the propeller shaft heads, powering the propeller at their most efficient rate.
As a result, turboelectric drive allowed for the most efficient use of both turbine and propeller. The turbine could enjoy a constant, highly efficient rotation without having to abruptly slow down or speed up and risk damage. The propeller could be operated flexibly in response to changing conditions. Importantly, marine engineers did not have to find space for all the steam piping demanded by a separate reverse stage. The electrical motors attached to the propellers could be easily reversed. Furthermore, the system was more survivable than direct drive. It could be compartmentalized better, making it less vulnerable to damage in the event of battle damage or accident. It was also quieter that direct drive, which made it an attractive technology in passenger vessels.
The Battleship USS New Mexico, launched on March 23, 1917, was the first capital ship employing turboelectric drive in the American fleet. The technology was adopted in a series of ships, but its use was interrupted in the 1920s in an effort to comply with international treaties limiting the gross weight tonnage of warships. Turboelectric drive systems were significantly heavier than direct drive turbines. Nevertheless, the technology proved fundamental to the future of marine engine design.