In ships having two or more shafts, a fun-damental principle of engineering casualty con-trol is SPLIT-PLANT operation. The purpose of the split-plant design is to minimize damage that might result from any one hit.

Most naval ships built primarily as warships have at least two engineering plants. The larger combatant ships have four individual engineer-ing plants.

Split-plant operation means separating the engines, pumps, and other machinery so that two or more engineering plants are available, each complete in itself. Each main engine installation is equipped with its own piping systems and other auxiliaries. Each engineering plant operates its own propeller shaft. If one engineering plant were to be put out of action by an explosion, shellfire, or flooding, the other plant could continue to drive the ship ahead, though at somewhat re-duced speed.

Split-plant operation is not an absolute in-surance against damage that might immobilize the entire engineering plant, but it does reduce the chances of such a casualty and it prevents damage to one plant from being transmitted to, or seri-ously affect the operation of, the other plant or plants. Split-plant operation is the first step in the PREVENTION of major engineering casualties. The fuel oil system is generally so arranged that by means of fuel oil transfer pumps, suction can be taken from any fuel oil tank on the ship and the oil pumped to any other fuel oil tank. Fuel oil service pumps are used to supply oil from the service tanks to the main engines. In split-plant operations the forward fuel oil service pumps of a ship are lined up with the forward service tanks, and the after service pumps are lined up with the after service tanks. The cross-connection valves in the fuel oil transfer line are always closed ex-cept when oil is being transferred.

Although geared diesel propulsion plants are designed for split-plant operation only, some of the auxiliary and main systems maybe run cross-connected or split. Among these are the starting air systems, the cooling water systems, the fire-main systems, and, in some plants, the fuel and lube oil systems.

In diesel-electric installations the diesel elements are designed for split operation, but generator elements can be run either split or cross-connected.