Chapter 25. -NEW DEVELOPMENTS IN NAVAL ENGINEERING 



combination of prime movers, various arrange- 

 ments are possible. The three combination plants 

 which at present appear to offer great advantages 

 for naval ships are (1) the combined steam and 

 gas turbine plant, known as COSAG, (2) the com- 

 bined diesel and gas turbine plant, known as 

 CODAG, and (3) the combined gas turbine and gas 

 turbine plant, known as COGAG. Other combina- 

 tions, including some that utilize nuclear power, 

 are also under consideration. 



Combined steam and gas turbine (COSAG) 

 plants have been installed in some combatant 

 ships of the British Navy and are being investiga- 

 ted by our own Navy. Figure 25- 10 illustrates the 

 general arrangement of one COSAG plant in- 

 stalled in a British twin-screw guided missile 

 destroyer; there are two such plants, each serv- 

 ing one propeller. Each shaft set consists of 

 a cross- compound steam turbine of 15,000 shaft 

 horsepower plus two gas turbines of 7500 horse- 

 power each. All prime movers drive into one 

 gear box. 



CX] 



CX] 



GAS TURBINES 



STEAM TURBINES 



147.167 

 Figure 25-10.— COSAG plant for one screw of a 

 twin-screw ship. 



A slightly different arrangement of a COSAG 

 plant is shown in figure 25-11. This plant, which 

 is installed in a British single-screw frigate, 

 consists of a single casing steam turbine of 

 12,500 shaft horsepower and one gas turbine of 

 7500 shaft horsepower. 



In both of the COSAG plants illustrated, the 

 steam turbine installation is capable of propel- 

 ling the ship at approximately 85 percent of full 

 power ship's speed, in the event of complete 

 failure of the gas turbine unit. The ability of the 

 gas turbines to make a rapid start allows the ship 

 to get underway very quickly with the steam plant 

 cold. Maneuverability (including reversing) with 

 the gas turbine is achieved by fairly complex 

 gearing and clutching. Each gear box incorpo- 

 rates a reversing sectionfor the gas turbine; two 

 manual clutches for the gas turbine, one for the 

 boost drive and one for maneuvering; a manual 

 clutch for the steam turbine; synchronizing 



clutches which automatically connect the gas tur- 

 bine drive to the main shaft; and two hydraulic 

 couplings which are used when maneuvering on 

 the gas turbine. With this arrangement, the steam 

 turbines or gas turbines (or both) can be used for 

 propulsion, and maneuvering can be accom- 

 plished either on the astern steam turbine or on 

 the gas turbine and the reversing gears. 



STEAM TURBINE 





CAS TURBINE 



147.168 

 Figure 25-11.— COSAG plantfor one- screw ship. 



Combined diesel and gas turbine (CODAG) 

 plants utilize diesels for the base- load plant and 

 gas turbines for the booster plant. The use of 

 multiple diesels and multiple boost gas turbines 

 means that the loss in ship's speed will be very 

 small in the event of failure of any one or even 

 any two units. The ship can get underway very 

 quickly with either diesel or gas turbine power. 

 The efficiency of the diesel is much higher than 

 the efficiency of a steam plant, and (for small 

 sizes of engines) the specific weight is somewhat 

 less. In general, CODAG plants appear to be suit- 

 able for ships which have moderate requirements 

 for cruising power, 



A combined gas turbine and gas turbine 

 (COGAG) plant has been proposed. Such a plant 

 would combine a long-life, efficient, moderate- 

 weight gas turbine for the base load and a light, 

 aircraft- type gas turbine for the booster load. 

 COGAG plants have not yet been tried out because 

 gas turbines suitable for the base loads are still 

 in developmental stages. 



CENTRAL OPERATIONS SYSTEM 



Advances in engineering technology, the use of 

 solid state devices, and computer circuitry have 

 made possible significant automation factors in 

 the operation of the naval engineering installa- 

 tions. Much of this automation has been applied 

 in the area of ship control and plant surveillance. 

 A general discussion is presented in this chapter 

 on a portion of an automated engineering plant 

 considered representative of those currently 

 being employed on naval vessels. 



639 



