The weight of such engines runs about 35-70 Ib/bhp(21-43 kg/kw of brake power High-speed diesels Many high-speed diesel engines of 600 rpm and more(some types originally developed for truck and locomotive service )are available for marine propulsion. Opposed piston types have been developed; other manufacturers favor a v type to reduce weight. Such engines are of two-and four-cycle types and usually weigh 10-40 lb/bhp(6-24kg/kw of brake power ) Because of less efficient scavenging, breaker power, and other factors, their fuel and lubricating oil rates are higher than for large, low-speed diesels Except for direct drive in moderate or fairly high-speed craft, marine applications of diesel engines or with diesel-electric drive to provide good propeller efficiency. Because their pistons, valves, and other components are small, standardized, and carried in stock, repairs are readily made, with the result that engines of this type are popular for no Oil consumption and starting Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings. In large engines this contamination is avoided by using piston rod-crosshead construction so that the crankshaft, connecting rods, and crossheads operate in a closed casing separated from the working cylinder. These engines are started and maneuvered by pressure from one or more reservoirs filled with air at about 250 psi(1.7 MPa). To make it feasible to start and readily reverse, two-cycle, single-acting marine engines should have at least four cylinders; four-cycle engines should have five or more cylinders Nuclear power Very successful installations of nuclear power have been made in submarines and a few surface ships Operation of the first nuclear merchant ship, the Savannah, was successful technically but not commercially. (The operating crew required special training, and it would be difficult to replace with only one commercial nuclear ship in service.) Mechanical reduction gears Reduction gearing for diesel and gasoline engines allows the use of a relatively high engine speed and lower more efficient propeller speed. Speed reduction ratios of 1.8: 1 to 4: 1 are common, preferably with helical teeth to give better wear and quieter performance. A reverse gear device often is incorporated in lowpower gears for astern operation. Other methods for providing reverse rotation use a direct reversing engine or a controllable-pitch propeller One, two, three, or four engines may drive the same gear through individual pinions. The use of a friction, electromagnetic, pneumatic, or hydraulic coupling serves to disconnect any engine. By reversing one or more engines, ready maneuvering, including astern operation, is provided for by the use of the respective coupling The high rpm(3000-9000) of modern marine steam turbine and the low revolutions of an effective propeller (as low as 80 rpm) require the use of two-stage gearing. Gear teeth of harder material than the gear. The gear trains are of the double helical, type to avoid heavy axial thrust. Double reduction gears are constructed with flexible couplings between the high-speed train and the low-speed elements Mechanical reduction gears are carefully constructed to close tolerances. They have forced lubrication in sprays ahead of the meshing teeth, to the bearings, and to the flexible couplings. Tests have shown that bearings represent at least half the power loss of the entire gear set Turboelectric drive This type of drive, comprising one or more steam turbine generators and ac propulsion motors, is al for ship propulsion. It was installed in many United States tankers during World War Il because of ava manufacturing facilities. The synchronous motors are provided with an induction winding for starting and reversing. Relatively large changes in propeller revolutions are made by alteration of the turbogenerator speed Motor, generator, exciter, and cooling equipment losses result in several percent lower efficiency than with geared steam turbines. Weights and costs are generally 25-30% higher than for the comparable turbine gear arrangement. Electric drive is not employed unless it offers significant operational or design advantages. These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motorThe weight of such engines runs about 35-70 lb/bhp (21-43 kg/kw of brake power). High-speed diesels Many high-speed diesel engines of 600 rpm and more (some types originally developed for truck and locomotive service ) are available for marine propulsion. Opposed piston types have been developed; other manufacturers favor a V type to reduce weight. Such engines are of two-and four-cycle types and usually weigh 10-40 lb/bhp (6-24kg/kw of brake power). Because of less efficient scavenging, breaker power, and other factors, their fuel and lubricating oil rates are higher than for large, low-speed diesels. Except for direct drive in moderate or fairly high-speed craft, marine applications of diesel engines or with diesel-electric drive to provide good propeller efficiency. Because their pistons, valves, and other components are small, standardized, and carried in stock, repairs are readily made, with the result that engines of this type are popular for nonoceangoing services. Oil consumption and starting Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings. In large engines this contamination is avoided by using piston rod-crosshead construction so that the crankshaft, connecting rods, and crossheads operate in a closed casing separated from the working cylinder. These engines are started and maneuvered by pressure from one or more reservoirs filled with air at about 250 psi (1.7 MPa). To make it feasible to start and readily reverse, two-cycle, single-acting marine engines should have at least four cylinders; four-cycle engines should have five or more cylinders. Nuclear power Very successful installations of nuclear power have been made in submarines and a few surface ships. Operation of the first nuclear merchant ship, the Savannah, was successful technically but not commercially. (The operating crew required special training, and it would be difficult to replace with only one commercial nuclear ship in service.) Mechanical reduction gears Reduction gearing for diesel and gasoline engines allows the use of a relatively high engine speed and lower, more efficient propeller speed. Speed reduction ratios of 1.8:1 to 4:1 are common, preferably with helical teeth to give better wear and quieter performance. A reverse gear device often is incorporated in lowpower gears for astern operation. Other methods for providing reverse rotation use a direct reversing engine or a controllable-pitch propeller. One, two, three, or four engines may drive the same gear through individual pinions. The use of a friction, electromagnetic, pneumatic, or hydraulic coupling serves to disconnect any engine. By reversing one or more engines, ready maneuvering, including astern operation, is provided for by the use of the respective coupling. The high rpm (3000-9000) of modern marine steam turbine and the low revolutions of an effective propeller (as low as 80 rpm) require the use of two-stage gearing. Gear teeth of harder material than the gear. The gear trains are of the double helical, type to avoid heavy axial thrust. Double reduction gears are constructed with flexible couplings between the high-speed train and the low-speed elements. Mechanical reduction gears are carefully constructed to close tolerances. They have forced lubrication in sprays ahead of the meshing teeth, to the bearings, and to the flexible couplings. Tests have shown that bearings represent at least half the power loss of the entire gear set. Turboelectric drive This type of drive, comprising one or more steam turbine generators and ac propulsion motors, is also used for ship propulsion. It was installed in many United States tankers during World War II because of available manufacturing facilities. The synchronous motors are provided with an induction winding for starting and reversing. Relatively large changes in propeller revolutions are made by alteration of the turbogenerator speed. Motor, generator, exciter, and cooling equipment losses result in several percent lower efficiency than with geared steam turbines. Weights and costs are generally 25-30% higher than for the comparable turbine gear arrangement. Electric drive is not employed unless it offers significant operational or design advantages. These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motor