U.S.C.G. Polar Star Combination of a Diesel Electric Propulsion Plant with a Geared Gas Turbine Boost Plant

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1 73-GT-73 $3.00 PER COPY $1.00 TO ASME MEMBERS The Society shall not be responsible for statements or opinions advanced in papers or in discussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. Discussion is printed only if the paper is published in an ASME journal or Proceedings. 73-GT-73 Released for general publication upon presentation. Full credit should be given to ASME, the Professional Division, and the author Is). Copyright 1973 by ASME U.S.C.G. Polar Star Combination of a Diesel Electric Propulsion Plant with a Geared Gas Turbine Boost Plant A. F. FINIZIO Marine Applications Engineer, Turbo Power and Marine Systems, Inc., Farmington, Conn. The paper is a progress report on the selection and design of equipment for the U.S.C.G. Polar Icebreaker. A discussion of equipment concepts, designs, and modifications to off-the-shelf equipment is presented with a review of major design problem areas and solutions. The various modes of operation of the combined system with the attended degrees of flexibility and limitations of each are also defined. Contributed by the Gas Turbine Division of The American Society of Mechanical Engineers for presentation at the Gas Turbine Conference and Products Show, Washington, D. C., April 8-12, Manuscript received at ASME Headquarters January 11, Copies will be available until February 1, THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS, UNITED ENGINEERING CENTER, 345 EAST 47th STREET, NEW YORK, N.Y

2 U.S.C.G. Polar Star Combination of a Diesel Electric Propulsion Plant with a Geared Gas Turbine Boost Plant A. F. FINIZIO INTRODUCTION The United States Coast Guard Icebreaker, POLAR STAR, WAGE-10, will be delivered in The 400-ft, 11,000-ton vessel is the first icebreaker designed and built by the United States since 1954, and is slated for duty in the Arctic and Antarctic. The 60,000-shp POLAR STAR, designed by the U. S. Coast Guard, will have a 100 percent increase in ice penetration capability over that Length (overall) 399 ft-0 in. Length on design waterline (28 ft- 0 in. waterline) 352 ft-0 in. Beam, molded, maximum 83 ft-6 in. Draft, design icebreaking (molded). 28 ft-0 in. Displacement 10,863 tons Shaft horsepower installed per shaft a Diesel engines 6,000 hp b Gas turbine 20,000 hp Total of the current Coast Guard "WIND" class icebreak- a Diesel engines 18,000 hp ers. The vessel's characteristics are: b Gas turbines 60,000 hp Aft 4*;* COAST GUARD 1,..1[Ney ' Fig. 1 USCG Icebreaker POLAR STAR, WAGB-10 (artistis conception) 2

3 Fig. 2 Cutaway propulsion machinery sections c Gas turbines (overload capacity) 75,000 hp Maximum cruising range at 13 knots. 28,275 miles Endurance, full power days, diesel mode 38 days Sustained sea speed, diesel mode knots Icebreaking ability, maximum ice thickness Continuous at 3 knots speed of advance 6 ft Ramming 21 ft Diesel fuel capacity (95 percent). 1,352,400 gal Officers, crew, and scientists 165 The POLAR STAR, under construction at Lockheed Shipbuilding and Construction Company, represents a major departure in United States icebreaker propulsion plant design. Employing a CODOG system (combined diesel or gas turbine) and three controllable reversible pitch propellers, the icebreaker will have one and a half times the power of the Soviet Union's LENIN, presently the most powerful icebreaker afloat. The selection of the CODOG propulsion system to power the new icebreaker was made after several ship design studies by the Coast Guard determined that a CODOG system offered the best alternative for icebreaker service. The advantages of the system include: 1 Reduced crew for operation and maintenance functions 2 High horsepower capacity without on-the-line reserve 3 High system flexibility and availability. The CODOG system, in itself, is a departure from standard design using a combination of diesel electric propulsion drive with a mechanical gas turbine-reduction gear drive system. The diesel electric a-c generated, rectified to d-c drive system is the icebreaker base load or cruise plant, while the gas turbine boost plant is used to power the icebreaker in thick ice fields. The two independent systems drive common shaft lines with CRP propellers. The propulsion motor armature becomes a part of the line shafting during gas turbine operation. The combined propulsion systems with the CRP propeller improve the overall vessel operation by providing: 1 Most efficient operation during cruise and normal icebreaking operation 2 High efficiency of a-c generation with the fine control and excellent low-speed torque capability of d-c drive 3 Propulsion prime mover crossover capability in the diesel electric drive 4 Ability to maintain shaft rpm by propeller pitch reduction during excessive loading to minimize propeller damage more likely to occur at low rpm's 5 Maximum horsepower available on immediate standby. Because of the complexity and interdependency of the propulsion equipment and control functions, the shipbuilder was required to select a prime 3

4 MACHINERY LIST 0 PROPULSION MOTOR PROPULSION DIESELGENERATOR 0 REDUCTION GEAR 0 SHIP SERVICE DIESEL GENERATOR MARINE GAS TURBINE Fig. 3 Plan view machinery layout 3 A 26 2A Is IA PROPULSION DIESEL GENERATORS The overall technical resolution of various engineering problems has been accomplished by an engineering team, consisting of Lockheed Shipbuilding and Construction Company, Turbo Power and Marine Systems, and J. J. Henry Company with approval of the United States Coast Guard. 0 RECTIFIERS PROPULSION BASE LOAD PLANT i _L- GENERATOR -7- T 7 7 SET-UP SWITCHES PROPULSION 2 MOTORS CASUALTY POWER NORMAL POWER Fig. 4 One line diagram diesel electric propulsion drive system vendor to provide the major components of the main propulsion and ship's service systems and to act as Propulsion Systems Manager for control integration and interface of the icebreaker machinery plant. The design and selection of equipment and systems has emphasized several concepts including: 1 System reliability and flexibility 2 Modularization for minimum installation, interface, and shipboard maintenance requirements 3 Standardization of all components for increased availability and maintainability, and minimum spare parts inventory 4 Minimum equipment envelope 5 Off-the-shelf equipment or design. The base load plant of six diesel-driven a-c generators produces 600o shp at each propulsion d-c motor to drive the three controllable, reversible pitch propellers. The diesel electric plant provides power for free route or open water conditions, and for icebreaking up to 4-ft thickness. In the diesel electric mode, the cruising range of the vessel at 13 knots will be more than 28,000 miles. The icebreaker will have a sustained speed of 17 knots on the diesels. The diesel electric propulsion plant has been designed primarily as three separate shaft systems. However, sufficient crossover capability and equipment redundancy has been included to ensure a high degree of system flexibility and reliability. System crossover capability has been designed into the system so that each of the propulsion motors may be powered by either or both of the diesel generator sets that provide normal power or casualty power from one diesel generator set from each of the other shaft systems. The casualty mode diesel generator sets may only be used separately or in combination with one of the diesel generator sets producing normal power. The generator combinations are selected for each motor through a motor-operated generator set-up switch as illustrated in Fig. 4. 4

5 Through the availability of additional propulsion exciter regulators, equipment redundancy also contributes to system flexibility. Each shaft set of generators has a spare or standby exciter-regulator that can be switched to either generator. One standby exciter-regulator is provided for the three propulsion d-c motors. Thus, the total system includes nine generator exciterregulators and four motor exciter regulators to ensure the maximum degree of system reliability. Critical systems, such as the shaft lube oil system, have duplicate pumps which also ensure the system reliability. The primary concern in the selection of the diesel and design of the diesel generator sets was a unit size consistent with the physical constraints of the vessel while still meeting the specified horsepower rating. In order to meet this requirement, the diesel generator set was designed to incorporate all engine auxiliaries, except the jacket water expansion tank on the engine skid. The resultant prepackaged diesel generator set has the added benefit of minimizing installation and interface requirements within the vessel. The total diesel generator module resulted in an envelope just under 29 ft in length and 8 ft in width. The final design also allowed all engine maintenance to be performed within the diesel generator set envelope, further reducing the required area clearances for equipment removal. Selection of the diesel was based on the requirement for each unit to produce 3000 shp at the propulsion motor output flange. The final diesel rating could not be determined until preliminary design had been completed on the major electrical components, i.e., a-c generator, rectifier, d-c motor, and associated line losses. Therefore, for selection purposes, a preliminary rating of 3500 bhp was selected. The final rating of the diesels has been calculated to be 3450 bhp (Fig. 5). As the propulsion control system design evolved, it became apparent that the number of variables was far greater than perhaps on any other ship afloat. Control of a shaft system in the diesel electric mode required the integration of diesel speed, generator regulation, motor regulation, and propeller pitch schedule. In order to reduce the number of control parameters, it is being proposed to govern the diesel in speed steps rather than as the typical variable speed marine unit. Although this type of governor control is unfamiliar to the marine industry, it is often used in industrial applications employing a diesel electric a-c-r-d-c system similar to that of the icebreaker. The preliminary diesel gov- EFF.99.3% 2479 KW > DIESEL 3323HP GEN 2395 NW 2388 KW' 23 I K 3500 HP 2140 KW 70 KW CABLE IIMRPM.96 PF 0 5KW LOSS 150' SW LOSS DIESEL 0HP 100 RPM EFF 96 6% 695VAC 98 PF 1074 AMPS 1 EFF 99 4% 2574 KW 3450HP GE N 2474K 2463KW 2449KW 2740 KW F.96 PF 1 _g:sto'e 0.5KW SW. LOSS 7 EFF 96.I% 565 VAC.96 PF 1400 AM PS, KW CABLE LOSS 60' -4.01M CABLE LOSS 60 m Kw 2368KW moo Hp 2444 K EFF 94.5% 900 V DC 5270 AMPS SYSTEM AT 100% CURRENT (EFFICIENCIES BASED ON TWO DIESEL MODE) DC MOTOR 6000 HP EFF V DC 6851 AMPS SYSTEM AT 130 % CURRENTIEFFICIENCIES BASED ON TWO DIESEL MODE 2238 KW 3000HP Fig. 5 Diesel electric drive system rating and losses erning schedule has limited the diesel operation to two speed steps, the first at 900 rpm for noload to 9/11 of full power, and the second at 1100 rpm for full power. The diesels will be started, stopped, and idled at 400 rpm. Limiting the control of diesel speed to two speeds allows a further reduction in the degree of control variables by reducing the propulsion generator exciter control to two simple isochronous schedules triggered by engine speed. Although a primary guide in the system design was to use off-the-shelf equipment designs, the electrical propulsion system equipment embodied sufficient new requirements to necessitate special design efforts. Some of the salient design aspects are discussed in the following. The totally enclosed propulsion generators are six-phase, a-c synchronous generators. The six-phase generator design, consisting of two separate three-phase "Y" circuits, was used to reduce the rectified d-c ripple and to minimize the current per phase. Additional d-c ripple reduction was accomplished by only displacing phase separation by 30 deg. The generators are normal rated at 2610 kva, 0.97 P.F. at 700 v, 1074 amps to produce a rectified 900 vdc. During overload icebreaking conditions, each generator is also continuously rated at 1400 amps, 130 percent of rated current, at a reduced voltage of 565 v to produce the rated output at the motor shaft. The single armature marine type d-c propulsion motors are rated at 6000 shp at 900 vdc. Each motor is capable of transmitting full power from 105 to 130 rpm. As with the propulsion generators, the motors are rated for a continuous

6 4110 4i !40 e : : ' A E, Fig. 6 Preliminary main propulsion control console mock-up current of 130 percent of rated current with the reduced voltage to produce 6000 shp during the most severe icebreaking conditions. The continuous 130 percent current, rating cf both the propulsion motors and generators has been specified to protect the units, while maintaining full load horsepower during excessive ice loading. In a major departure from standard large marine motor designs, the motor is double-ended to interface with the propulsion shafting on the after end and the reduction gear shaft disconnect coupling on the forward end. Using the standard motor design of a forged flange on one end and a keyed flange on the other, the overall motor shaft length precluded the installation of the shaft brake, creating a severe space problem within the icebreaker. Since the use of a keyed flange coupling was precluded by space limitations, the only solution was to provide forged flanges at both ends. However, this solution necessitated a major redesign of the spider and commutator sections. An overall shaft length savings of 18 in. was accomplished. Although the motor bearings and foundation were electrically insulated in accordance with standard practice, a full electrical loop still existed due to the motor being double-ended. The loop passes through the propulsion shafting and propeller, through the water, back to the motor shaft through the ship structure and turbine reduction gear. At least one side of the loop had to be insulated, but insulation of the shaft couplings or reduction gear bearings was deemed impractical, if not impossible. Hence, in order to break this loop, a grounding circuit was employed on the inboard side of each bearing connected to the ship's structure. This scheme provides an electrical loop running inside each of the motor bearings isolating the propulsion shaft system bearings from induced eddy currents. BASE LOAD SYSTEM SETUP AND CONTROL Propulsion Set-up Switchboards, one for each shaft system, are located in the Engineering Control Center (ECC). The switchboards control the selection and setup of the electrical propulsion equipment. A mimic panel is incorporated on the switchboards to allow the operator to follow the equipment selection sequence and make immediate equipment status evaluations. The control functions on the switchboards are interlocked to prevent improper equipment selection. 6

7 ALOFT CONNING CONSOLE d BRIDGE WING CONSOLE PILOTHOUSI CONSOLE BRIDGE WING CONSOLE d d d ddd d ALOFT CONSOLE PILOT/WING CONSOLES 0 0 DIESEL GEN SETA DIESEL GEN SET B FUEL MARINE CONTROL SAG H TURBINE pj;, CONTROLLABLE PITCH PROPELLER PITCH THRUST SERVO BEARING MAIN CONTROL CONSOLE d dd PROPULSION MOTOR SHAFT DISCONNECT COUPLING REDUCTION GEAR MARINE GAS TURBINE ) MAIN CONSOLE DIESEL/ELECT MODE SPEED FIELD CONTROL EXCITER P- 0 V DC ED OVERLOAD,CONTROL RE IUECATFP N DC MOTOR TACH PROPULSION DIESEL/GENERATORS PITCH CONTROL TRANSFER II-BOPSI VALVE 1 Fig. 7 Typical throttle control schematic Control transfer switches are used to transfer the diesel generator control functions to either one of the two motors that a generator can power. The control transfer switches are interlocked with the generator set-up switches to ensure that the Main Propulsion Control System throttle will properly control the selected diesel generator and motor combination. When operating with two units per shaft, the diesel generator sets will be paralleled on the d-c side of their associated rectifiers. The static, solid-state exciter-regulators include a load balancing circuit that automatically equals loading of the two generators supplying a given motor. The generator exciter-regulators also include a residual magnetism 'killer field." This provision is required to prevent arcing across the generator set-up switches during mode transfers from one to two or two to one diesel generator sets per shaft. Both the motor and generator exciter-regulators automatically maintain constant horsepower and current overload by decreasing voltage proportionally as current increases up to a maximum of 130 percent rated armature current. The overall propulsion control electronics are centered in the Main Propulsion Control Console. The control console is programmed, at this time, to control propeller pitch, propeller speed, generator field, and diesel speed in response to movements of a single lever control for each shaft system. The control console is divided into an operating section and a monitoring section. The primary functions of the operating section are: V DC PITCH SERVO 45PSI Fig. 8 Basic control system schematic os CIANN. 1 Remote start-up and shutdown of prime movers and propulsion auxiliaries 2 Operating mode selection 3 Single lever control for each shaft 4 Remote control transfer. The shaft control lever section of the console is essentially duplicated in remote control stations at the pilot house, bridge wings, and aloft conning station. Transfer of remote control is from the control console to the pilot house. The pilot house may, in turn, transfer control to the aloft conning station. The bridge wing consoles are mechanically linked to the pilot house console by pull pull cables. The main control console maintains operational override authority over all other operating stations (Fig. 8). The monitoring section using a hybrid computer system continuously surveys the propulsion system data points. Individual signals are compared in the memory bank against stored limits. If an alarm condition exists, an audible alarm is sounded, and the alarm is visually indicated on the propulsion mimic panel. Alarm acknowledgment silences the audible alarm, and the mimic alarm light switches from flashing to steady. When the alarm is corrected, the mimic light is extinguished. The monitor mimic is divided into three separate panels, one for each shaft system. The mimic panels use the darkboard concept to minimize operator error during emergencies. The mimic remains dark, except when an alarm condition exists. Each mimic panel also has a digital display counter that allows the operator to select individual data points for display. 7

8 Fig. 9 Typical FT4 marine power pac For record purposes, the monitor section includes a data logger which automatically prints out periodic log readings, equipment status changes, and alarm conditions and correction. Local control panels are provided at each prime mover. However, local-remote function transfer is controlled by the main control console. The ship's service system, consisting of three 750-kw diesel generator sets and distribution switchboards, has incorporated standard components with a high degree of commonality with those of the main propulsion diesel electric system. The eight-cylinder S.S. diesels are the same engine model as the propulsion units with about 80 percent interchangeability of parts. By standardization, such as common cylinder size, a significant reduction in spare parts inventory, special tool and training requirements has been accomplished. PROPULSION BOOST PLANT The boost plant of three FT4A-12 gas turbines driving the CRP propellers through marine reduction gears is used during heavy ice conditions. This operating mode has a normal rating of 20,000 shp with a continuous overlaod capability of 25,000 shp per shaft. The boost plant will power the icebreaker through a maximum ice thickness of 6 ft at a continuous speed or advance of 3 knots, and up to 21 ft of ice depth by ramming. The gas turbine boost plant does not possess flexibility of shaft system crossover capability, Fig. 10 Lifting FT4 marine power pac aboard a vessel under construction as does the diesel electric base load plant. However, critical system components and auxiliary equipment, such as reduction gear clutches and various system pumps, have been duplicated to ensure high system reliability. In keeping with vessel and propulsion design concepts, the FT4 Marine Power Pac is a self-contained module including engine subbase and acoustic/thermal enclosure, with all subsystems prepiped and prewired to interface connections at the engine subbase for minimum shipyard interface Since the modularization of the Marine Power Pac has been discussed in detail in other publications', 2 only significant design changes for the icebreaker will be covered. Ice strengthening of the hull structure has restricted the available overhead space for gas turbine maintenance removal. Therefore, the engine enclosure has been designed for engine removal through large access doors into the gas turbine inlet plenum. Actual lifting and movement of the engine from the enclosure to the inlet plenum is accomplished by overhead handling tools carried by trolleys built into the enclosure roof and supported by the enclosure structure. 1 McAllister, P. J., "Modularization and Installation of the Gas Turbine Propulsion Syster in Euroliner," American Society of Mechanical Engineers, San Francisco, Calif., March O'Neil, D. A., Carpenter, D. D., and Holburn, J. G., "System Integration of the GTS Euroliner from Conception to Operation," Society of Naval Architects and Marine Engineers, New Yor Metropolitan Section, Sept

9 PRECIPITATOR TEMPERATURE REGULATING VALVE OIL FLOW - BREATHER FLOW Fig. 11 Block diagram FT4 single lube oil system A single lube oil system has been incorporated to combine the normally separate gas generator and free turbine lube oil systems reducing shipboard maintenance and spare parts requirements (Fig. 11). Automatically closing louvers are incorporated in the gas turbine enclosure cooling air inlets and exhausts. The louvers serve a dual purpose by preventing cold starts from arctic airflow when the engines are shut down, and prevent airflow to the enclosure in case of fire. The gas turbines are located in separate machinery spaces from the reduction gears with the gas turbine high-speed shafting passing through a common bulkhead. Due to a structural ice belt in the way of the FT4 and reduction gear, the original configuration extended the high-speed shafting between these units with a 3-ft spool shaft and pedestal bearing in order to maintain equipment clearance. A lateral shaft analysis of the spool shaft arrangement revealed several critical speeds within the operating range of the system. Direct coupling of the gas turbine output shaft through a flexible coupling to the gear input flange was deemed the optimum solution. In order to move the turbine aft 3 ft without interference with the ship's structure, it was necessary to utilize a non-standard exhaust elbow. The rectangular exhaust elbow, replacing the standard rounded exhaust elbow, reduces overall gas turbine envelope approximately 3 ft and will be incorporated in the icebreaker. The aerodynamic design of the rectangular exhaust elbow has been model tested and confirmed as a component of the icebreaker exhaust ducting. Fig. 12 Reduction gear schematic Inlet duct model tests have also been completed verifying the compatibility of the ship's ducting design. In order to maintain watertight integrity between the gas turbine room and the reduction gear room of the icebreaker, a gas turbine shaft seal is mounted on the reduction gear side of the bulkhead. The shaft seal is a static one, sealing only when the shaft is at rest. Operation of the seal is interlocked to prevent seal engagement when the gas turbine is operating or starting the gas turbine with the seal engaged. The FT4 is directly coupled to the reduction gear by a flexible, dry diaphragm coupling. The 20,000-shp, 175-rpm reduction gears are locked train, double reduction marine gears. A dental tooth type shaft disconnect coupling engages the gearbox to the line shafting. The gear trains are designed to withstand torque loadings of 200 percent during ship's lowspeed icebreaking and 250 percent torque (50,000 shp) for 1-sec cycles. The "K" factors are conservatively rated at 90 in the first reduction gear train and 80 in the low-speed train. Gas turbine input is transmitted directly to the high-speed gears. Utilizing a quill shaft arrangement, a dry, friction clutch is located on each low-speed pinion. For system reliability, each clutch is capable of transmitting full rated torque, or 200 percent full power torque (Fig. 12). The low-speed clutch and main shaft disconnect coupling arrangement permits maximum system flexibility. The shaft disconnect coupling will normally be disengaged during diesel electric operation. However, during icebreaking, the coupling may be engaged which results in only the low-speed gear set turning over. In the latter 9

10 25 ri2 20 ' o - 5 r <1;\:=." FREE ROUTE ^cei brakes are incorporated in the line shafting to be operational in all propulsion modes. The controllable pitch propellers, the first application of a CRP in a polar icebreaker, are designed in accordance with "Det Norske Veritas" rules for icebreakers. The four-bladed propellers provide maximum thrust in an icebreaking condition of 175 rpm and 20,000 shp with a ship speed of 3 knots, and maximum efficiency will be at 110 rpm, and 3000 shp with a ship speed of 16 knots fill M 1 zii I I I LEVER POSITION 5 ce Fig. 13 Typical propeller pitch schedule condition, transfer from diesel electric to gas turbine operation in heavy ice conditions does not necessitate stopping the shaft to engage the gas turbine drive train to the propulsion shafting. The control of the gas turbine boost mode is maintained by the Main Propulsion Control System. Operational control and monitoring functions are integrated within the main control console in the same manner as the diesel-electric propulsion plant. The gas turbine utilizes an electronic fuel control for both speed and power governing. In normal operation, the gas turbine will be speed governed to maintain free turbine output shaft speed at 3600 rpm, which is equivalent to 175 srpm. Should the icebreaker encounter extreme ice conditions or experience ice milling, either condition causing an underspeed condition with reduced propeller pitch at 20,000 shp, the gas generator will be automatically switched to power governing. Gas generator power output will be increased on a preset schedule to a maximum output of 25,000 shp. In the power governing mode, a topping limit protects the system from overspeeding. In the event the free turbine becomes unloaded and accelerates to 3850 rpm, a redundant overspeed protection system automatically shuts down the gas generator. The propulsion shaft system is protected from an overtorque condition exceeding two times rated capacity or 40,000 shp. Electronic fuel control logic compares free turbine speed, gas generator speed and inlet air temperature against programmed values, and limits gas generator output when programmed values are exceeded. External shaft thrust bearings and shaft MODE TRANSFER Transfer in the propulsion mode of operation involves a detail sequence of events, the majority of which are either interlocked or sequenced to prevent operator error. Starting in one diesel generator per shaft mode, a brief description of major transfer points follows: At the propulsion set-up board using the electrical mimic, the operator will select the desired diesel generator to motor combination. With the generator set-up switch closed, the diesel unit is started and idled at 400 rpm for warm-up. Having selected the appropriate generator and motor exciter-regulators,, the diesel is switched to 900 rpm. At speed, the exciter-regulator is energized and the operator has full control at the shaft throttle lever. Unless the generator set-up switch had been set up before initial start-up for two-unit operation, all changes in number of units or in the onthe-line diesel generator unit must be accomplished at no load. Assuming the system was set for single diesel generator operation, the second diesel generator set would be started at 400 rpm and warmed up. When the second unit is ready, the on-the-line unit is unloaded and the generator field is brought to zero by the "residual field killer" circuit. When the set-up switch indicates zero potential in the contacts, the set-up switch is reset for the new generator motor combination. The switch is interlocked to prevent opening or closing with a potential to prevent arcing of the contacts. With the set-up switch reset, the generator fields are energized at 900 rpm, and the operator again maintains full propulsion control at the throttle lever in the two diesel generator per shaft mode. All mode transfers from diesel electric to gas turbine or vice versa are at a propeller speed of 105 rpm and neutral pitch with diesel electric speed control and gas turbine at idle power. This rpm is approximately 80 percent maximum diesel electric operating speed and 00 percent of gas turbine maximum operating speed. Prior to any transfer from diesel electric to gas turbine, the 10

11 propulsion shaft disconnect coupling must have been engaged with the propulsion shafting stopped. If the shaft must be stopped to engage the coupling, transfer should be made at that point. However, in ice fields, it is desirable to keep the propulsion shafting turning to minimize propeller damage; therefore, so-called "on the fly" transfer with the shaft coupling engaged is required. After the gas turbines have been started, a mode select switch is placed in a transfer position which commands 105 rpm and neutral pitch. The turbine clutches are engaged on operator command. With the turbine clutches in, the generator field is brought to zero and the diesels switched to 400 rpm. The motor field is switched off and the motor brushes are raised from the propulsion set-up board. The mode select switch is placed in the gas turbine position. The turbine will automatically drive to 175 rpm provided the motor brushes have been lifted and other permissives met. The transfer at this point is complete and the operator has full control at the shaft throttle lever. Transfer from gas turbine to diesel generator is accomplished by reversing the procedure. ANALYSIS AND TESTS New ship design requires extensive testing and analyses of the machinery systems as well as hull design. Properly conducted analyses can verify design or identify potential problem areas so that design concepts can incorporate necessary requirements. Extensive analyses and testing has been completed or is continuing to confirm individual component and propulsion system design. The two most important analyses for the propulsion machinery design and operation are the system Torsional Analysis and system Transient Analysis or Simulation. The completed torsional analysis has revealed system critical speeds within the different modes of operation. Mechanical design changes to minimize the effect of the critical speeds was precluded by the space and time limitations of the vessel. Therefore, automatic propulsion system speed and power modulation by the control system is being investigated. The control system has been programmed to minimize loading while passing through critical speeds and to prevent continual system operation at the critical speeds. The investigation of the system operation and response at the critical speeds is being conducted as an area of the propulsion transient analysis. The transient analysis, using a digital Fig. 14 Inlet model testing with simulated superstructure for 100-mph crosswinds model, will demonstrate transient responses to various operations and conditions. The program has the versatility to simulate dynamic and steady-state performance which reflects the cumulative response of all components. The input data includes characteristics of the hull, machinery, propeller, and control components. The results of the simulation model will be used in the refinement and selection of the main propulsion control system components. Individual machinery analysis has included a torsional analysis of the diesel generator sets. The analysis has indicated the sets are free of torsional criticals imposing stresses greater than 4 percent of the tensile strength of the system throughout the operating range. The analysis will be verified by a torsiograph of the first production unit. Gas turbine inlet and exhaust duct arrangement model testing has been completed. The tests, which duplicated ambient conditions of up to 100- mph wind speeds, have proved the acceptability of the final duct design. Duct pressure losses were determined to be 3.5 in. of water in the inlet and 1.5 in. of water in the exhaust ducting at the ambient conditions of a standard day and maximum wind velocity of 25 knots (Fig. 14). Hull and propeller model testing results completed by other responsible activities have been incorporated into the digital simulation model as noted. Performance testing of propulsion equipment will be accomplished at each manufacturer's facility. 11

12 SUMMARY The equipment discussed in this paper is currently being fabricated. At the time of presentation, the majority of equipment will be constructed and performance testing completed in preparation for installation into the vessel. All design efforts have been exerted within specification requirements to formulate and integrate subsystems containing many components into a cohesive and viable propulsion system. The objective of the design has been to provide POLAR STAR, WAGB-10, the operational flexibility and reliability to meet its envisioned mission. The final analysis, of course, will be the vessel's acceptance trials and service deployment. 12