CRP/ CPP SYSTEMS OPERATIONS In this section, we will briefly cover routine and emergency operations of the CRP/ CPP systems. Since the various ship systems are functionally the same, we will not indicate ship type except when necessary. However, if you need to review the basic design and operational characteristics of these systems, consult GSE3/ GSM3, volumes 1 and 2.

Routine Operation Propeller pitch changes can be made through the full range of travel in one continuous movement. The pitch change can be made in automatic, remote manual, or pitch change, 30 seconds from full ahead to full astern, is determined by the response of the hydraulic system. Pitch change rate is NOT determined by the speed of movement of the control lever.

The CRP/ CPP systems were designed to maximize the ability of the ship's propulsion GTE to accelerate and decelerate rapidly and to enhance maneuverability. To further enhance the systems' performance and to make them more "user friendly," some subtle changes were made. These changes have been installed on the newest gas turbine ship platform, the DDG-51 class ship. The following sections will explain some of these changes and the contributions they make to system performance.

As a GS supervisor, you should be aware of the changes incorporated in the CRP/ CPP systems installed on the DDG-51 class ships and the advantages they offer in the performance and operation of these systems. Look at some of the components that have changed in the OD box and the pitch indicating system.

OIL DISTRIBUTION BOX.- On DD-51 class ships, the configuration of the OD box has undergone several changes. The emergency pitch pump hose connections have been moved from the bottom of the OD box to the low-pressure chamber cover, as shown in

PITCH INDICATING SYSTEM.- A significant change was made to the pitch indicating system. There are now two types of pitch indicating systems installed on DDG-51 class ships. One system is temperature compensated while the other is electronic. Because these two systems operate independently, DDG-51 class ships have both a normal and alternate means of measuring propeller pitch.

figure 3-9. This change makes it easier for the operator Temperature-Compensated Pitch Indicator to make the connections during testing or in case of an System. - On DDG-51 class ships , t he emergency. temperature-compensated pitch scale platform is rigidly

Figure 3-9.- Emergency pitch arrangement.

connected to the OD box. The scale platform holds the feedback potentiometer and local pitch indicator, as shown in views A and B of figure 3-10. This indicator is defined as temperature compensated because the indicator arm is connected to the prairie air tube. Look at view B. The prairie air tube is normally pressurized with air at a controlled temperature, and will have a fixed amount of thermal growth. Hence, the indicator arm is

provided with a thermally stable (temperature-compensated) surface, a primary means to sense and indicate propeller pitch, and a means to relay that information to the machinery control system (MCS).

Electronic Pitch Indicator System.- In addition to the temperature-compensated pitch indicator installed on the OD box of DDG-51 class ships, an electronic pitch position transducer is installed behind a

Figure 3-10.- Pitch scale platform showing temperature-compensated pitch indicating system.

cover plate on the propeller hub. This arrangement is The electronic pitch indicator system also contains shown in view A of figure 3-11. The electronic pitch a stationary electronics cabinet, rotary transformer, and indicator receives an input from a sensor assembly rotating electronics cylinder. The stationary electronics mounted inside the propeller hub, as shown in detail in cabinet is mounted adjacent to the OD box. It contains the circuitry to provide a 10-kHz excitation signal to, view B of figure 3-11. The sensor (wand) extends from the small electronics package (handle) located in the hub and receive a propeller pitch position feedback signal from, the rotary transformer. The cabinet also has two cone and cover into an axial hole drilled into the piston light emitting diode (LED) displays that show propeller rod. The hole contains a magnetic ring that allows the pitch in both feet and percent of design ahead and astern sensor to measure propeller pitch position. pitch. The rotary transformer contains both the

Figure 3-11.- Hub-mounted electronic pitch position transducer.

transducer excitation and output coils. The rotating electronics cylinder rectifies the rotary transformer excitation to 24 V dc for powering the hub-mounted transducer and receives the transducer output. The rotating electronics cylinder is attached to the prairie air tube extension at the end of the OD box. The cylinder electronically regulates the transducer output to -3 kHz for the rotary transformer. For a more detailed description of this system's operation, consult the DDG-51 propulsion plant manual or the DDG-51 CPP system technical manual.