Failure to Engage There are several problems that can cause a brake to fail to engage. You must understand the operating principles associated with the system. First, check to see if there is sufficient air or oil pressure for operation. It is pretty obvious that if the activating medium (air or oil) is missing, this condition should produce an alarm at the console.

Once you determine that the activating medium is available, you should try the manual control. If the manual control works, you should consider an electrical fault as the problem source. If the manual control does not work, you should continue troubleshooting. If the pressure regulator is not working, the supply cutout valve (if installed) may be closed, or there may be a blockage or leak in the supply line. These are all possible causes for the failure. The last possibility to check is the electrical control. Did the brake actually engage? If the brake engages, but you do not receive a brake engaged indication, just look at the PT speed to verify a slowing down or a stop. If the PT has stopped, your indicator light may be out or the indicator switch may be bad. If the PT does not stop, you may need help locating where the command signal is lost.

Failure to Release When a brake fails to release, the three most common causes are a command problem, a bad position indicator switch, or a bad indicator light. If none of these are the cause, you should check for a binding caliper and weak or damaged return springs.

Failure to Stop Rotation When the brake applies but does not stop rotation, the most common causes are insufficient actuating pressure, contaminated brake pads, a damaged rotor (disc), or a binding caliper piston.

ALIGNMENTS AND ADJUSTMENTS Basically, the only components that have any adjustments or alignment checks are the PT and shaft brake systems. Normally, all of these adjustments or alignments are performed as requirements resulting from a PMS inspection.

REMOVAL AND REPLACEMENT OF COMPONENTS The removal and replacement of a clutch maybe performed by your ship's personnel if there is sufficient time or if a casualty occurs. Most of the time, however, the engineer officer will opt to have an outside activity perform the work.

On the other hand, the brakes and their subsystems can be easily maintained by your ship's maintenance technicians and personnel.

LINE SHAFT (SPRING) BEARINGS The line shaft (spring) bearings are self-aligning, oil-lubricated journal bearings. Each bearing is a self-contained assembly with its own oil reservoir that contains 2190 TEP oil.

An oil disc (ring) clamped to the shaft is used in each bearing to deliver oil to the upper bearing and journal surfaces. As the disc rotates, it picks up oil from the bearing reservoir and carries it to the oil scraper on the upper shell. The scraper removes oil from the disc and directs it to the upper bearing lining. A clear sight cover on the bearing housing allows visual confirmation of the oil disc operation. Figure 3-7 shows a typical disc-oiled line shaft bearing.

All bearing pedestals have an oil level rod and an oil reservoir thermometer for checking oil level and temperature. A resistance temperature detector (RTD) is installed in the lower bearing shell of each oil-lubricated bearing. The RTDs provide for remote readouts of each bearing's temperature on the digital demand displays.

Clearances are taken with a depth micrometer through a port in the upper bearing housing, which contains the anti-rotation pin. The original installation readings are stamped into the flat surface adjacent to this port. You must take readings according to PMS requirements or when an abnormal condition exists.

For information on maximum wear limits and repair procedures, you should consult the appropriate manufacturer's technical manual and NSTM, chapter 244, "Shafting, Bearings, and Seals."

STRUT AND STERN TUBE BEARINGS Each propeller shaft extending aft of the stern tube is supported by two struts, each containing a seawater-cooled bearing. Figure 3-8 shows a typical strut bearing.

Stern tube bearings are in constant contact with the seawater surrounding the stern tubes. The clean seawater that passes through the stem tube seals from the ship's seawater service system or firemain system (in emergencies) also flows through the stern tube bearings. Stern tube bearings are identical to forward strut bearings. However, aft strut bearings are roughly 5 inches larger in diameter and twice as long as stem tube bearings. Remember that stem tube bearings are not remotely monitored.

PROPULSION SYSTEMS The ship's propulsion thrust is provided by hydraulically actuated propellers. In the Gas Turbine Systems Technician (Electrical) 3/ Gas Turbine Systems Technician (Mechanical) 3, volume 1, NAVEDTRA 10563, you were provided with a complete description of propulsion systems and how they operate. As a gas turbine supervisor you need to be knowledgeable and experienced with a variety of gas turbine propulsion

Figure 3-7.- Disc-oiled line shaft bearing,

Figure 3- 8.- Details of a typical underwater strut bearing. system operations. This proficiency combined with local manual operating mode. The maximum rate of leadership skills will assist you daily in your supervisory role.