GYRO REPEATER SYSTEMS
Most modern vessels carry two master gyros providing backup should one of the units fail. Output from the two master units goes to a selector switch which can be operated by the deck officer to select between units. Normally, the master units are switched over daily to ensure that the repeater system works correctly on either master gyro.
From the selector switch or, if the system has a single master gyro, the transmitter, signals go to the transmission amplifier/distribution control. This unit has each repeater on a separate circuit, is normally switched and fused, and provides sufficient power to drive all the vessel's repeaters. Repeaters are located not only in bearing or steering units near or on the vessel's bridge, but also in radars, radio direction finders, automatic steering systems, course recorders, and other similar units. The distribution system also provides input to radionavigation equipment requiring course data information.
There are two common types of repeater systems. The first is the step system, which produces segmented signals driving a repeater motor in three separate "steps." This system is generally associated with the older type of gyro systems. The second is the newer synchro system. This uses a different voltage requirement from the step system with a synchro style operating motor. The movement ofthis type repeater is truer to, the movement of the master compass.
The actual repeaters are found in various forms, including the standard repeater, which exhibits the entire azimuth ring, or the open scale repeater, which shows a larger, but only partial, section of the azimuth ring. The open scale repeater is most commonly used as a steering repeater. Signals from the repeater system can also be utilized to provide other types of heading information such as digital readouts used in radars or radionavigation receivers and graphic displays used in course recorders.
There are two familiar types of course recorders. The older style utilizes an eight-day wind-up clock mechanism with two ink pens, one showing the compass quadrant and the other showing the course. The newer type uses an electrically driven clock mechanism with two electric styluses. This graph mechanism works similarly to the fathometer in that special graph paper is drawn over a metal desk and an electrical signal scores the graph paper to show the quadrant and course.
There are several important points that the watch stander should keep in mind when using the gyro system:
1. Ensure that all repeaters are aligned with the master gyro and if there is a dual gyro system aboard, ensure that any difference in their readings is constantly noted.
2. Azimuths for determining compass error should be taken as frequently as permissible, and the information applied to both master compasses if a dual gyro system is installed.
3. All master gyros are equipped with speed and latitude correctors.
These are necessary because the directive force of the gyro decreases as you get nearer the poles. There is also an error introduced in the master gyro by the vessel's motion along its track. Each master gyro has specific parameters for setting these correctors, but generally they should be kept within 3 degrees oflatitude and 3 knots of speed.
4. When switching from one gyro system to another be sure your repeaters are lined up with the master gyro you are switching to before changing over. Be sure to inspect all equipment frequently. Every system has a manual that details maintenance responsibilities for the unit. Be sure to follow these maintenance plans as required.
5. Errors in the gyro system can be introduced by a ship's fluctuating power supply. The gyro system should be on emergency circuits. If extensive variations in the power source are noted be sure to inform the vessel's engineer so that it may be corrected as soon as possible.
6. Although most manufacturers recommend starting a gyro within only a few hours of use, the prudent operator will bring the system on line in order to provide as much time as possible for problems to become noticeable. The gyro will hunt or oscillate prior to settling out so the gyro should be started as close to the vessel's heading as possible to minimize this settling time. If the vessel is located at the dock, you can get the vessel's heading from a chart. Be sure to set the speed corrector at zero when tied up. Starting the gyro at sea should also be done as close to the heading as possible with the speed corrector set accordingly. Remember that the axis of the rotor aligns itself with the geographic meridian and the gyro is not necessarily north seeking. If you start the gyro up 90 degrees or more from the vessel's heading, your gyro may have a l80-degree error. Every gyro has a specified start-up and shut-down procedure which should be followed. This information is available in the unit's operating manual.
7. Small constant errors in a gyro may be removed by moving the master compass lubber line or shifting the binnacle housing, depending on the style ofthe unit.
8. Be sure to remove the gyro's locking latches or uncage the unit and set its controls in the proper operating mode.
9. Each gyro system has a failure alarm connected with it.
