Navigation General · ARPA
On an ARPA display set to TRUE MOTION mode, own ship's echo:
- ARemains at the center of the display and all other targets move relative to it
- BMoves across the display at its actual course and speed, and the display resets periodically✓ Correct
- CIs suppressed so only target vessels are displayed
- DMoves only when own ship changes course; speed changes are not reflected
Explanation
In true-motion mode, own ship's echo moves across the PPI screen at the vessel's actual course and speed (using gyro and log inputs), just as targets move at their own true velocities. The display resets when own ship approaches the screen edge. This mode makes it easier to visualize the true tracks of all vessels but requires accurate speed and heading input.
Authority: Radar Navigation Manual (Pub. 1310), Ch. 5
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