Your ARPA has two guard zones. What is the purpose of the inner guard zone?

The inner guard zone in an Automatic Radar Plotting Aid (ARPA) system serves as a critical area for monitoring smaller targets that can be detected at distances closer than those monitored by the outer guard zone. Its primary purpose is to enhance situational awareness by ensuring that any small vessels or potential hazards entering this inner space trigger an alert, allowing the watch officer to respond quickly.

By focusing on targets that are initially detected within this closer range, the inner guard zone helps in identifying potential collisions or navigational hazards that could be missed if only relying on the broader outer zone. This is especially important in busy maritime traffic conditions where small vessels can easily change courses or be obscured by larger vessels.

In contrast, the other options suggest different functionalities that do not accurately reflect the primary role of the inner guard zone. For example, the purpose of notifying about a preset CPA limit relates more to trajectory calculations than to direct detection of targets. Similarly, while guarding against target loss during critical maneuvers is vital, the inner guard zone specifically emphasizes early detection within its designated area, rather than addressing broader operational strategies. Thus, understanding the specific role of the inner guard zone reinforces the importance of proactive monitoring in maintaining safety in navigation.