What is the purpose of the inner guard ring in ARPA?

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Multiple Choice

What is the purpose of the inner guard ring in ARPA?

The inner guard ring provides a visual alert that a target is approaching the pre-set Closest Point of Approach. On an ARPA display, this ring marks the boundary of the defined collision-risk area. When a target’s predicted path would bring it inside that ring (i.e., the CPA would be at or below the set limit), ARPA flags it and an alert is generated for the watch officer. This helps you quickly identify vessels that require action without doing manual CPA calculations. It isn’t about relative speed, night operation, or bearing to aids; it’s a boundary cue for potential collision risk.

The inner guard ring provides a visual alert that a target is approaching the pre-set Closest Point of Approach. On an ARPA display, this ring marks the boundary of the defined collision-risk area. When a target’s predicted path would bring it inside that ring (i.e., the CPA would be at or below the set limit), ARPA flags it and an alert is generated for the watch officer. This helps you quickly identify vessels that require action without doing manual CPA calculations. It isn’t about relative speed, night operation, or bearing to aids; it’s a boundary cue for potential collision risk.

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