Which ARPA data should you use in order to determine if a close quarters situation will develop with a target vessel?

To determine if a close quarters situation will develop with a target vessel, using relative track information is essential. This data provides insights into the target vessel's course and speed relative to your own vessel. By analyzing the relative motion, you can assess whether the vessels are on a collision course or if they are likely to pass safely.

Relative track information allows navigators to visualize the target's predicted path, including any changes in trajectory that may occur. Understanding this relative motion is critical in making timely decisions about course alterations or speed adjustments to ensure safe navigation and avoid potential collisions.

While other data points like the set and drift of the current, predicted time of closest point of approach (CPA), and initial range can provide useful information, they do not give as direct an indication of the dynamics between your vessel and a target as relative track information does. Each of these other elements contributes to situational awareness, but it is the relative track that directly informs you about the impending interaction between vessels.