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Radar ARPA Automatic Radar Plotting Aid Explained by City Sailing
11 February 2026 · 13 min · 623 views · Dover Harbour
Ferry Gotland alters course to dock at harbor
What this video covers
Paul from City Sailing demonstrates ARPA (Automatic Radar Plotting Aid) in real traffic at Dover Harbour, using a live radar display cross-referenced with Actis to track multiple moving targets simultaneously.▶ 0:00 The radar is tuned at 12 miles, then stepped down to 1.5 miles on short pulse for better close-in definition, with the display set to North-up and stabilized.▶ 0:02 ARPA vector time is set to six minutes, then adjusted to two minutes and one minute to show where each target will be at those intervals.▶ 3:22 CPA and TCPA limits are zeroed for the demonstration to suppress alarms; Paul explains they should be set higher offshore.▶ 1:31 He distinguishes true vectors (red, showing absolute movement) from relative vectors (white/green, showing movement relative to own vessel) and stresses that relative mode is correct for collision avoidance under Rule 19.▶ 4:04 Targets include the USS Eagle, two cross-Channel ferries, a hovercraft, a square rigger, and inbound cargo ships doing 17–19 knots, with one showing CPA zero and TCPA 4.3 minutes.▶ 9:00 Paul recommends practicing ARPA first in good visibility so targets can be visually confirmed, then repeating the exercise at night and in fog.▶ 11:15
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