Electronic Chart Display and Information Systems (ECDIS) and Automatic Radar Plotting Aids (ARPA) constitute the primary operational core of integrated bridge systems. However, effective watchkeeping relies not on passive monitoring of digital screens, but on the systematic verification of sensor data against external navigational realities. The Officer of the Watch (OOW) must understand the fundamental principles, operational limitations, and sensor inputs governing both systems to prevent over-reliance and situational blindness.
“Navigation with ECDIS is fundamentally different from traditional paper chart navigation. Over-reliance on automated systems without active cross-checking and radar overlay comparison has been identified as a contributing factor in numerous groundings and close-quarters situations.”
— UK Maritime and Coastguard Agency (MCA), Marine Guidance Note MGN 379 (M+F) & IMO MSC.1/Circ.1503.
Safety Contour Configuration and Sensor Cross-Checking
Configuring appropriate safety contours, shallow contours, and depth alerts is a prerequisite before entering coastal or pilotage waters. Relying exclusively on GNSS-derived positions within ECDIS creates significant vulnerabilities to signal degradation or spoofing. Navigating officers must routinely employ independent verification methods, including radar overlay alignment, visual bearings, and parallel indexing techniques along planned tracks.
Radar Target Tracking (ARPA) and Vector Analysis
When assessing risk of collision under COLREG Rule 7, ARPA provides indispensable quantitative target data. Officers must distinguish between Relative Vectors (essential for immediate collision risk and Closest Point of Approach assessment) and True Vectors (crucial for evaluating targets’ actual aspect and heading). Pre-setting realistic CPA (Closest Point of Approach) and TCPA (Time to CPA) alarm thresholds ensures timely evasive action in strict accordance with COLREG Rule 8.
Key Takeaways for Bridge Watchkeepers
Manage Warning Overload: Acknowledge alarms only after identifying and addressing the underlying navigational trigger.
Active Lookout First: Electronic tools are decision-support aids; maintaining a proper lookout by sight and hearing remains non-negotiable under COLREG Rule 5.
Verify Dual Sensors: Never accept position fixes or collision assessments from a single sensor without corroborating radar ranges and visual data.
References:
- International Maritime Organization (IMO). Performance Standards for Electronic Chart Display and Information Systems (ECDIS), Resolution MSC.232(82).
- International Maritime Organization (IMO). International Regulations for Preventing Collisions at Sea, 1972 (COLREGs), Rules 5, 7, and 8.
- Nautical Institute. ECDIS and Positioning: A Guide to Good Practice, London.