Management-level passage planning, independent evidence and collision risk
A master-level navigation decision combines passage planning, position evidence, vessel capability and the applicable collision rules. An accurate-looking electronic symbol does not prove that its underlying sensor, chart information or interpretation is correct. Plan for the actual route and continually reassess the evidence during execution.
Appraise, plan, execute and monitor
Identify the actual charts, warnings, weather, tides, traffic arrangements, pilotage and vessel limitations. Keep horizontal position datum and vertical height or sounding datum distinct. A bridge-clearance calculation and an under-keel-clearance calculation use different reference levels. Include the actual vessel condition and relevant allowances rather than convert one classroom depth sum into permission to enter.
A great-circle route minimizes distance on the spherical model but can introduce latitude, weather or ice constraints. A rhumb line has a constant bearing; that feature does not make it the safest or shortest route in every case. Select and monitor the appropriate track using the actual operational constraints.
Use independent position and motion evidence
GNSS information can be degraded, jammed or spoofed. Compare its indications with suitable independent radar, visual, dead-reckoning or other evidence. A repeated position from two screens sharing one receiver is not independent confirmation. Investigate an unexplained change before accepting the new apparent position.
Parallel indexing monitors cross-track relationships to suitable fixed radar targets. A radar range or visual bearing also carries measurement and identification uncertainty. A three-bearing cocked hat is not automatically resolved by choosing its geometric center. Use the available error evidence and the safest defensible assessment.
Speed through water and speed over ground represent different reference frames. Distinguish target relative motion, ground track, water-relative movement and actual heading. A ground vector must not be mistaken for a vessel's heading or its visual aspect. Trial maneuvering predicts the effect of supplied assumptions; it cannot guarantee that another vessel will hold course and speed.
Apply the rules to the actual encounter
Maintain a proper lookout, safe speed and systematic collision-risk assessment. Distinguish vessels in sight from radar-only encounters in restricted visibility. A fishing or sailing label does not create unconditional priority in a narrow channel, traffic scheme or overtaking situation.
Take appropriate positive action in ample time and monitor its effectiveness. A radio agreement is not a substitute for correct identification and the applicable rules. A stand-on role does not justify remaining inactive until a collision occurs. Bridge-team communication, the actual pilot exchange and timely escalation to the master support the decision, while practical shiphandling still depends on the real vessel and conditions.