Advanced Scenario Check: Heading Conflict and Two-Contact Action

At 0952 in this fictional exercise, heavy rain has reduced visibility below the next visual pilotage range. Contact A has closed from 2.4 NM to 1.2 NM in twelve minutes on a nearly steady relative bearing while own heading and speed were steady. Contact B is 0.9 NM away at relative bearing 120°, abaft the starboard beam. A sound signal is heard apparently forward.

The automatic display shows contact A passing at 0.7 NM, but the radar heading input differs from the steering compass by 8° and the target was reacquired fifty seconds ago. MCA guidance says incorrect heading or speed inputs can cause serious output errors and automatic plots can require up to about three minutes for full smoothed accuracy. The displayed CPA and true vectors are therefore not release evidence.

The raw calculation gives 6 kn average relative closure and twelve minutes to nominal zero range if nothing changed. That does not calculate CPA or target course, but it defeats any argument for holding passage speed while waiting for the display. Because the sound signal is apparently forward and risk has not been determined not to exist, command the Rule 19 speed-and-caution response now: minimum speed to keep course, all way off if necessary and extreme caution, with engines ready, lights, signal and lookout maintained.

Do not convert the rule's alteration cautions into an unsupported turn. Port is to be avoided so far as possible for a vessel forward of the beam; turning towards a vessel abeam or abaft the beam is also to be avoided so far as possible. Contact B therefore makes an automatic starboard alteration unsafe to assume, while contact A makes an automatic port alteration unsafe to assume. The exercise has not provided a trustworthy plot or sea-room case for either turn.

Assign one person to helm and engine response, one to sight-and-hearing lookout, one to radar observations and input checks, and one to navigation and sea room where crew permit. Record both contacts separately, correct or isolate the suspect heading input, use suitable radar ranges and settings, and set the next timed observation. AIS may help association but cannot replace the radar trend or the Rules; an uncertain VHF negotiation is not the solution.

When repeated observations and the navigation picture support effective further action, make it positive, early enough and large enough to be apparent, then check the result until both contacts are finally past and clear. This written scenario deliberately stops short of inventing a universal course alteration. A real decision requires the complete current plot, sea room, vessel response and competent practical operation.