Constant-Bearing Target in Fog Approaching a Traffic Lane Boundary
MV Endeavour Star, a 22,000 GT bulk carrier, is making 15 knots south-west-bound in the Dover Strait traffic separation scheme. Visibility has fallen to 0.3 nm in fog. The X-band radar (6 nm scale, north-up, relative motion) shows a target on the starboard bow bearing 038°R, range 5.6 nm, closing at 0.42 nm per minute. The ARPA predicts a CPA of 0.2 nm in 11 minutes, and the target's aspect suggests a fast ferry crossing from the Varne Bank area toward the French coast. The target answers neither VHF Ch 16 nor Ch 13, and AIS gives no name. Your ship is also being overtaken by a 12-knot car carrier now 1.1 nm on the port quarter. Engines are on bridge control and the ship is fully manoeuvrable. The master has just arrived on the bridge. There is a north-going traffic lane 1.5 nm to port beyond the separation zone.
1. Identify which COLREGs rule governs each of the two relationships, and state whether risk of collision exists. Give the radar and ARPA evidence you would rely on and its limitations.
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Crossing ferry, 038°R at 5.6 nm. The ships are not in sight of one another, so the steering and sailing rules of Part B, Section II (Rules 11–18) do not apply. Rule 19 (conduct of vessels in restricted visibility) governs, even though the geometry looks like a Rule 15 crossing. Risk of collision exists on the ARPA evidence: a steady relative bearing, range closing at 0.42 nm/min and a predicted CPA of 0.2 nm mean the vessels would pass within a few hundred metres. Rule 7(d) requires that assumptions not be based on scanty information, so I would confirm with: a second plot three minutes later, switching to true-motion/true vectors, checking the target's aspect against its relative track, and using both X and S band if fitted.
Limits of the evidence. At 0.3 nm visibility the target may be a small, slow or barely-radar-reflective craft mis-sized by the ARPA; the ferry may be altering speed for the lane; and a 0.2 nm CPA is inside my own ship's turning circle and stopping distance, so it is not a safe passing distance in fog.
Overtaking car carrier, 1.1 nm on the port quarter. Rule 19 applies here too; the risk is a vessel coming up from astern while I manoeuvre. It is a material constraint on my freedom to turn to port.
2. State the manoeuvre you would execute in the next few minutes, with reasons for direction and magnitude, and the check you would make afterwards.
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Direction. I would turn to starboard. Rule 19(d)(i) forbids an alteration to port for a vessel forward of the beam unless another vessel is involved in the risk, and here a second vessel is closing from the port quarter, so a port turn would both open the crossing and close the overtaking risk. A starboard turn also lets the ferry pass ahead, matching the geometry that would apply in sight (Rule 15/16) and reducing the chance of confusing the ferry's bridge team.
Magnitude. The alteration must be large enough to be obvious on the other vessel's radar - at least 30–40°, not a series of small nudges. Small alterations are exactly what Rule 19(d)(ii) warns against, because the other vessel cannot infer a new aspect from them. I would order "starboard 40" and log the time, and simultaneously reduce to harbour/half speed: Rule 19(e) requires reducing to the minimum speed at which the ship can be kept on course once a close-quarters situation is developing, and speed reduction buys plotting time and shortens stopping distance.
The check. After steadying on the new course I would re-plot: the target's bearing should draw steadily aft to starboard; if the relative bearing remains constant, the alteration was insufficient and I must stop or take further bold action. I would also confirm the overtaking vessel's CPA has not deteriorated and hand over a clear conning instruction to the officer of the watch before the ferry emerges from the fog.
3. List the records, notifications and speed/sounding considerations you would want before and during the passage of the fog bank.
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Sound signals and speed. Rule 19(b) requires proceeding at a safe speed for the prevailing circumstances; Rule 35 requires one prolonged blast at intervals of not more than two minutes for a power-driven vessel making way, and two prolonged blasts with a one-second interval when stopped. I would ensure the whistle is on automatic and that the officer of the watch reports every fog signal heard forward of the beam, which triggers Rule 19(e).
Records. Bridge bell book and movement book entries for each alteration, the ARPA plot history, radar log/performance check, engine movement log, names of persons on the bridge, and the times fog signals were heard. A contemporaneous track of the decision sequence is what protects the master later.
Notifications. Notify Dover Coastguard/VTS by VHF with position, course, speed and intentions; broadcast a security call on Ch 16/13 warning other traffic of a vessel manoeuvring in fog in the lane; and inform the company/DPA if the ship is delayed or the situation escalates. Any VHF attempt to the ferry, even unanswered, should be logged.
Sounding and readiness. Switch soundings, keep the echo sounder running, reduce to manoeuvring speed for the engine room, confirm steering gear on the second pump where fitted, and close up the bridge with both lookouts posted forward where they can be heard. Consider leaving the lane if safe passage can no longer be assured.