In the Dover Strait TSS, visibility drops to 50m in very dense fog. Your vessel is a 180m tanker. Traffic is heavy. Should you stop and anchor? What factors govern this decision?

A. STOPPING IN A TSS IN DENSE FOG — factors and decision: RULE 10(h): a vessel shall not anchor in a TSS or in the area near its ends if it can avoid doing so. Therefore, anchoring in the Dover Strait TSS is strongly disfavoured and only permitted if unavoidable (engine failure, medical emergency). FACTORS GOVERNING PROCEED/STOP DECISION: (1) RULE 19 — safe speed: at 50m visibility, no ship of 180m length can stop within 50m. You literally cannot see enough to manoeuvre safely. Speed may need to be absolute minimum steerage — 2-3 knots; (2) TRAFFIC DENSITY: Dover Strait carries ~400-500 vessel transits per day — stopping (not anchoring) creates a hazard for overtaking vessels; (3) ANCHORING OPTION: if you have adequate sea room OUTSIDE the TSS (e.g., in the Downs anchorage east of the Strait) then anchoring is viable and preferred to proceeding in 50m visibility; (4) ENGINE READINESS: at minimum speed, engines must be on immediate readiness; (5) SOUND SIGNALS: Rule 35 fog signals must be sounded — one prolonged blast every 2 minutes (making way), two prolonged if stopped; (6) VTS NOTIFICATION: inform Dover Coastguard/CROSSMA of your situation; (7) COMPANY SMS: most tanker company SMS procedures require master to notify VTSO and office if proceeding in visibility below 0.5nm. BOTTOM LINE: 50m visibility is at the extreme threshold — seriously consider proceeding at minimum steerage outside the TSS lanes or anchoring in designated anchorage areas.

B. Rule 10 requires all vessels to maintain continuous progress through a TSS. Stopping or anchoring in any weather is prohibited under COLREG Rule 10.

C. At 50m visibility, the correct action is to proceed at full sea speed through the Dover Strait as quickly as possible to minimise time exposure to the hazardous visibility condition.

D. Anchoring in the middle of the Dover Strait TSS eastbound lane is the safest option at 50m visibility, as it removes you from being a moving collision hazard.

A. SAFE SPEED IN RESTRICTED VISIBILITY — Rule 6 assessment (COLREG Rule 6): safe speed requires consideration of: (a) state of visibility (300m — severely restricted); (b) traffic density (Dover Strait is one of the world's busiest waterways — separation scheme traffic plus local traffic); (c) manoeuvring ability — your vessel's stopping distance at 12 knots (a 140m bulk carrier may take 15+ ship lengths to stop); (d) background lighting at night; (e) draught — your squat in shallow Dover Strait approaches. AT 12 KNOTS WITH 300M VISIBILITY: stopping distance will greatly exceed 300m — you cannot stop within the distance you can see. Rule 8(e) requires reduction to minimum steerage way if necessary to avoid collision. IMMEDIATE ACTIONS: (1) Sound fog signal — one prolonged blast every 2 minutes (Rule 35a — power-driven vessel underway making way); (2) Reduce speed to safe speed — likely 5-6 knots or less to ensure vessel CAN STOP within visibility range; (3) Post extra lookout — Rule 5 — additional lookouts on bow in fog; (4) ARPA on — operating on appropriate scale, all targets tracked; (5) VHF Ch 16 / Ch 11 (Dover VTS DOVER COASTGUARD) monitored; (6) Navigation lights on; (7) Master already called — correct. Safe speed is your judgement call — document your reasoning in the log.

B. Safe speed in fog is defined as half the vessel's normal service speed. At 12 knots service speed, 6 knots is automatically the correct safe speed under COLREG Rule 6.

C. Rule 6 safe speed assessment applies only when vessels have radar — a vessel without radar is exempt from safe speed requirements in restricted visibility.

D. With visibility of 300m, the vessel should anchor immediately in the Dover Strait to await improvement, regardless of traffic density or depth.

A. RULE 19(d) — Action when radar contact detected (no visual contact): COLREG Rule 19(d): a vessel which detects by radar only another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists. If so, take avoiding action in ample time. The action must be: (a) A LARGE ALTERATION OF COURSE — Rule 19(d)(i): if possible, avoid an alteration of course to port for a vessel forward of the beam other than for a vessel being overtaken; (b) AVOID ALTERING COURSE TOWARDS A VESSEL ABEAM OR ABAFT THE BEAM — Rule 19(d)(ii); (c) REDUCE SPEED — reducing speed, stopping engines, or reversing may be needed. IN YOUR SCENARIO: CPA 0.1nm is a close-quarters situation. TCPA 8 minutes gives time for action. RECOMMENDED ACTION: (1) Reduce speed immediately (further — to minimum steerage); (2) Alter course to starboard — large alteration (minimum 30-40°) to open the CPA; (3) Sound appropriate fog signals; (4) Monitor ARPA to confirm action is working — CPA must open; (5) DO NOT alter to port (risk of swinging your bow into the other vessel's path); (6) VHF — if other vessel is a known contact, alert them, but do not rely on VHF agreement. Rule 19 is clear — radar action must be early, substantial, and effective.

B. With CPA 0.1nm and TCPA 8 minutes, the situation is not yet a close-quarters situation under COLREG Rules. Maintain course and speed while monitoring the target.

C. Call the other vessel on VHF Ch 16 and agree a port-to-port passing. Once verbal agreement is reached, no course alteration is necessary.

D. Stop engines and anchor immediately — Rule 19 requires vessels to anchor when a close-quarters situation develops in restricted visibility.