You are OOW in restricted visibility. Describe your systematic ARPA management procedure for a vessel in a busy coastal area.

A. SYSTEMATIC ARPA MANAGEMENT in restricted visibility: (1) RANGE SCALE SELECTION: use two radar displays if available — one on 6nm scale (tactical — seeing immediate threats), one on 12nm scale (strategic — identifying developing situations early). Avoid using maximum range scales in fog — contacts at 24nm are not your immediate problem; (2) TARGET ACQUISITION: acquire all significant targets — set automatic acquisition zones to catch new contacts promptly; manually acquire small or slow targets that auto-acquisition misses; (3) TRACKING DATA: for each tracked target: record bearing (true), range, CPA, TCPA, true course, true speed. A target with CPA <1nm and TCPA <12 minutes warrants attention. CPA <0.5nm and TCPA <8 minutes = close-quarters developing; (4) TRAIL MANAGEMENT: use relative trails (typically 6-minute) to see target movement quickly — trails pointing toward your vessel indicate danger; (5) ARPA LIMITATIONS: be aware of — target swap (ARPA can confuse targets in congested areas); new target acquisition delay (ARPA takes 3-5 radar scans to establish a track — approximately 2-3 minutes, during which data is unreliable); small vessel detection (very small vessels or wave-pattern interference may not be detected). Guard zones should be set; (6) RADAR LOG: regular plots or ARPA data recordings — note significant targets and actions taken; (7) CROSS-CHECK: cross-check radar with ECDIS — confirm that charted hazards correlate with radar returns.

B. In restricted visibility, radar should be set to maximum range to provide the earliest possible warning of approaching vessels, allowing maximum reaction time.

C. ARPA target data is automatically logged by the VDR, so manual radar observation notes in restricted visibility are not required by COLREG or STCW.

D. In fog, rely on AIS rather than ARPA — AIS gives vessel identity, speed, and course in real time, while ARPA requires time to build a track before it is reliable.

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.