In fog, you notice the ECDIS track is diverging from the radar picture — coastal returns on radar do not match the ECDIS coastline. What do you do?

A. RADAR vs ECDIS DISCREPANCY IN FOG — ACTIONS: A divergence between radar returns and ECDIS charted features is a serious concern. Possible causes: (1) GPS ERROR: GPS may be providing a wrong position due to: signal spoofing; multipath error; HDOP (Horizontal Dilution of Precision) high in current satellite geometry; antenna fault; (2) CHART DATUM ERROR: ECDIS chart and GPS may use different datums (WGS84 vs local datum). If the chart has not been converted to WGS84, a systematic offset will appear. Check chart datum in ECDIS chart information; (3) RADAR ADJUSTMENT ERROR: the radar bearing/range rings may be slightly misaligned due to gyro error on compass card; (4) PAPER CHART CROSS-CHECK: immediately plot your position on paper chart using radar ranges and bearings to charted features — this gives an independent position; (5) NAVTEX: check NAVTEX for any navigational warnings in the area (bank or shoal not charted, buoy off station); (6) REDUCE SPEED: immediately. If you cannot trust your position, you cannot confirm you are clear of hazards; (7) CROSS-CHECK: use all available methods — radar, GPS, ECDIS, celestial (if stars available), depth sounder (compare to charted depths), DECCA (if available); (8) MASTER CALL: immediately; (9) ANCHOR: if position is genuinely uncertain in shallow/hazardous waters — anchor and resolve the discrepancy.

B. ECDIS is always more accurate than radar. If they diverge, follow ECDIS position and assume the radar returns are from shallow water features not shown on the chart.

C. Radar coastal returns are reflections — they sometimes show features displaced by wave refraction in fog. Accept the GPS/ECDIS position as accurate and continue.

D. Average the ECDIS and radar positions — the truth is somewhere between the two. Plot the averaged position and continue the approach.

A. COLREG RULE 19 — CONDUCT IN RESTRICTED VISIBILITY: Rule 19 applies to ANY vessel not in sight of another. Key requirements: (1) RULE 19(b) — SAFE SPEED: proceed at a safe speed adapted to prevailing circumstances and restricted visibility. The vessel must be able to take proper and effective action to avoid collision, and stop within an appropriate distance; (2) RULE 19(c) — RADAR: have due regard to prevailing circumstances, including the limitations of radar equipment; (3) RULE 19(d) — RADAR-ONLY CONTACT: a vessel that detects by radar only another vessel shall determine if a close-quarters situation is developing. If so — take early, substantial avoiding action: (i) an alteration of course to port for a vessel forward of the beam is to be AVOIDED (except when overtaking); (ii) avoid altering course toward a vessel abeam or abaft the beam; (4) RULE 19(e) — SOUND SIGNAL WARNING: if a sound signal is heard apparently forward of the beam and its vessel cannot be seen — reduce to minimum speed or stop. Take all way off if necessary; (5) RULE 35 — FOG SIGNALS: one prolonged blast (4-6 seconds) every 2 minutes when underway making way. Two prolonged blasts (2-second interval) every 2 minutes when underway but stopped. RULE 19 DOES NOT APPLY RULES 11-18 (in-sight rules). There is no give-way/stand-on in restricted visibility. All vessels take action to avoid collision.

B. Rule 19 suspends all other COLREG rules in fog. No vessel has right of way in fog, and any vessel may alter course in any direction to avoid collision.

C. Rule 19 requires vessels in restricted visibility to stop and anchor until visibility improves to at least 1nm before proceeding.

D. In restricted visibility, the stand-on vessel (Rule 17) must maintain course and speed even in fog. Rule 19 only applies to give-way vessels.

A. RULE 35 FOG SIGNALS — CORRECT SIGNALS: (a) POWER VESSEL UNDERWAY MAKING WAY (Rule 35a): ONE prolonged blast (4-6 seconds) — every 2 minutes; (b) POWER VESSEL UNDERWAY BUT STOPPED (Rule 35b): TWO prolonged blasts with 2-second interval — every 2 minutes; (c) VESSEL AT ANCHOR (Rule 35g): rapid ringing of bell for approximately 5 seconds — every 1 minute. Vessels of 100m+ ALSO sound a gong aft for 5 seconds after the bell. A vessel at anchor MAY ALSO sound "short-long-short" (Morse R —. — .) as a warning to approaching vessels; (d) VESSEL AGROUND (Rule 35h): three separate bell strokes, THEN rapid ringing of bell for 5 seconds, THEN three separate bell strokes — every 1 minute. This sequence distinguishes a vessel aground from one merely at anchor. ADDITIONAL SIGNALS: sailing vessel under sail — Rule 35c: one prolonged + two short blasts every 2 minutes (this same signal is also used by vessels restricted in ability to manoeuvre, constrained by draught, not under command, and towing/being towed — Rule 35d/e); pilot vessel — Rule 35g: normal fog signal + four short blasts as identity signal.

B. All vessels in restricted visibility sound one prolonged blast every 2 minutes regardless of their status. Rule 35 makes no distinction between underway, stopped, or at anchor.

C. A vessel at anchor does not need to sound fog signals provided she has all-round white anchor lights displayed and is monitoring VHF Ch 16.

D. Two short blasts is the correct fog signal for a power vessel underway making way. One prolonged blast is used only by sailing vessels.