Conduct in Restricted Visibility

When Rule 19 applies

In short: Read look-out and safe speed and risk of collision and action to avoid collision first. COLREG Rule 19 is the whole of Part B, Section III. It governs vessels that are not in sight of one another in or near restricted visibility. In fog there is no give-way and no stand-on vessel: every vessel acts.

• COLREG Rule 19(a) — applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. You can be in clear weather and still be under Rule 19 if the other ship is hidden in a fog bank.
• Restricted visibility (COLREG Rule 3(l)): any condition where visibility is reduced by fog, mist, falling snow, heavy rainstorms, sandstorms or similar causes. In meteorology, fog means visibility under 1,000 m — see how fog forms.
• In sight (COLREG Rule 3(k)): only when one vessel can be observed visually from the other. A radar echo or an AIS target is not “in sight”.
• Where it sits in the structure of the COLREG: Section I (Rules 4–10) applies in any visibility; Section II (Rules 11–18) only to vessels in sight; Section III (Rule 19) to vessels not in sight.
• No stand-on vessel: the give-way / stand-on system of Rules 11–18 does not exist here. Both ships must act to avoid a close-quarters situation (MGN 369 (M+F) Amd 1).
• The moment you see the other vessel, Section II applies again (crossing, head-on, overtaking), even if the fog is still around you.
• Section I still applies in fog: look-out, safe speed, risk of collision, action to avoid collision, and the “not to impede” duties in narrow channels and TSS.

Safe speed, engines ready and Section I in fog

In short: As visibility drops: slow down to a safe speed, put the engines on standby, and apply the Section I rules with the fog in mind — radar plotting replaces visual compass bearings.

• COLREG Rule 19(b) — every vessel proceeds at a safe speed adapted to the restricted visibility. A power-driven vessel keeps her engines ready for immediate manoeuvre.
• In practice: tell the engine room as soon as visibility drops. On ships burning heavy fuel oil this can mean changing over to diesel oil, as before arriving in port.
• COLREG Rule 19(c) — when you apply Section I (Rules 4–10), have due regard to the restricted visibility. Example: you cannot take visual compass bearings in fog, so you use systematic radar observation to judge risk of collision.
• Radar is required by Rules 5, 6, 7, 8 and 19:
  • Rule 5 — look-out by all available means, radar included (plus sight and hearing).
  • Rule 6 — safe speed; 6(b) adds factors for vessels using radar.
  • Rule 7 — risk of collision: long-range scanning and systematic plotting. No assumptions on scanty radar information.
  • Rule 8 — avoiding action: early, substantial, seamanlike.
  • Rule 19 — conduct in restricted visibility.
• At management level, know both the integrity (processing) and the reliability (accuracy) of the radar information you base your decisions on.
• No COLREG figure for “safe speed” in fog: review it continuously. Higher speed = less time to decide whether risk of collision exists (MGN 369 (M+F) Amd 1).

Target detected by radar alone — Rule 19(d)

In short: A radar-only target: first decide whether a close-quarters situation is developing and/or risk of collision exists. If so, act in ample time. If you alter course, avoid turning to port for a vessel forward of the beam (unless you are overtaking her) and avoid turning towards a vessel abeam or abaft the beam.

• COLREG Rule 19(d) — a vessel that detects another by radar alone shall determine if a close-quarters situation is developing and/or risk of collision exists. If so, she takes avoiding action in ample time. If the action is an alteration of course, so far as possible avoid:
  • 19(d)(i) — an alteration to port for a vessel forward of the beam, other than a vessel being overtaken;
  • 19(d)(ii) — an alteration towards a vessel abeam or abaft the beam.
• Forward of the beam = relative bearing less than 090° or more than 270° (MGN 369 (M+F) Amd 1). “Abeam or abaft” = everything from 090° to 270° relative.
• Do not mix this with the 22.5° abaft the beam arc of Rule 13 (overtaking): Rule 13 is a Section II rule for vessels in sight. Under Rule 19 any target abaft the beam counts as “abaft”. This point is often debated — read the rule text.
• Your options: alter to starboard, reduce speed, stop or reverse the engines (COLREG Rule 8(e)), or a combination. Whatever the situation: slow down is almost always part of the answer.
• Principle: the most dangerous time is when you have no visual contact. Always ask: “where can I go to create distance?”
• Choose the side first when you plan the manoeuvre on the plot: starboard and port give different results, and Rule 19(d) rules some of them out.
• Make the alteration readily apparent on the other ship’s radar: not 1–2°, but you don’t need 90° or 180° either.

Risk of collision on the plot

• Sources, in order of value: TT/ARPA (range, bearing, course, speed — the primary method), AIS (type, heading, nav status — relies on GNSS), association of the two, then manual plot (slower, fewer targets, less accurate). See collision avoidance with radar.
• CPA/TCPA logic (radar plotting):
  • CPA > CPA limit → not dangerous;
  • CPA ≤ limit, TCPA > limit → no immediate danger, watch the TCPA;
  • CPA ≤ limit, TCPA ≤ limit → dangerous → decide and act.
• Examples: CPA limit 1.5 NM, target CPA 0.9 NM → a small alteration solves it. Limit 1 NM, target CPA 0.1 NM → a major problem. The radar flags dangerous targets in red even before you acquire them.
• The COLREG sets no minimum CPA or TCPA and no distance for “close quarters”: the company and the Master set them. Close quarters is a later stage than risk of collision (MGN 369 (M+F) Amd 1).
• A single plotted point is scanty information (Rule 7): ask for more plots before you decide. The next ones may show the target is opening.
• AIS helps identify a target but is not the basis for deciding risk of collision (MGN 369 (M+F) Amd 1) — see AIS and target association.

On the bridge: three radar targets in fog

• Target fine on the starboard bow, bearing steady, CPA 0.3 NM: forward of the beam → a bold alteration to starboard and/or reduce speed. Not to port (19(d)(i)).
• Target on the port bow, crossing, CPA small: still forward of the beam → no turn to port. Alter to starboard (passing astern of her) or slow down / stop.
• Target on the starboard quarter, closing: abaft the beam → no turn to starboard (that is towards her, 19(d)(ii)). An alteration to port, away from her, opens the distance.
• Slower ship ahead that you are overtaking: the only case where a turn to port for a vessel forward of the beam is allowed by 19(d)(i).

Hearing a fog signal — Rule 19(e)

In short: Hear a fog signal apparently forward of the beam, or can’t avoid close quarters with a vessel forward of the beam → reduce to bare steerage way, take all way off if necessary, and navigate with extreme caution until the danger is over.

• COLREG Rule 19(e) — except where it has been determined that risk of collision does not exist, every vessel that:
  • hears, apparently forward of her beam, the fog signal of another vessel, or
  • cannot avoid a close-quarters situation with another vessel forward of her beam,
  • shall reduce speed to the minimum at which she can be kept on her course (bare steerage way), shall if necessary take all her way off, and shall navigate with extreme caution until danger of collision is over.
• Fog signal ≠ radar echo. A radar echo forward of the beam at, say, 3 NM is a 19(d) case: assess, then take early avoiding action (often an alteration to starboard). A fog signal heard forward of the beam means the vessel is close → 19(e): slow right down or stop.
• Fog signal abaft the beam: 19(e) does not apply. You are not required to stop; keep listening and plotting, and don’t turn towards it (19(d)(ii) if you also have her on radar).
• The direction of a sound signal in fog is hard to judge, so allow more time. Keep a listening watch on the bridge wings and use sound-reception equipment where fitted (MGN 369 (M+F) Amd 1).
• Your own fog signals: COLREG Rule 35, at intervals of not more than 2 minutes, in or near restricted visibility, by day and night. Crew or passenger discomfort is not a reason to stop sounding them (MGN 369 (M+F) Amd 1).

On the bridge: fog, target ahead

• Dense fog in a narrow channel. A container ship 2.5 NM ahead, CPA 0.8 NM, no answer on VHF.
• ✅ Reduce speed and prepare to take avoiding action: target forward of the beam with close-quarters risk → bare steerage way, all way off if needed (19(e)). If you alter, not to port (19(d)(i)). Both ships manoeuvre: there is no stand-on vessel.
• ❌ “Maintain course and speed” (that is a Section II idea) · ❌ “Increase speed and overtake”.
• If an answer option says “head-on”, ignore it: it only tells you the target is forward of the beam. Head-on (Rule 14) is for vessels in sight.

Bridge procedure in restricted visibility — MGN 315

In short: When visibility drops, the OOW follows the COLREG, calls the Master, switches on lights, starts fog signals, uses the radar, posts an extra look-out, and proceeds at safe speed with engines ready.

• MGN 315 (M), bridge procedure B13 — in restricted visibility the OOW:
  1. complies first with the COLREG;
  2. informs the Master;
  3. exhibits navigation lights (also by day — COLREG Rule 20(c));
  4. sounds the fog signals;
  5. operates and uses the radar;
  6. posts an extra look-out at all times;
  7. proceeds at a safe speed with the engines ready for immediate manoeuvre.
• Steering: switch to manual steering in restricted visibility, as in heavy traffic and critical manoeuvres (MGN 315). A qualified helmsperson must be available.
• Sole look-out: only by day, and only when the Master judges it safe after considering weather, visibility, traffic density and dangers to navigation (MGN 315, STCW). In restricted visibility the OOW is not the only look-out.
• Typical Master’s standing orders: call the Master if visibility falls below 3 NM and put the engines on standby; don’t rely on radar alone for navigation; fix the position by more than one method, not only GPS; keep the GMDSS radio watch.
• A full bridge example: radar(s) on and plotting, extra look-out on the bridge wing (sight and hearing), helmsman on manual, engine room on standby, lights on, fog signal running, Master on the bridge, speed reduced, position fixed by radar ranges as well as GNSS.