Manoeuvring, Warning and Fog Signals

Blasts, whistle, bell and gong — Rules 32 and 33

In short: Read Lights and Shapes of Special Vessels and How to Read Them, Narrow Channels and Traffic Separation Schemes and Conduct in Restricted Visibility first. Every signal is built from short and prolonged blasts. What you must carry depends on length: whistle from 12 m, bell from 20 m, gong from 100 m.

• Notation on this page: • = short blast, — = prolonged blast.
• Short blast = about 1 second (COLREG Rule 32(b)).
• Prolonged blast = 4 to 6 seconds (COLREG Rule 32(c)).
• Whistle = any sound appliance that can make these blasts and meets Annex III (COLREG Rule 32(a)).
• Equipment by length (COLREG Rule 33(a)):
  • 12 m or more: a whistle;
  • 20 m or more: a whistle and a bell;
  • 100 m or more: also a gong, whose sound cannot be confused with the bell. Only from 100 m — a common oral question.
• Bell and gong may be replaced by other equipment with the same sound, as long as manual sounding is always possible (COLREG Rule 33(a)).
• Under 12 m: not obliged to carry whistle or bell, but must have some other means of making an efficient sound signal (COLREG Rule 33(b)). So your 10 m tender does need a sound signal — an air horn, for example.
• How far a whistle is heard (COLREG Annex III, audibility range, for information — it can be much less in real fog):

• Bigger ships have lower-pitched whistles: frequency range 70–700 Hz, lowest for vessels of 200 m or more (COLREG Annex III).
• Bell and gong: sound pressure at least 110 dB at 1 m; bell mouth at least 300 mm on vessels of 20 m or more (COLREG Annex III).

Manoeuvring signals — Rule 34(a) and (b)

In short: Only for vessels in sight of one another. A power-driven vessel that alters course or goes astern as the Rules allow or require shall say so: 1 short = starboard, 2 short = port, 3 short = astern. Never in fog.

• COLREG Rule 34(a) — power-driven vessel underway, vessels in sight, manoeuvring as authorised or required by the Rules:
  • • one short: “I am altering my course to starboard”;
  • • • two short: “I am altering my course to port”;
  • • • • three short: “I am operating astern propulsion”.
• Note the words: “astern propulsion”, not “going astern”. The ship may still be moving ahead.
• It is a power-driven vessel rule. A yacht under sail alone does not give it; the same yacht motoring is a power-driven vessel and does.
• COLREG Rule 34(b) — any vessel may add light signals to the whistle signals, repeated as needed while she manoeuvres: 1 flash starboard, 2 flashes port, 3 flashes astern.
  • Each flash about 1 s; interval between flashes about 1 s; interval between signals not less than 10 s.
  • The light, if fitted: all-round white, visible at least 5 NM, as in Annex I.
• In restricted visibility vessels are not in sight, so Rule 34(a) does not apply. Only the Rule 35 fog signals are used.

On the bridge: head-on in clear weather

• A power-driven vessel is fine on your bow, head-on (COLREG Rule 14). You alter to starboard and sound • one short blast.
• If you also stop and put the engine astern, add • • •.
• Night, noisy port: you may show the same with the white manoeuvring light — 1 flash for starboard.

Overtaking in a narrow channel and bend signals — Rule 34(c), (e) and (f)

In short: In a narrow channel, the overtaking vessel asks with — — • (on your starboard side) or — — • • (your port side). The vessel ahead agrees with — • — • (Morse C). At a blind bend: — one prolonged, answered by —.

• COLREG Rule 34(c) — vessels in sight in a narrow channel or fairway, when overtaking needs the vessel ahead to act (COLREG Rule 9(e)):
  • — — • two prolonged + one short: “I intend to overtake you on your starboard side”;
  • — — • • two prolonged + two short: “I intend to overtake you on your port side”;
  • — • — • prolonged, short, prolonged, short: the vessel being overtaken agrees.
• Memory aid: the number of short blasts matches Rule 34(a) — 1 = starboard, 2 = port. And — • — • is Morse C, “yes” in the International Code of Signals.
• If the vessel ahead is in doubt, she may sound the doubt signal • • • • • instead (COLREG Rule 9(e)(i), 34(d)).
• Agreement does not free the overtaking vessel: she still keeps clear (COLREG Rule 13 — see Overtaking, Head-on and Crossing Situations).
• COLREG Rule 34(e) — nearing a bend or an area where other vessels may be hidden by an obstruction: one prolonged blast —. Any vessel approaching round the bend that hears it answers —. Rule 9(f) adds: navigate with particular alertness and caution.
• COLREG Rule 34(f) — if a vessel has whistles more than 100 m apart, she uses only one for manoeuvring and warning signals (two whistles would confuse the direction).

The doubt signal and signals to attract attention — Rules 34(d) and 36

In short: Don’t understand what the other ship is doing, or doubt she is doing enough? Sound at least five short and rapid blasts. To attract attention, use a signal that cannot be mistaken for any other signal — never strobe lights.

• COLREG Rule 34(d) — vessels in sight, approaching each other: if either one fails to understand the other’s intentions or actions, or doubts that she is taking enough action to avoid collision, she shall sound at least five short and rapid blasts • • • • •.
• She may add a light signal of at least five short and rapid flashes.
• Typical use: the stand-on vessel sees the give-way vessel doing nothing (COLREG Rule 17(a)(ii) — see Give-way, Stand-on and Responsibilities between Vessels). Sound the doubt signal first, then act if needed.
• It is a “shall”, not a “may”. It is not a distress signal.
• COLREG Rule 36 — any vessel may make light or sound signals to attract attention, if they cannot be mistaken for any signal in the Rules. She may also point her searchlight towards the danger, without dazzling any vessel.
• A light used to attract attention must not look like an aid to navigation. Avoid high-intensity intermittent or revolving lights such as strobes (COLREG Rule 36).
• Distress signals are COLREG Rule 37 and Annex IV: see the Distress Signals topic.

Fog signals underway — Rule 35(a) to (f) and (k)

In short: In or near restricted visibility, by day or night, every vessel gives her fog signal at intervals of not more than 2 minutes. Power-driven making way —; stopped — —; the “difficult” vessels — • •; manned towed vessel — • • •; pilot adds • • • •.

• COLREG Rule 35 applies in or near an area of restricted visibility, by day or night. Intervals are not more than 2 minutes unless stated.

• — • • is Morse D: “keep clear of me, I am manoeuvring with difficulty”. All the vessels that can’t easily get out of your way use it. Sailing vessels too, even if Rule 18 ranks them below the others.
• The towed vessel sounds — • • • (Morse B — “B for behind”), when practicable immediately after the towing vessel’s — • • (COLREG Rule 35(e)). Heard together: — • • then — • • • = a tow is passing.
• • • • • is Morse H, flag H = “I have a pilot on board”. The pilot vessel adds it to her —, — — or anchor signal (COLREG Rule 35(k)).
• Under 12 m: not obliged to give these signals, but if not, another efficient sound signal at intervals of not more than 2 minutes (COLREG Rule 35(j)).
• Don’t stop sounding because crew or passengers are disturbed: discomfort is not an acceptable reason (MGN 369 (M+F) Amd 1, 7.3). Missing fog signals contributed to a 2016 collision on the River Humber (MGN 369, 7.2).
• Offshore units (connected platforms) sound Morse U • • — instead of Rule 35 signals (MGN 369, 7.4).

Fog signals at anchor and aground — Rule 35(d), (g) to (j)

In short: At anchor: bell rapidly for about 5 s, at intervals of not more than 1 minute; 100 m or more: bell forward, then gong aft. Aground: the same, plus 3 separate strokes on the bell before and after.

• At anchor (COLREG Rule 35(g)): ring the bell rapidly for about 5 seconds at intervals of not more than 1 minute (not 2!).
• 100 m or more at anchor: bell in the forepart, then immediately the gong rapidly for about 5 s in the after part (COLREG Rule 35(g)). This is why the gong is required only from 100 m.
• At anchor she may also sound • — • (one short, one prolonged, one short) to warn an approaching vessel of her position and the risk of collision (COLREG Rule 35(g)). Morse R — “R for riding at anchor”.
• Fishing at anchor and RAM working at anchor: they sound — • • instead of the bell (COLREG Rule 35(d)). Their work still limits them.
• Aground (COLREG Rule 35(h)): the anchor bell (and gong if 100 m or more), plus three separate and distinct strokes on the bell immediately before and after the rapid ringing: 3 strokes — ring — 3 strokes. She may add a suitable whistle signal.
• 12 m to under 20 m: not obliged to give the bell signals at anchor or aground, but if not, another efficient sound signal at intervals of not more than 2 minutes (COLREG Rule 35(i)).
• Under 12 m: same idea, COLREG Rule 35(j).

On the bridge: anchor watch in fog

• Making the right fog signals is one of the OOW’s duties at anchor, with: anchor lights burning, anchor ball by day, good GMDSS radio watch, checks for a dragging anchor, second anchor ready to let go, gangway, watching boats arriving and leaving, and calling the Master at once if the vessel is in danger.
• 120 m ship at anchor, fog comes in: bell forward for 5 s, then gong aft for 5 s, at least every minute. Set a timer or use the automatic fog signal panel.
• A target on radar heads straight for you: add • — • on the whistle to warn her.

Hearing a fog signal — Rule 19(e) and MGN 369

In short: A fog signal heard forward of the beam means a vessel is close: reduce to bare steerage way and stop if necessary. Don’t confuse it with a radar echo at 3 NM, and don’t stop for a signal abaft the beam.

• COLREG Rule 19(e) — unless risk of collision has been ruled out, a vessel that hears a fog signal apparently forward of her beam reduces to the minimum speed to keep her course, takes all way off if necessary, and navigates with extreme caution until the danger is over. Full detail in Conduct in Restricted Visibility.
• Exam trap: radar echo ahead at 3 NM = Rule 19(d) — assess and take early action. Fog signal heard ahead = Rule 19(e) — slow right down or stop. Fog signal abaft the beam: you are not required to stop.
• Keep an effective listening watch; use sound reception equipment if fitted, for early detection (MGN 369 (M+F) Amd 1, 5.1.5).
• The direction of a sound in fog is hard to judge: allow more time to decide (MGN 369, 5.1.5). Wind turbines make noise that can mask fog signals (MGN 369, 7.5).
• Hear — • •? The other vessel may be limited in how she can manoeuvre: allow for it (MGN 369, 11.2).
• You can see a vessel that is sounding fog signals? Assume she cannot see you and is following the restricted-visibility rules (MGN 369, 11.3).