Single-letter signals and what they mean
1The lesson in plain words
Twenty-five letters carry urgent or common meanings that every officer must know at sight. Ten of them may be sounded only as the COLREGs allow.
Manoeuvring and keep clear
E I am altering my course to starboard. I I am altering my course to port. S I am operating astern propulsion; that is not the same as moving astern. M My vessel is stopped and making no way through the water. D Keep clear of me; I am manoeuvring with difficulty. T Keep clear of me; I am engaged in pair trawling. J I am on fire and have dangerous cargo on board: keep well clear of me, or I am leaking dangerous cargo.
Orders and dangers
L You should stop your vessel instantly. X Stop carrying out your intentions and watch for my signals. U You are running into danger. K I wish to communicate with you. Y I am dragging my anchor. F I am disabled; communicate with me. V I require assistance. W I require medical assistance. O Man overboard.
Port and pilotage
G I require a pilot. H I have a pilot on board. Z I require a tug. P In harbour: all persons should report on board before departure. Q My vessel is healthy and I request free pratique (public-health clearance). B I am taking in, discharging or carrying dangerous goods. A I have a diver down; keep well clear at slow speed.
Yes, no and fishing
C means yes. N means no visually or by sound; use ‘NO’ by voice. R has no single-letter meaning. Fishing vessels close together on the grounds use G for ‘I am hauling nets’ and Z for ‘I am shooting nets’. At sea, fishing vessels may use P for ‘My nets have come fast upon an obstruction’. As a sound signal, P means ‘I require a pilot’.
Sound and complements
B, C, D, E, G, H, I, S, T and Z are asterisked: sound them only in compliance with the COLREGs. Numeral complements give A bearing, C course, D date, G longitude, L latitude, R distance in nautical miles, S speed in knots, T local time, V speed in kilometres per hour and Z Coordinated Universal Time (UTC). K with one numeral selects how you want to communicate.
2Key data
- No single-letter meaning
- R
- By sound only per COLREG
- B, C, D, E, G, H, I, S, T, Z (asterisked)
- K + one numeral
- 1 hand flags/arms, 2 loud hailer, 3 Morse lamp, 4 sound
- Position letters
- L + 4 figures latitude; G + 4 or 5 figures longitude
- Bearing / course / speed
- A + 3 figures; C + 3 figures; S knots; V km/h
- Time
- T + 4 figures local time; Z + 4 figures UTC (GMT in the book)
3Key points
- 1
Know every single-letter meaning at sight; R has none.
- 2
S means astern propulsion is operating, not that the ship is moving astern.
- 3
Fishing meanings: G hauling and Z shooting nets when close together on the grounds; P nets obstructed at sea.
- 4
Ten asterisked letters may be sounded only as the COLREGs allow.
4Frequent mistakes
Wrong: Flag H means ‘I require a pilot’.
Right: H means ‘I have a pilot on board’. G means ‘I require a pilot’.
Wrong: Flag D means ‘I am in distress’.
Right: D means ‘Keep clear of me; I am manoeuvring with difficulty’. Distress by Code signal is the group NC.
Wrong: Signal N by voice for ‘no’ on the radio.
Right: N is for visual or sound signalling. By voice or radio the negative is ‘NO’.
5Practice case & exam keys
In a crowded anchorage at night, a ship nearby starts flashing dot-dot-dash (U) at you, repeatedly. Your anchor watch reports the bearing of the breakwater light is changing steadily. What is the ship telling you, and what do you do?
Show the answer
U means ‘You are running into danger’. It does not identify the cause. Alert the master, check your position and movement against nearby hazards, and clarify the warning with the other ship. Do not infer that your anchor is dragging, or infer a direction of movement, from one changing shore bearing.
Exam keys
- E starboard, I port, S astern propulsion; D and T keep clear; L stop instantly.
- G pilot required, H pilot on board, Q free pratique, O man overboard, V assistance, W medical.
- C yes, N no (visual or sound), R no meaning; G, P, Z fishing meanings.
- Asterisked B C D E G H I S T Z: by sound only in compliance with COLREG.
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