1.17 Sound & Light Signals + Distress Signals (Rules 32–37, Annex IV)

Rules 32-37 and Annex IV: Sound, Light, and Distress Signals

Part D of the Rules turns collision avoidance into an audible language. You must know the equipment, the blast vocabulary, the crucial International-vs-Inland split in maneuvering signals, the fog-signal timetable, and the recognized distress signals. This is prime 90%-module material — the patterns are exact and heavily tested.

Rule 32 — the vocabulary of blasts

• A short blast lasts about 1 second.
• A prolonged blast lasts about 4 to 6 seconds.
• "Whistle" means any appliance capable of producing the prescribed blasts.

Rule 33 — required equipment

A vessel 12 m or more must carry a whistle and a bell; a vessel 100 m or more must also carry a gong whose tone cannot be confused with the bell. A vessel less than 12 m need not carry these but must have some other means of making an efficient sound signal.

Rule 34 — maneuvering and warning signals (in sight of one another)

Here the two rule sets diverge, and the difference is a guaranteed exam point. The blasts are the same; their meaning is not:

Under International rules the signal announces an action already being taken and the other vessel is not required to answer. Under Inland rules the signal announces an intention, and the other vessel must answer with the same signal to agree (or sound the danger signal if she disagrees). Memorize the frame: International = action; Inland = intent + agreement.

Doubt / danger signal: if either vessel doubts the other's intentions or whether enough is being done to avoid collision, she sounds at least five short and rapid blasts — the universal "danger / I don't understand you" signal, identical in both rule sets.

Blind bends: a vessel approaching a bend or an obstruction where other vessels may be hidden sounds one prolonged blast, answered by any approaching vessel within hearing with one prolonged blast.

Overtaking in a narrow channel (International, Rule 34(c)): the overtaker signals two prolonged + one short ("I intend to overtake on your starboard side") or two prolonged + two short ("…on your port side"); the vessel about to be overtaken agrees with one prolonged, one short, one prolonged, one short. (On Inland waters this is instead handled with one/two short blasts.)

Rule 35 — sound signals in restricted visibility (fog)

This is a timetable to memorize exactly. Signals are given at intervals of not more than 2 minutes unless noted:

Notice a group of vessels — NUC, RAM, CBD, sailing, fishing, and towing — all share the one-prolonged-plus-two-short signal. A quick check: a vessel making way under power gives one prolonged; if she is stopped she gives two prolonged.

Rule 36 — signals to attract attention

Any vessel may make light or sound signals to attract attention, provided they cannot be mistaken for an authorized signal, and may direct a searchlight toward the danger — but not in a way that embarrasses another vessel.

Rule 37 and Annex IV — distress signals

When a vessel is in distress and requires assistance she uses or exhibits the signals in Annex IV. Any one of these means "I need help." The commonly tested ones:

• A gun or explosive signal fired at intervals of about a minute.
• A continuous sounding of any fog-signaling apparatus.
• Rockets or shells throwing red stars, one at a time at short intervals.
• "MAYDAY" spoken by radiotelephone; "SOS" (· · · — — — · · ·) by any signaling method.
• The flag signal "NC" (November-Charlie) of the International Code.
• A square flag with a ball (or anything resembling a ball) above or below it.
• Flames on the vessel (e.g., a burning tar barrel).
• A red parachute rocket or a red hand-held flare.
• Orange-colored smoke.
• Slowly and repeatedly raising and lowering outstretched arms.
• EPIRB activation, a DSC distress alert on VHF Ch 70 or MF/HF, and distress alerts via Inmarsat/GMDSS.
• An orange dye marker in the water.

Trap: the color of pyrotechnic distress signals is red (flares/rockets) or orange (smoke). A white flare is not a distress signal — it is used to signal your presence or warn of a close-quarters situation.

Worked example

In thick fog you hear, from ahead, one prolonged blast repeating roughly every 90 seconds. Diagnose it: a power-driven vessel underway and making way. (Two prolonged would mean she was stopped; one-prolonged-plus-two-short would mean an encumbered vessel such as a tug or fishing vessel.) Combine this with Rule 19 — slow to steerageway and be ready to stop until the situation resolves.

Traps

• International = action; Inland = intent + agreement. Same blasts, different meaning and answer requirement.
• Five short blasts = doubt/danger, in both rule sets.
• Fog: one prolonged = power making way; two prolonged = power stopped; one prolonged + two short = NUC/RAM/CBD/sail/fish/tow.
• Anchored = bell 5 seconds every minute (not a whistle signal).
• Red flares/rockets and orange smoke are distress; a white flare is not.