Maneuvering signals, fog signals by vessel type, and distress signals — the most tested block in Part D of the OUPV exam. Know the blasts cold.
Rules 32–37 govern every sound signal requirement under ColRegs. Rule 32 defines the equipment and signal types. Rule 34 covers maneuvering and warning signals between vessels in sight of one another. Rule 35 covers fog signals — sounds required in or near restricted visibility regardless of time of day. Rule 37 and Annex IV list recognized distress signals.
Rules 32–37
Complete scope of Part D — Sound & Light Signals
High
Exam frequency — fog and maneuvering signals tested every exam
2 min
Standard fog signal interval for power, sail, fishing, and towing vessels
Short Blast
A blast of the whistle lasting approximately one second. Short blasts are used for maneuvering signals — one, two, three, or five or more short blasts each carry a specific meaning.
Prolonged Blast
A blast of the whistle lasting four to six seconds. Prolonged blasts are used in fog signals and for leaving a berth or dock. The interval is longer and distinctly different from a short blast.
Whistle
Any installed sound signaling appliance capable of producing the required blasts. For vessels under 12 meters, a whistle is required; for vessels 20 meters and over, both a whistle and a bell are required; vessels 100 meters and over must also carry a gong.
Used when vessels are in sight of one another. These are not fog signals — they are action signals and must be accompanied by a flashing light signal under Inland Rules.
| Signal | Meaning | Notes |
|---|---|---|
| 1 short blast | I am altering my course to starboard | International & Inland |
| 2 short blasts | I am altering my course to port | International & Inland |
| 3 short blasts | I am operating astern propulsion | Not a distress signal |
| 5+ short blasts | Danger / doubt signal — I do not understand your intentions | Always means danger or doubt — never ignore |
| 1 prolonged blast | Leaving a berth or dock | Also: power vessel in restricted visibility (fog signal) |
Inland Rules — agreement required
Under Inland Rules, a maneuvering signal must be answered with the same signal by the other vessel to indicate agreement. If the other vessel does not agree or does not understand, the danger signal (5+ short blasts) must be sounded. International Rules do not require an agreement reply.
When two power-driven vessels are meeting head-on or nearly head-on in inland waters, both vessels must signal their intended action and await agreement before maneuvering:
A vessel approaching a bend or channel obstruction where other vessels may be hidden must sound 1 prolonged blast. Any approaching vessel on the other side must reply with 1 prolonged blast. Both vessels then proceed with caution.
Under Inland Rules, every maneuvering signal sounded by whistle must be accompanied by a flashing light visible for at least 5 miles. The flash duration matches the blast duration — one flash per short blast, one prolonged flash per prolonged blast. International Rules do not require the accompanying light signal.
Sounded in or near restricted visibility — fog, heavy rain, haze — at any time of day. These are NOT maneuvering signals. Know every vessel type cold.
| Vessel Type | Signal | Interval |
|---|---|---|
| Power vessel underway — making way | 1 prolonged blast | Every 2 min |
| Power vessel underway — stopped, not making way | 2 prolonged blasts (~2 sec apart) | Every 2 min |
| Sailing vessel underway | Prolonged – short – short (▬ • •) | Every 2 min |
| Fishing vessel (engaged in fishing) | Prolonged – short – short (▬ • •) | Every 2 min |
| Not Under Command (NUC) | Prolonged – short – short (▬ • •) | Every 2 min |
| Restricted in Ability to Maneuver (RAM) | Prolonged – short – short (▬ • •) | Every 2 min |
| Vessel constrained by draft (CBD) | Prolonged – short – short (▬ • •) | Every 2 min |
| Vessel towing or pushing ahead | Prolonged – short – short (▬ • •) | Every 2 min |
| Vessel being towed (if manned) | Prolonged – short – short – short (▬ • • •) | Every 2 min |
| Vessel at anchor — under 100m | Rapid bell ringing ~5 seconds | Every 1 min |
| Vessel at anchor — 100m and over | Bell rapidly forward + gong rapidly aft | Every 1 min |
| Vessel aground | 3 bell strokes + rapid bell + 3 bell strokes | Every 1 min |
Memory anchor: prolonged-short-short
Six categories share the same fog signal — sailing, fishing, NUC, RAM, CBD, and towing. The vessel being towed is distinct: prolonged-short-short-short (one extra short). Anchor bell is every 1 minute, not 2.
Use any distress signal available. These signals may not be used for any other purpose and must not be used unless distress or urgency assistance is required.
5+ blasts always means danger or doubt
Five or more short blasts is the universal danger/doubt signal. It means 'I do not understand your intentions' or 'I doubt your action is sufficient to avoid collision.' It is NEVER a maneuvering signal — it always means stop and reassess.
Fog signal interval — 2 minutes (power, sail, fishing, towing)
Power vessel making way, stopped, sailing vessel, fishing vessel, NUC, RAM, CBD, and towing vessel all use a 2-minute interval. The only exception is the anchor bell and gong — every 1 minute.
Anchor bell — every 1 minute
A vessel at anchor sounds the bell rapidly for about 5 seconds every 1 minute — not 2 minutes. Vessels over 100m also sound a gong rapidly aft. Vessels aground add 3 distinct strokes before and after the rapid bell ringing.
3 short blasts ≠ distress
Three short blasts means 'I am operating astern propulsion.' It is a maneuvering signal, not a distress signal. Distress is signaled by continuous sounding of the fog signal, MAYDAY, flares, EPIRB, and other Annex IV methods.
Maneuvering signals require in-sight condition
Rule 34 maneuvering signals (1, 2, 3, 5+ short blasts) apply only when vessels are in sight of one another. In fog or restricted visibility, Rule 35 fog signals apply — not Rule 34 maneuvering signals.
Three short blasts mean 'I am operating astern propulsion' — that is, the vessel's engines are running in reverse. This is a maneuvering signal under Rule 34 and is NOT a distress signal. It is sounded when a vessel in sight of another vessel is using astern propulsion, regardless of whether the vessel is actually moving astern through the water.
A power-driven vessel making way through the water in or near restricted visibility sounds 1 prolonged blast at intervals of not more than 2 minutes (Rule 35). A power-driven vessel underway but stopped (not making way through the water) sounds 2 prolonged blasts in succession, with an interval of about 2 seconds between them, also at intervals of not more than 2 minutes.
Distress signals include: continuous sounding of the fog signal apparatus; the international code signal NC (Foxtrot-Charlie flags); slowly and repeatedly raising and lowering outstretched arms; orange smoke (day); red flares or rockets (night); MAYDAY transmitted on VHF Channel 16; and activation of an EPIRB. A gun or other explosive signal fired at one-minute intervals and flames on the vessel also qualify. No single signal is exclusive — use what is available.
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