Part D — Sound and Light Signals
COLREGS Rule 34 — Maneuvering and Warning Signals
Rule 34 specifies the maneuvering and warning sound signals. Under COLREGS, these signals describe ACTION TAKEN. Under US Inland Rules, the same signals state INTENT. The five-or-more short blasts danger/doubt signal applies under both sets of rules.
Rule Text
A vessel in sight of another, when maneuvering as authorized or required by these Rules, shall indicate that maneuver by the following signals on her whistle: one short blast = altering course to starboard; two short blasts = altering course to port; three short blasts = operating astern propulsion. A vessel which fails to understand the intention or action of another vessel, or is in doubt whether sufficient action is being taken to avoid collision, shall indicate such doubt by giving at least five short and rapid blasts. This signal may be supplemented by a light signal of at least five short and rapid flashes. In a narrow channel or fairway when overtaking, specific signals apply.
What it means on the water
- →1 short blast: altering course to STARBOARD (COLREGS = action taken; Inland = intent).
- →2 short blasts: altering course to PORT.
- →3 short blasts: using ASTERN propulsion (NOT 'going astern' — propulsion may not yet produce sternway).
- →5+ short blasts: DANGER/DOUBT signal — used when in doubt or when other vessel not taking sufficient action.
- →COLREGS: signals are given when a maneuver is made (action). Inland: signals state INTENT (agreement required before maneuver).
- →Light signals (flashes) may supplement whistle signals.
Common exam mistakes
- ✗Confusing COLREGS signals (action) with Inland signals (intent) — a major exam trap.
- ✗Saying 3 blasts means 'going astern' — it means OPERATING ASTERN PROPULSION; the vessel may still be making headway.
- ✗Missing the light-signal option (rapid flashes) as a supplement to whistle signals.
USCG exam questions — Rule 34
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. A power-driven vessel in sight of another vessel alters course to starboard. What whistle signal is required under Rule 34?
- A.Two short blasts
- B.Three short blasts
- C.One short blast✓
- D.One prolonged blast
Why: Rule 34(a)(i) requires one short blast to mean 'I am altering my course to starboard.' Two short blasts signal a port alteration. Three short blasts signal engines going astern. This signal is used only when vessels are in sight of one another.
2. A vessel in doubt about whether another vessel's actions are sufficient to avoid collision should sound which signal under Rule 34(d)?
- A.One prolonged blast
- B.Two prolonged blasts followed by one short blast
- C.At least five short and rapid blasts on the whistle✓
- D.One prolonged blast followed by two short blasts
Why: Rule 34(d) prescribes at least five short and rapid blasts as the doubt or danger signal. This can be supplemented by at least five short and rapid flashes of a light. It is used when a vessel is in doubt about the sufficiency of action being taken to avert collision.
3. You are the give-way vessel and intend to pass a vessel on her starboard side in a narrow channel. Under Rule 34(c), what signal must you sound to propose this maneuver?
- A.One short blast
- B.Two prolonged blasts followed by one short blast✓
- C.One prolonged blast followed by one short blast
- D.Three short blasts
Why: Rule 34(c)(i) covers overtaking in a narrow channel where the overtaking vessel cannot pass without the other vessel taking action. To pass on the other vessel's starboard side, the overtaking vessel sounds two prolonged blasts followed by one short blast. One prolonged + two short = pass on the port side. Mutual agreement is confirmed by one prolonged, one short, one prolonged, one short from the vessel being overtaken.
4. You are the stand-on vessel in a crossing situation. The give-way vessel appears to be taking no action. You sound five or more short blasts. What are you signaling under Rule 34(d)?
- A.That you are altering course to starboard
- B.That you are operating astern propulsion
- C.That you are in doubt whether sufficient action is being taken to avoid collision✓
- D.That you are engaging in restricted maneuverability
Why: Five or more short and rapid blasts is the doubt or danger signal of Rule 34(d). As the stand-on vessel, you use this when in doubt that the give-way vessel is taking sufficient action. The signal can be supplemented by at least five flashes. It does not authorize you to take any particular action — it is a warning, not a maneuver signal.
5. A vessel on inland waters signals two short blasts. The other vessel answers with five short blasts. This means:
- A.The pass-to-starboard proposal is rejected; the vessels must use VHF to negotiate✓
- B.Agreement to the pass-to-starboard proposal is given
- C.The responding vessel is reversing its engines
- D.The responding vessel is overtaking
Why: Five or more short blasts is the danger signal under Inland Rule 34(d). When returned in response to a maneuvering proposal, it signals doubt or disagreement. Both vessels must slow, stop, or reverse as necessary until a safe passing agreement is reached.
6. Under 72 COLREGS, can a vessel in a narrow channel signal its intent to overtake before passing?
- A.No — COLREGS Rule 34 has no provision for an overtaking signal in a narrow channel
- B.Yes — two prolonged blasts followed by one short blast✓
- C.Yes — two short blasts to indicate port-side overtaking
- D.Yes — one prolonged blast to request sea room
Why: 72 COLREGS Rule 34 does not include an overtaking-proposal signal for narrow channels. This is an Inland Rules feature under Rule 34(c), reflecting the greater traffic density on U.S. rivers.
7. Under 72 COLREGS, if a give-way vessel in a crossing situation sounds two short blasts before altering course to port, this is:
- A.Correct — COLREGS requires the signal before the maneuver as a proposal
- B.Correct — it signals intent to pass to starboard
- C.An action signal announcing the course change to port that is already occurring✓
- D.Incorrect — COLREGS forbids sound signals in crossing situations
Why: Under 72 COLREGS, two short blasts are an action signal — they announce that the vessel IS altering course to port (not that she intends to). No agreement from the other vessel is required or expected under COLREGS, unlike the Inland intent-based system.
8. A power-driven vessel underway sounds three short blasts. This signal means the vessel is:
- A.Operating in restricted visibility
- B.Altering course to port
- C.Operating engines astern✓
- D.Requesting a bend or overtaking signal
Why: Under Rule 34(a), three short blasts mean 'I am operating my engines in astern propulsion.' This is a maneuvering signal used when vessels are in sight of one another.
Frequently asked questions
- What does three short blasts on a whistle mean?
- Three short blasts means the vessel is operating astern propulsion. It does not necessarily mean the vessel is moving astern — the propeller is in reverse but the vessel may still be moving forward due to momentum. Under both COLREGS and Inland Rules, three short blasts carry the same meaning.
- What is the difference between COLREGS and Inland maneuvering signals?
- Under COLREGS, maneuvering signals describe the action as it is being taken — one blast means 'I am altering course to starboard.' Under US Inland Rules, the same signals are signals of intent — one blast means 'I intend to leave you on my port side' — and the other vessel must respond with agreement before the maneuver can proceed safely.
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