1.17 Sound Signals — Maneuvering & Warning (Rules 32–34)
Key Takeaways
- Rule 32: short blast ≈ 1 second; prolonged blast = 4–6 seconds; 'whistle' means any prescribed sound-signaling appliance.
- Rule 33 equipment by length: ≥12 m whistle; ≥20 m whistle + bell; ≥100 m whistle + bell + gong; <12 m some efficient sound signal.
- Rule 34 when vessels are in sight: International 1/2/3 short = action (alter starboard / alter port / astern propulsion); Inland meeting/crossing 1/2 short = intent (leave you on my port / starboard side) with agreement required.
- International narrow-channel overtaking uses two prolonged + one/two short; agreement is prolonged-short-prolonged-short. Inland overtaking uses one/two short intent signals with matching agreement.
- Danger/doubt = at least five short and rapid blasts (optional matching light flashes); bend/obscured channel = one prolonged blast, answered the same.
Why Sound Signals Matter on Q100
On the ONC06 Master Less Than 100 GRT path, Q100 Rules of the Road is 50 questions at 90%. Part D (Rules 32–37) is pure high-yield: blast counts, International-versus-Inland meanings, and whether vessels are in sight. Confusing "I am altering" with "I intend to leave you" fails easy-looking items and causes real harbor collisions.
Rules 32–34 cover definitions, equipment, and maneuvering/warning signals when vessels can see each other. Fog signals are Rule 35 (next section) — do not mix those banks.
Rule 32 — Definitions
| Term | Meaning |
|---|---|
| Whistle | Any sound-signaling appliance capable of producing the prescribed blasts |
| Short blast | About one second |
| Prolonged blast | Four to six seconds |
No "medium" blast exists. Horn/siren/whistle are not separate legal categories — the Rules use whistle as the umbrella term.
Rule 33 — Equipment by Length
| Length overall | Minimum equipment |
|---|---|
| ≥ 12 m | Whistle |
| ≥ 20 m | Whistle + bell |
| ≥ 100 m | Whistle + bell + gong (gong distinct from the bell) |
| < 12 m | Some other means of making an efficient sound signal |
The bell supports anchor/aground signals in fog; on ships ≥100 m the gong is sounded aft immediately after the bell. Most Master LT 100 platforms fall in the 12–100 m bands — know your outfit and what Q100 still asks about ships with gongs.
Rule 34 — Vessels In Sight of One Another
Rule 34 maneuvering signals apply only when vessels are in sight (observed visually). Radar paint alone in fog is Rule 35 / Rule 19, not one- and two-short exchange territory.
International — action signals (power-driven underway)
| Blasts | Meaning (action taken or being taken) |
|---|---|
| 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 |
These report what you are doing, not a proposal awaiting consent. Give-way under Rule 15, make a bold starboard turn (Rule 8), and sound one short so the other vessel sees and hears the same story.
Optional light supplements (both systems): one, two, or three all-round white flashes matching the short-blast count.
Inland — intent and agreement (meeting / crossing)
When power-driven vessels are in sight and meeting or crossing within half a mile:
| Blasts | Inland meaning (intent) |
|---|---|
| One short | I intend to leave you on my port side (port-to-port) |
| Two short | I intend to leave you on my starboard side |
| Three short | I am operating astern propulsion (same as International) |
If in agreement, the other vessel sounds the same signal and both effect a safe passing. If she doubts safety, she sounds the danger signal and both take precautionary action until agreement is reached.
Q100 trap of the decade — same one short, different speech:
- International: "I am altering course to starboard."
- Inland: "I intend to leave you on my port side."
Geometry may look similar (port-to-port often means each alters to starboard), but the exam answer is the statutory phrase. Know which book is active from the COLREGS Demarcation Line.
Overtaking — International vs Inland
International (narrow channel/fairway, Rule 9(e)):
| Signal | Meaning |
|---|---|
| Two prolonged + one short | I intend to overtake on your starboard side |
| Two prolonged + two short | I intend to overtake on your port side |
| Agreement | Prolonged–short–prolonged–short |
Inland (power-driven in sight):
| Signal | Meaning |
|---|---|
| One short | I intend to overtake on your starboard side |
| Two short | I intend to overtake on your port side |
| Agreement | Overtaken vessel sounds a similar signal if safe |
| Doubt | Danger signal — do not force the pass |
Do not import International two-prolonged patterns into Inland harbor stems, or Inland one-short overtaking language into pure International narrow-channel stems.
Danger / doubt — Rule 34(d)
If either vessel fails to understand the other or doubts sufficient avoiding action, sound at least five short and rapid blasts immediately (optional matching light: ≥5 short rapid flashes). Not a fog signal; not a bend signal; not a greeting.
Bend / obscured channel — Rule 34(e)
Nearing a bend or channel area where vessels may be obscured: sound one prolonged blast. A vessel within hearing around the bend answers with one prolonged blast. (Ties to Rule 9 alertness.)
Inland leaving a dock
Under Inland Rules, a power-driven vessel leaving a dock or berth sounds one prolonged blast. International Rule 34 has no matching dock-departure mandate — Q100 still tests the Inland fact on NC candidates.
Worked Master scenarios
A — International (seaward of demarcation). Give-way freighter on starboard bow: alter boldly to starboard and sound one short (action). No agreement blast required under International maneuvering logic.
B — Inland harbor within half a mile. Propose port-to-port with one short; taxi answers one short and both execute. Five-plus shorts from the taxi = stop forcing that pass.
C — International narrow-channel overtake. Pass on her starboard side: two prolonged + one short, wait for prolonged-short-prolonged-short, then pass only with sea room for passengers.
Exam Framing for Q100 (90%)
Highest-yield: short ≈ 1 s, prolonged 4–6 s; equipment 12 / 20 / 100 m; International action vs Inland intent + agreement; overtaking sequences differ by book; ≥5 short rapid = danger/doubt; one prolonged = bend; three short = astern in both systems. Answer with the rule's words — distractors swap "intend" and "am altering" on purpose.
Under the International Rules, when vessels are in sight of one another, one short blast on the whistle of a power-driven vessel means:
Under the Inland Rules, power-driven vessels meeting within half a mile exchange one short blast and the other answers with one short blast. What has been established?
As Master of a passenger vessel in a narrow channel under International Rules, you intend to overtake the vessel ahead on her starboard side. Which whistle signal indicates that intention?