1The rule in plain words
In one sentence…
Rule 32 gives names to three sound-signal definitions: the appliance and the two durations you need for COLREG study.
What is a whistle?
It is any sound signaling appliance capable of producing the prescribed blasts and complying with Annex III to these Regulations.
How long is a short blast?
It is a blast of about one second’s duration. The word “about” does not set an exact figure.
How long is a prolonged blast?
It is a blast of from four to six seconds’ duration.
2Listen to it
Play each signal and listen: this is how it sounds at sea.
3Key points
- 1.
Whistle = sound signaling appliance complying with Annex III.
- 2.
Short blast → about one second’s duration.
- 3.
Prolonged blast → from four to six seconds’ duration.
- 4.
Rule 32 separates the appliance, short blast and prolonged blast.
4Frequent mistakes
Wrong: "Any device that makes a noise is a whistle."
Right: It must produce prescribed blasts and comply with Annex III.
Wrong: "A short blast lasts exactly one second."
Right: The duration is about one second, not an exact fixed time.
Wrong: "A prolonged blast always lasts exactly six seconds."
Right: Its duration is from four to six seconds.
5Exam keys & interpretation
Exam keys
Only the short blast is "about" one second; the prolonged blast is simply four to six seconds.
"Annex III" identifies the appliance specifications; making any sound is not enough.
Separate short (about 1 s) from prolonged (4–6 s); one changed word can reverse the answer.
How to read it
Read "about" as written: COLREG gives a time reference, not an exact duration.
Apply the whistle definition with both checks: prescribed blasts and compliance with Annex III to these Regulations.
6Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
(a) The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations.
(b) The term short blast means a blast of about one second’s duration.
(c) The term prolonged blast means a blast of from four to six seconds’ duration.7Test your knowledge
What can be considered a whistle under Rule 32?
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