Paragraph (a): "Whistle"
The word "whistle" means any sound signalling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III.
COLREGs trainerPart D: Sound and Light Signals
Rule 32
Definitions
Short blast (~1 s) and prolonged blast (4–6 s).
Wording follows the International Regulations as printed in the US Coast Guard Navigation Rules handbook (2024), with British spelling, and is shortened in places. Download the rules
Read the whole of Rule 32 on one page
Paragraph (a): "Whistle"
The word "whistle" means any sound signalling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III.
Paragraph (b): "Short blast"
The term "short blast" means a blast of about one second’s duration.
Paragraph (c): "Prolonged blast"
The term "prolonged blast" means a blast of from four to six seconds’ duration.
A training aid, not the official text. The COLREGs are an IMO convention, and your national authority publishes the version that applies in its waters. Check the rules themselves before you rely on them at sea. Download the rules.