Official rule text as published in the U.S. Coast Guard Navigation Rules
(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 Rules.
(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.
MyCOLREGS explanation
Summary
This rule defines three sound-signal terms used throughout the rules: a whistle is any signaling device that can produce the required blasts and meets the technical spec in Annex III; a short blast lasts about one second; a prolonged blast lasts four to six seconds. Every maneuvering, warning, and fog signal in the rules is built from just these two blast lengths.
Real World Example
Every whistle signal in the rules - danger, overtaking, maneuvering - is built from just two blast lengths, precisely so a skipper under stress can tell them apart instantly over engine noise and wind, without splitting hairs over fractions of a second.
Practice Questions
Q1. You need to sound a prolonged blast under Rule 34 while overtaking in a narrow channel. About how long should you hold it?
A. About one second.
B. Four to six seconds.
C. At least ten seconds.
D. Two to three seconds.
Q2. Your boat's built-in horn only produces one fixed-length "beep" - you can't hold it down to sound a longer blast or release it early for a shorter one. Does that meet Rule 32's definition of a "whistle"?
A. Yes - any sound-producing device aboard automatically counts as a whistle for Rule 32 purposes, regardless of what blast patterns it is or isn't capable of producing.
B. No - Rule 32 defines a whistle as an appliance capable of producing the Rules' prescribed short and prolonged blasts; a fixed single-length horn that can't vary its duration doesn't meet that.
C. Yes, as long as it's audible from at least one mile away, regardless of blast length, since Rule 32 is primarily concerned with a whistle's carrying range rather than its timing.
D. No, but only because it's electric rather than air-powered; Rule 32 requires a mechanically-operated whistle driven by compressed air or a hand pump.
Practice Question Answers
Q1.
B. Four to six seconds Rule 32(c) defines a prolonged blast as a blast of from four to six seconds duration. B overstates the duration well beyond what's required. C and D each undershoot it - Rule 32 specifically defines "prolonged" as four to six seconds, distinct from a short blast's roughly one second.
Q2.
B. Annex III Rule 32(a) requires a whistle to comply with the specifications in Annex III to the Rules. A, C, and D each cite a different annex than the one Rule 32 actually references for the whistle's technical standard - Annex III.