Rule 32 — Sound Signal Definitions

TL;DR — Under Inland Rule 32, a "short blast" lasts about 1 second and a "prolonged blast" lasts 4 to 6 seconds; a "whistle" is any sound signaling appliance capable of producing those prescribed blasts in compliance with Annex III specifications. 33 CFR §83.32

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What the Rule Says

Rule 32 establishes three foundational definitions that underpin every sound signal requirement in the Inland Navigation Rules. Without a precise understanding of these three terms, no other sound signal rule can be correctly interpreted or applied.

Whistle 33 CFR §83.32(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 (33 CFR part 86). 33 CFR §83.32 Note carefully what this definition does and does not say: it does not restrict the term to a traditional steam whistle or air horn of any particular design. The appliance qualifies as a "whistle" if — and only if — it can produce the required blasts and meets the Annex III technical specifications. 33 CFR §83.32

Short Blast 33 CFR §83.32(b)

A "short blast" means a blast of about 1 second's duration. 33 CFR §83.32 The word "about" is deliberate — the Rules do not demand exactly 1.000 seconds, but the blast must be recognizably distinct from a prolonged blast. In practice, mariners and examiners treat 1 second as the standard.

Prolonged Blast 33 CFR §83.32(c)

A "prolonged blast" means a blast of from 4 to 6 seconds' duration. 33 CFR §83.32 This is a range, not a single value. Any blast within that 4-to-6-second window satisfies the definition. A blast shorter than 4 seconds is not a prolonged blast; a blast longer than 6 seconds is also non-compliant.

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Why It Matters on the Exam

These three definitions are the building blocks for every sound signal question on the OUPV and Master 100 GT written examination. Examiners routinely test them in two ways: directly (asking for the definition itself) and indirectly (embedding the definitions inside questions about maneuvering signals, restricted visibility signals, or equipment requirements). You must know the numbers cold.

Connection to Rule 34 — Maneuvering and Warning Signals

Rule 34 prescribes signals composed entirely of short blasts. 33 CFR §83.34 For example:

• One short blast: "I intend to leave you on my port side." 33 CFR §83.34(a)(i)(1)
• Two short blasts: "I intend to leave you on my starboard side." 33 CFR §83.34(a)(i)(2)
• Three short blasts: "I am operating astern propulsion." 33 CFR §83.34(a)(i)(3)
• Five or more short and rapid blasts: the doubt or danger signal. 33 CFR §83.34(d)
• One prolonged blast: signal when leaving a dock or berth, or when approaching a bend. 33 CFR §83.34(e)(g)

Every one of those signals depends on the Rule 32 definitions. If you do not know that a short blast is about 1 second, you cannot correctly identify or produce a maneuvering signal. 33 CFR §83.32

Connection to Rule 35 — Restricted Visibility Signals

Rule 35 signals are built from combinations of prolonged and short blasts. 33 CFR §83.35 For example:

• A power-driven vessel making way: one prolonged blast at intervals of not more than 2 minutes. 33 CFR §83.35(a)
• A power-driven vessel underway but stopped and making no way: two prolonged blasts in succession with an interval of about 2 seconds between them, at intervals of not more than 2 minutes. 33 CFR §83.35(b)
• A vessel not under command, a vessel restricted in her ability to maneuver, a sailing vessel, a vessel engaged in fishing, or a vessel towing or pushing: one prolonged blast followed by two short blasts, at intervals of not more than 2 minutes. 33 CFR §83.35(c)
• A manned vessel being towed (or the last vessel of a tow): one prolonged blast followed by three short blasts, at intervals of not more than 2 minutes. 33 CFR §83.35(e)

Recognizing these signals aurally — or identifying them on a written exam — requires instant recall of the Rule 32 durations. 33 CFR §83.32

Connection to Rule 33 — Equipment Requirements

Rule 33 specifies which vessels must carry a whistle, bell, and gong. 33 CFR §83.33 The term "whistle" in Rule 33 carries the exact meaning established in Rule 32: an appliance meeting Annex III specifications. 33 CFR §83.32 33 CFR §83.33 Specifically:

• A vessel of 12 meters or more in length shall be provided with a whistle. 33 CFR §83.33(a)
• A vessel of 20 meters or more in length shall be provided with a bell in addition to a whistle. 33 CFR §83.33(a)
• A vessel of 100 meters or more in length shall, in addition, be provided with a gong whose tone cannot be confused with that of the bell. 33 CFR §83.33(a)
• A vessel of less than 12 meters in length is not obliged to carry the prescribed appliances but must carry some other means of making an efficient sound signal if she does not. 33 CFR §83.33(b)

The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the prescribed signals shall always be possible. 33 CFR §83.33(a)

The Annex III Compliance Requirement

The Rule 32 definition of "whistle" explicitly ties the appliance to Annex III compliance (33 CFR part 86). 33 CFR §83.32 This is not merely a technical footnote — exam questions sometimes ask whether a particular device qualifies as a "whistle" under the Rules. The answer always turns on two criteria: (1) can it produce the prescribed blasts, and (2) does it comply with Annex III. 33 CFR §83.32 An appliance that makes noise but does not meet those criteria is not a "whistle" within the meaning of the Rules.

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Common Pitfalls

Confusing the duration ranges

The most common exam error is inverting the durations — stating that a short blast is 4 to 6 seconds or that a prolonged blast is about 1 second. Drill the numbers until they are automatic: short = about 1 second; prolonged = 4 to 6 seconds. 33 CFR §83.32

Treating "prolonged blast" as a fixed value

Candidates sometimes write "5 seconds" as the definition of a prolonged blast, because 5 seconds is the midpoint of the range. The rule states 4 to 6 seconds. 33 CFR §83.32 An exam question that offers "5 seconds" as one answer choice and "4 to 6 seconds" as another is testing precisely this distinction. Select the range.

Assuming "whistle" means only a traditional steam or air whistle

Rule 32 defines "whistle" functionally, not by construction type. Any compliant sound signaling appliance qualifies. 33 CFR §83.32 Do not eliminate an answer choice simply because the appliance described is electronic or of unconventional design, provided it meets the Annex III specifications.

Misapplying Rule 32 definitions to bell and gong signals

Rule 32 defines "whistle," "short blast," and "prolonged blast." 33 CFR §83.32 Bell and gong signals — such as the anchor signal (rapid ringing for about 5 seconds at intervals of not more than 1 minute) — are not described in terms of short or prolonged blasts. 33 CFR §83.35(g) Do not apply the 1-second or 4-to-6-second durations to bell or gong signals.

Overlooking the "about" qualifier on short blast duration

The rule says "about 1 second," not "exactly 1 second." 33 CFR §83.32 On the exam, if a question asks for the duration of a short blast, the correct answer is "about 1 second" — not "1 second" stated as an absolute. This distinction rarely changes the answer on a multiple-choice exam, but it matters for written-response questions and for practical application.

Confusing the Rule 35 two-prolonged-blast signal with the Rule 34 departure signal

A power-driven vessel underway but stopped and making no way sounds two prolonged blasts in restricted visibility. 33 CFR §83.35(b) A power-driven vessel leaving a dock or berth sounds one prolonged blast. 33 CFR §83.34(g) Both signals use prolonged blasts, but the number and context differ entirely. Knowing the Rule 32 definition of "prolonged blast" is necessary but not sufficient — you must also know which rule governs which situation.

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Quick Check

Q1 — What is the duration of a short blast under Inland Rule 32?

A short blast means a blast of about 1 second's duration. 33 CFR §83.32(b)

Q2 — What is the duration range for a prolonged blast under Inland Rule 32?

A prolonged blast means a blast of from 4 to 6 seconds' duration. 33 CFR §83.32(c)

Q3 — How does Inland Rule 32 define the word "whistle"?

"Whistle" means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Rules (33 CFR part 86). 33 CFR §83.32(a)

Q4 — A vessel of 20 meters in length is required to carry which sound signaling appliances?

A vessel of 20 meters or more in length shall be provided with a whistle and a bell. Both must comply with Annex III specifications (33 CFR part 86). 33 CFR §83.33(a)

Q5 — In restricted visibility, what signal does a power-driven vessel underway but stopped and making no way sound, and how often?

Two prolonged blasts in succession, with an interval of about 2 seconds between them, at intervals of not more than 2 minutes. 33 CFR §83.35(b) Each prolonged blast must be 4 to 6 seconds in duration. 33 CFR §83.32(c)

Q6 — A vessel not under command is underway in restricted visibility. What sound signal does she make and at what interval?

One prolonged blast followed by two short blasts, at intervals of not more than 2 minutes. 33 CFR §83.35(c) The prolonged blast is 4 to 6 seconds; each short blast is about 1 second. 33 CFR §83.32

Q7 — Under Inland Rule 34, what does one short blast mean when two power-driven vessels are meeting or crossing within half a mile of each other?

One short blast means "I intend to leave you on my port side." 33 CFR §83.34(a)(i)(1) That blast must be about 1 second in duration. 33 CFR §83.32(b)

Q8 — A vessel of less than 12 meters in length does not carry a whistle. What is she required to have?

She shall be provided with some other means of making an efficient sound signal. 33 CFR §83.33(b)