Sound Signal Definitions — What Counts as a Short Blast and a Prolonged Blast

What the rule requires

The two durations

There are exactly two blast lengths in the Rules. A short blast is a blast of about 1 second's duration, and a prolonged blast is a blast of from 4 to 6 seconds' duration 33 CFR §83.32. The International text says the same thing in the same three paragraphs COLREGs Rule 32, so a duration question is answered the same way whether the stem is labelled International, Inland, or both.

Nothing derives these numbers. Four-to-six is a drafting choice, not a computation, and the exam tests it as raw recall. The distractor that catches people is a plausible middle value such as two-to-four seconds, so fix the bracket as a bracket: 4 low, 6 high, nothing in between counts as anything else.

There is no "long blast" in the Rules. Mariners say it in the wheelhouse and the phrase appears in plenty of informal writing, but the defined terms are short and prolonged, and a question that offers "one long blast" as an option is offering you a term the regulation does not use.

You sound what you take to be a prolonged blast and count "one-thousand-one, one-thousand-two, one-thousand-three" while your hand is on the lanyard. Compliant?

No. Three seconds falls short of the 4 to 6 seconds a prolonged blast requires . It is also too long to be a short blast, so what you produced is not a defined signal at all. Count to at least four, and let six be your ceiling so successive blasts in a two-blast signal stay distinguishable.

Which unit belongs to which situation

Short blasts are the vocabulary of vessels in sight of one another. Under the International rule, a power-driven vessel underway indicates a maneuver with one short blast for altering course to starboard, two short for altering course to port, and three short for operating astern propulsion COLREGs Rule 34. The trigger clause at the head of that rule is "when vessels are in sight of one another" — visual contact is the switch.

Prolonged blasts are the vocabulary of restricted visibility. In or near an area of restricted visibility, by day or night, a power-driven vessel making way sounds one prolonged blast at intervals of not more than 2 minutes; underway but stopped and making no way through the water, two prolonged blasts in succession with an interval of about 2 seconds between them 33 CFR §83.35. Vessels not under command, restricted in their ability to maneuver, sailing, engaged in fishing, or engaged in towing or pushing sound one prolonged followed by two short, again at not more than 2 minutes. A manned vessel being towed — the last one, if there is more than one — sounds one prolonged followed by three short.

Both trigger conditions can be true at once, which is why the two sets are not alternatives so much as different jobs. Fog thick enough to hide a ship at two miles still leaves you in sight of the tug crossing a hundred yards ahead.

Where the sources diverge on who sounds the one-prolonged-two-short signal, they diverge by class, not by count. The International rule adds a vessel constrained by her draft to that group, and puts a vessel engaged in fishing at anchor and a vessel restricted in her ability to maneuver carrying out work at anchor onto the same signal instead of the anchor signal COLREGs Rule 35. The Inland rule has no constrained-by-draft class in the list, and instead builds the anchored case into the class itself: restricted in her ability to maneuver "whether underway or at anchor", and engaged in fishing "whether underway or at anchor" . Same three blasts either way.

What "whistle" means

The word whistle means any sound signaling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III , Annex III being 33 CFR part 86 on the Inland side. The definition is functional. A device qualifies because it can produce the prescribed blasts to specification, not because of what it is called on the invoice — and a horn that cannot hold a note for four seconds cannot produce a prolonged blast, so it is not a whistle for the purposes of these Rules.

The equipment that has to be aboard

Thresholds are by length, and the Inland and International texts are word-for-word here 33 CFR §83.33, COLREGs Rule 33:

12 metres or more — a whistle.
20 metres or more — a bell in addition to the whistle.
100 metres or more — a gong in addition, of a tone and sound that cannot be confused with the bell.
Less than 12 metres — not obliged to carry any of the above, but if she does not, she shall be provided with some other means of making an efficient sound signal.

Bell or gong or both may be replaced by other equipment having the same sound characteristics, on one condition: manual sounding of the prescribed signals shall always be possible. The Annex III specifications back that up — a bell or gong shall produce a sound pressure level of not less than 110 dB at 1 metre, be made of corrosion-resistant material, have a mouth of not less than 300 mm diameter on vessels of 20 metres or more, and carry a striker of not less than 3 percent of the mass of the bell; a power-driven striker is recommended where practicable but manual operation shall be possible 33 CFR §86.02.

The 100 GT candidate who will operate a 19-metre vessel should still learn the 20-metre bell threshold cold, because the exam asks it from the other direction: given a length, name the required outfit.

Telling it apart

The criterion is elapsed time, and three of the sounds in this topic sit within a few seconds of each other. Learn them against the clock, not against a description.

Short blast — about 1 second. Filed wrong most often when a candidate hears "two short blasts" in a fog scenario and accepts it; two shorts is a maneuvering signal between vessels in sight of one another, and the fog equivalent for a vessel stopped and making no way is two prolonged COLREGs Rule 34.
Prolonged blast — 4 to 6 seconds. Two of them in succession, separated by about 2 seconds, makes the stopped-and-making-no-way signal run 10 to 14 seconds end to end 33 CFR §83.35. If your version of that signal is over in three seconds, you have sounded neither.
Rapid ringing of the bell — about 5 seconds, and not a blast at all. It is the anchor signal, and its repetition interval is not more than 1 minute, against the 2 minutes that governs every underway whistle signal in the rule. On a vessel of 100 metres or more the bell is rung forward and the gong immediately after, rapidly for about 5 seconds, aft.
Three separate and distinct strokes on the bell — the aground marker, given immediately before and immediately after the rapid ringing, in addition to the anchor bell signal and, where required, the gong.

One further sound belongs to neither list: a vessel at anchor may sound one short, one prolonged and one short to warn an approaching vessel of her position and the possibility of collision, and a pilot vessel engaged on pilotage duty may sound an identity signal of four short blasts. Both are permissive under the Inland rule, and a question that says a vessel "shall" sound either one is wrong on the verb.

In fog you hear a bell rung rapidly for about five seconds, then nothing for roughly a minute, then the same again. What is she, and what is she not?

A vessel at anchor, sounding the signal required at intervals of not more than 1 minute . She is not aground: a vessel aground gives three separate and distinct strokes on the bell immediately before and after the rapid ringing, and you heard no strokes. The 5-second ring is close to a prolonged blast in length, which is exactly why it must be identified by instrument and interval rather than by duration alone.

Working a question

You are operating a 14-metre uninspected passenger vessel on Inland waters. Visibility closes to under 200 yards. You take the way off her and lie stopped, engines running, not anchored. What do you sound, and how often?

Fix the regime. Inland waters puts you in 33 CFR §83.35 rather than the International text. On this particular signal the two agree, but establish the regime before you read the paragraph, because on the fishing-at-anchor and constrained-by-draft cases they do not.
Fix your status. You are underway — not made fast, not aground, not anchored — but stopped and making no way through the water. That is paragraph (b), not paragraph (a).
Read the signal off the rule. Two prolonged blasts in succession, with an interval of about 2 seconds between them 33 CFR §83.35.
Convert to seconds. Each prolonged blast is 4 to 6 seconds 33 CFR §83.32. Call it five, two apart, five: about twelve seconds of work each time.
Set the interval. Not more than 2 minutes between signals. Not more than — sounding it every 90 seconds complies, every 150 does not.
Confirm you have the gear. At 14 metres you are 12 metres or more, so a whistle is required; you are under 20 metres, so no bell is required 33 CFR §83.33.
Extend the case. Anchor in that same fog and the anchor signal is a bell rung rapidly for about 5 seconds at intervals of not more than 1 minute — but a vessel of 12 metres or more and less than 20 metres is not obliged to give it. If she does not, she shall make some other efficient sound signal at intervals of not more than 2 minutes. Anchored in a special anchorage area designated by the Coast Guard, a vessel of less than 20 metres is not required to sound the anchor signal at all.

Step 7 is where the interval changes under your feet: the prescribed anchor signal runs on 1 minute, the substitute you are allowed instead runs on 2.

Where candidates lose the point

Picking "2 to 4 seconds" for a prolonged blast. It reads like a reasonable middle value and it is wrong; the bracket is 4 to 6 seconds 33 CFR §83.32. Nothing in the rule justifies interpolating, so memorise the endpoints.

Answering a fog question with short blasts. A candidate who has just studied maneuvering signals sees "one prolonged followed by two short" and remembers only the "two short", then reaches for a course-change meaning. Course-change signals require that vessels be in sight of one another COLREGs Rule 34; the restricted-visibility signals identify what kind of vessel is out there, not what she intends to do.

Treating a vessel under 12 metres as exempt from making any noise. She is relieved of carrying the whistle, bell and gong, not of being audible: she shall be provided with some other means of making an efficient sound signal 33 CFR §83.33, and in restricted visibility, if she is not giving the prescribed signals, she shall make some other efficient sound signal at intervals of not more than 2 minutes 33 CFR §83.35.

Assuming an automatic bell striker satisfies the requirement on its own. A power-driven striker is recommended where practicable, and manual operation shall still be possible 33 CFR §86.02 — the same condition attached to any substitute for the bell or gong . An inspector who cannot ring it by hand has found a deficiency.

Reading "whistle" as a description of hardware. The definition turns on capability and Annex III compliance , which is why a canister air horn that will not sustain a four-second note fails the definition regardless of how loud it is.

Answering the flash timing from the blast timing. Where light signals supplement the whistle, each flash is about 1 second, the interval between flashes about 1 second, and the interval between successive signals not less than 10 seconds, from an all-round white light visible at a minimum range of 5 miles . The one-second unit carries across from the short blast; the 10-second gap and the 5-mile range do not appear anywhere in Rule 32 and have to be learned on their own.

Check yourself

(Both International & Inland) A blast of about one second's duration is called what, and a blast of four to six seconds?

A short blast and a prolonged blast respectively 33 CFR §83.32, COLREGs Rule 32. Reject any option using "long blast" — the Rules define no such term.

(Both International & Inland) You are underway in fog on a power-driven vessel, dead in the water with engines stopped. Which signal, and at what maximum interval?

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. Two short blasts is the trap; that combination belongs to maneuvering signals between vessels in sight of one another.

(Both International & Inland) Your vessel is 22 metres in length. What sound signaling appliances must be provided, and what must the bell meet?

A whistle and, because she is 20 metres or more, a bell in addition; a gong is not required until 100 metres 33 CFR §83.33. The bell must produce not less than 110 dB at 1 metre, be of corrosion-resistant material, and have a mouth of not less than 300 mm at that length, with a striker of at least 3 percent of the bell's mass 33 CFR §86.02.

(Inland Only) You are at anchor in fog in a 15-metre vessel with no bell aboard. What are you required to do?

You are not obliged to give the bell signal, but you must make some other efficient sound signal at intervals of not more than 2 minutes . Note the interval: the bell signal itself runs at not more than 1 minute, the substitute at not more than 2. If you are anchored in a special anchorage area designated by the Coast Guard, a vessel of less than 20 metres is not required to sound the anchor signal.

(International Only) In restricted visibility, which vessel sounds one prolonged followed by two short under the International rule but is not named in the Inland list for that signal?

A vessel constrained by her draft COLREGs Rule 35. The Inland list covers not under command, restricted in ability to maneuver whether underway or at anchor, sailing, engaged in fishing whether underway or at anchor, and towing or pushing .

(Both International & Inland) A hand-held air horn aboard your 13-metre vessel will produce a maximum blast of about two seconds. Does it satisfy the whistle requirement?

No. A whistle is an appliance capable of producing the prescribed blasts and complying with Annex III , and a device that cannot hold a note for 4 to 6 seconds cannot produce a prolonged blast. At 13 metres you are 12 metres or more, so a whistle is required equipment — the under-12-metre allowance for "some other means of making an efficient sound signal" is not available to you.