What does Rule 34 cover?

Rule 34 covers maneuvering and warning signals. It gives the short-blast codes for course changes, astern propulsion, overtaking in narrow channels, bend or obstruction warnings, and the five-or-more-short-blast danger signal.

What do one, two, and three short blasts mean under COLREGs?

Under COLREGs Rule 34, one short blast means 'I am altering my course to starboard,' two short blasts means 'I am altering my course to port,' and three short blasts means 'I am operating astern propulsion.'

Why is Inland Rule 34 different from COLREGs Rule 34?

Inland Rule 34 treats one- and two-short-blast meeting, crossing, and overtaking signals as intent signals. One short means 'I intend to leave you on my port side'; two short means 'I intend to leave you on my starboard side.' 33 CFR §83.34(a) limits that to power-driven vessels in sight of one another and meeting or crossing within half a mile, and the other vessel must answer with the same signal if it agrees or sound the danger signal if it does not.

What does five short blasts mean?

Five or more short and rapid blasts means danger or doubt. Use it when you do not understand another vessel's intentions or doubt whether enough action is being taken to avoid collision. Under 33 CFR §83.34(d) the whistle signal may be supplemented by a light signal of at least five short and rapid flashes.

How long is a short blast compared with a prolonged blast?

33 CFR §83.32 defines a short blast as a blast of about 1 second's duration and a prolonged blast as a blast of from 4 to 6 seconds' duration. Those two lengths are the whole alphabet of Rule 34: the maneuvering, overtaking, and danger signals are short blasts, while the blind-bend signal and the Inland dock-departure signal are prolonged blasts.

If another boat signals its intention to pass you from astern, what should you do?

Under Inland Rule 34(c), an overtaking power-driven vessel sounds one short blast for 'I intend to overtake you on your starboard side' or two short blasts for 'I intend to overtake you on your port side.' If you agree, sound a similar signal back and let her pass; if you are in doubt, sound at least five short and rapid blasts instead. Under COLREGs the narrow-channel overtaking signal is two prolonged plus one short (starboard side) or two prolonged plus two short (port side), answered by prolonged-short-prolonged-short.

Can you use light signals instead of the whistle under Rule 34?

No — lights supplement the whistle, they do not replace it. 33 CFR §83.34(b) allows one flash for 'I intend to leave you on my port side,' two flashes for 'starboard side,' and three flashes for astern propulsion. Each flash lasts about 1 second, and the light must be an all-round white or yellow light visible for at least 2 miles, synchronized with the whistle and compliant with Annex I (33 CFR part 84).

What sound signal do you make when leaving a dock or approaching a blind bend?

One prolonged blast in both cases, but only one of them is universal. 33 CFR §83.34(e) requires one prolonged blast when nearing a bend or an area of a channel or fairway where other vessels may be obscured, answered with a prolonged blast by any approaching vessel within hearing. 33 CFR §83.34(g) adds an Inland-only signal: a power-driven vessel leaving a dock or berth sounds one prolonged blast.

Inland Rule 34 — Sound Signals of Intent (not Action)

Rule text#

Source

Verbatim 33 CFR §83.34 as published in the Code of Federal Regulations — public domain, retrieved 2026-07-23.

(a)When power-driven vessels are in sight of one another and meeting or crossing at a distance within half a mile of each other, each vessel underway, when maneuvering as authorized or required by these Rules:
(i)Shall indicate that maneuver by the following signals on her whistle:
(1)One short blast to mean “I intend to leave you on my port side”;
(2)Two short blasts to mean “I intend to leave you on my starboard side”; and
(3)Three short blasts to mean “I am operating astern propulsion”.
(ii)Upon hearing the one or two blast signal of the other shall, if in agreement, sound the same whistle signal and take the steps necessary to effect a safe passing. If, however, from any cause, the vessel doubts the safety of the proposed maneuver, she shall sound the signal specified in paragraph (d) of this Rule and each vessel shall take appropriate precautionary action until a safe passing agreement is made.
(b)A vessel may supplement the whistle signals prescribed in paragraph (a) of this Rule by light signals:
(i)These signals shall have the following significance:
(1)One flash to mean “I intend to leave you on my port side”;
(2)Two flashes to mean “I intend to leave you on my starboard side”;
(3)Three flashes to mean “I am operating astern propulsion”;
(ii)The duration of each flash shall be about 1 second; and
(iii)The light used for this signal shall, if fitted, be one all-round white or yellow light, visible at a minimum range of 2 miles, synchronized with the whistle, and shall comply with the provisions of Annex I to these Rules (33 CFR part 84).
(c)When in sight of one another:
(i)A power-driven vessel intending to overtake another power-driven vessel shall indicate her intention by the following signals on her whistle:
(1)One short blast to mean “I intend to overtake you on your starboard side”;
(2)Two short blasts to mean “I intend to overtake you on your port side”; and
(ii)The power-driven vessel about to be overtaken shall, if in agreement, sound a similar sound signal. If in doubt she shall sound the signal prescribed in paragraph (d) of this Rule.
(d)When vessels in sight of one another are approaching each other and, from any cause, either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle. Such signal may be supplemented by a light signal of at least five short and rapid flashes.
(e)A vessel nearing a bend or an area of a channel or fairway where other vessels may be obscured by an intervening obstruction shall sound one prolonged blast. This signal shall be answered with a prolonged blast by any approaching vessel that may be within hearing around the bend or behind the intervening obstruction.
(f)If whistles are fitted on a vessel at a distance apart of more than 100 meters, one whistle only shall be used for giving maneuvering and warning signals.
(g)When a power-driven vessel is leaving a dock or berth, she shall sound one prolonged blast.
(h)A vessel that reaches agreement with another vessel in a head-on, crossing, or overtaking situation, as for example, by using the radiotelephone as prescribed by the Vessel Bridge-to-Bridge Radiotelephone Act (85 Stat. 164; 33 U.S.C. 1201), is not obliged to sound the whistle signals prescribed by this Rule, but may do so. If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail. [USCG-2012-0102, 79 FR 37912, July 2, 2014, as amended by USCG-2015-0433, 80 FR 44280, July 27, 2015; USCG-2017-1002, 83 FR 3274, Jan. 24, 2018]

Why it shows up on the exam#

Inland Rule 34 has a critical difference: under Inland, the one- and two-short-blast signals are signals of INTENT not action, and 33 CFR §83.34(a) only switches them on between power-driven vessels in sight of one another and meeting or crossing within half a mile. Examiners test that half-mile trigger, the duty to answer with the same signal, and the doubt signal that replaces agreement.

Exam checkpoints#

COLREGs action
1 / 2 / 3 short blasts
In International waters, one short blast means altering course to starboard, two short blasts means altering course to port, and three short blasts means operating astern propulsion.
Inland intent
Leave you port / starboard
Inland Rule 34 uses the same one- and two-short-blast patterns as signals of intent: one short means intending to leave the other vessel on your port side, two short means intending to leave her on your starboard side. 33 CFR §83.34(a) applies them between power-driven vessels in sight of one another and meeting or crossing within half a mile.
Warning signal
5 or more short blasts
Five or more short and rapid blasts is the danger or doubt signal. It belongs on both COLREGs and Inland exams and is the answer when another vessel's intentions are unclear; §83.34(d) lets you supplement it with at least five short and rapid flashes.
Blast length
1 second vs 4–6 seconds
Every Rule 34 signal is built from two lengths defined in 33 CFR §83.32: a short blast is about 1 second, and a prolonged blast is from 4 to 6 seconds. A prolonged blast is never just a drawn-out short blast, and distractors that call it 8 or 10 seconds are wrong.
Blind bend
One prolonged blast
Under §83.34(e) a vessel nearing a bend or a stretch of channel or fairway where other vessels may be hidden by an obstruction sounds one prolonged blast, and any approaching vessel within hearing around the bend must answer with a prolonged blast.
Inland only
Leaving a dock or berth
§83.34(g) requires a power-driven vessel leaving a dock or berth to sound one prolonged blast. COLREGs has no departure signal, so an exam question that rewards 'one prolonged blast' on getting under way is an Inland question.

Inland-specific notes#

Under Inland, 1 short = 'I intend to leave you on my port side'; 2 short = 'I intend to leave you on my starboard side'. The rule bites only between power-driven vessels in sight of one another and meeting or crossing within half a mile: the vessel hearing the signal answers with the same signal if it agrees, or sounds five or more short and rapid blasts if it doubts the maneuver, and both vessels take precautionary action until a safe passing agreement is made. Inland also carries two signals COLREGs does not — one prolonged blast when leaving a dock or berth (§83.34(g)), and an exemption from whistle signals once agreement is reached by radiotelephone under the Vessel Bridge-to-Bridge Radiotelephone Act (§83.34(h)); if no agreement is reached, whistle signals must be exchanged in a timely manner and prevail.

Rule 34 — common exam questions#

What does Rule 34 cover?: Rule 34 covers maneuvering and warning signals. It gives the short-blast codes for course changes, astern propulsion, overtaking in narrow channels, bend or obstruction warnings, and the five-or-more-short-blast danger signal.
What do one, two, and three short blasts mean under COLREGs?: Under COLREGs Rule 34, one short blast means 'I am altering my course to starboard,' two short blasts means 'I am altering my course to port,' and three short blasts means 'I am operating astern propulsion.'
Why is Inland Rule 34 different from COLREGs Rule 34?: Inland Rule 34 treats one- and two-short-blast meeting, crossing, and overtaking signals as intent signals. One short means 'I intend to leave you on my port side'; two short means 'I intend to leave you on my starboard side.' 33 CFR §83.34(a) limits that to power-driven vessels in sight of one another and meeting or crossing within half a mile, and the other vessel must answer with the same signal if it agrees or sound the danger signal if it does not.
What does five short blasts mean?: Five or more short and rapid blasts means danger or doubt. Use it when you do not understand another vessel's intentions or doubt whether enough action is being taken to avoid collision. Under 33 CFR §83.34(d) the whistle signal may be supplemented by a light signal of at least five short and rapid flashes.
How long is a short blast compared with a prolonged blast?: 33 CFR §83.32 defines a short blast as a blast of about 1 second's duration and a prolonged blast as a blast of from 4 to 6 seconds' duration. Those two lengths are the whole alphabet of Rule 34: the maneuvering, overtaking, and danger signals are short blasts, while the blind-bend signal and the Inland dock-departure signal are prolonged blasts.
If another boat signals its intention to pass you from astern, what should you do?: Under Inland Rule 34(c), an overtaking power-driven vessel sounds one short blast for 'I intend to overtake you on your starboard side' or two short blasts for 'I intend to overtake you on your port side.' If you agree, sound a similar signal back and let her pass; if you are in doubt, sound at least five short and rapid blasts instead. Under COLREGs the narrow-channel overtaking signal is two prolonged plus one short (starboard side) or two prolonged plus two short (port side), answered by prolonged-short-prolonged-short.
Can you use light signals instead of the whistle under Rule 34?: No — lights supplement the whistle, they do not replace it. 33 CFR §83.34(b) allows one flash for 'I intend to leave you on my port side,' two flashes for 'starboard side,' and three flashes for astern propulsion. Each flash lasts about 1 second, and the light must be an all-round white or yellow light visible for at least 2 miles, synchronized with the whistle and compliant with Annex I (33 CFR part 84).
Do you still have to sound whistle signals if you agreed to pass on the VHF radio?: Not under the Inland Rules. 33 CFR §83.34(h) says a vessel that reaches agreement with another vessel in a head-on, crossing, or overtaking situation — for example by radiotelephone under the Vessel Bridge-to-Bridge Radiotelephone Act — is not obliged to sound the whistle signals, though she may. If agreement is not reached, whistle signals must be exchanged in a timely manner and they prevail.
What sound signal do you make when leaving a dock or approaching a blind bend?: One prolonged blast in both cases, but only one of them is universal. 33 CFR §83.34(e) requires one prolonged blast when nearing a bend or an area of a channel or fairway where other vessels may be obscured, answered with a prolonged blast by any approaching vessel within hearing. 33 CFR §83.34(g) adds an Inland-only signal: a power-driven vessel leaving a dock or berth sounds one prolonged blast.

Authoritative source#

Source links checked against the current public rule corpus on 2026-07-23.

33 CFR §83.34 — the section this text comes from, with its neighbours.
The Inland Navigation Rules are codified at 33 CFR Part 83 and are public domain. The international COLREGs text is published separately by the IMO.

Practice this rule#

One real exam question on this rule, cited to source. No sign-up.

Under the Inland Rules, a power-driven vessel leaving a dock or berth shall sound ______.

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Maneuvering and Warning Signals