What is Rule 34 Maneuvering and warning signals?

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: one short blast to mean “I intend to leave you on my port side”; two short blasts to mean “I intend to leave you on my starboard side”; and 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 danger signal specified in paragraph (d) of this Rule and each vessel shall take appropriate precautionary action until a safe passing agreement is made.

(b) Light signals

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: one flash to mean “I intend to leave you on my port side”; two flashes to mean “I intend to leave you on my starboard side”; 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.

(c) Overtaking situations

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: one short blast to mean “I intend to overtake you on your starboard side”; 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 danger signal prescribed in paragraph (d).

(d) Doubts or failure to understand signals

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. This signal may be supplemented by a light signal of at least five short and rapid flashes.

(e) Vessels in areas of obscured visibility due to intervening obstructions

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) Use of one whistle only on a vessel

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) Power-driven vessels leaving dock or berth

When a power-driven vessel is leaving a dock or berth, she shall sound one prolonged blast.

(h) Agreement between vessels using radiotelephone

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 et seq.), 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.

(Pub. L. 96–591, §2, Dec. 24, 1980, 94 Stat. 3430; Pub. L. 104–324, title VII, §701(6), Oct. 19, 1996, 110 Stat. 3933.)

Pub. L. 108–293, title III, §303(a), (c), Aug. 9, 2004, 118 Stat. 1042, provided that this section is repealed effective on the effective date of final regulations prescribed by the Secretary of the Department in which the Coast Guard is operating under section 2071 of this title 

Section 2071 — Inland navigation rulesThe Secretary of the Department in which the Coast Guard is operating may issue inland navigation regulations applicable to all vessels upon the inland waters of the United States and technical annexes that are as consistent as possible with the respective annexes to the International Regulations.
(Pub. L. 96–591, §3, Dec. 24, 1980, 94 Stat. 3433; Pub. L. 108–293, title III, §303(b), Aug. 9, 2004, 118 Stat. 1042.)
References in Text
The International Regulations, referred to in text, are the International Regulations for Preventing Collisions at Sea, 1972, which are maintained and published by the United States Coast Guard, U.S. Department of Homeland Security, in the publication Navigation Rules, which is available for sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. See International Regulations for Preventing Collisions at Sea, 1972 note under section 1602 of this title 

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These Rules, referred to in par. (a), are the Inland Navigational Rules which are classified to this subchapter.

Annex I to these Rules, referred to in par. (b)(iii), is to be established by the Secretary under section 2071 of this title 

The Vessel Bridge-to-Bridge Radiotelephone Act, referred to in par. (h), is Pub. L. 92–63, Aug. 4, 1971, 85 Stat. 164, as amended, which is classified generally to chapter 24 (§1201 et seq.) of this title 

Chapter 24 — VESSEL BRIDGE-TO-BRIDGE COMMUNICATION
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Section was enacted as part of section 2 of Pub. L. 96–591 which enacted the Inland Navigational Rules which comprise this subchapter.

1996—Par. (h). Pub. L. 104–324 amended par. (h) generally. Prior to amendment, par. (h) read as follows: “A vessel that reaches agreement with another vessel in a meeting, crossing, or overtaking situation by using the radiotelephone as prescribed by the Bridge-to-Bridge Radiotelephone Act (85 Stat. 165; 33 U.S.C. 1207), 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.”