Sound Signals in Sight: Maneuvering and Warning (Rule 34)

Introduction

Sound signals are the auditory component of the Navigation Rules' communication system. While lights and shapes communicate a vessel's status and identity, sound signals communicate intent, action, and warning during maneuvering situations. Rule 34 governs sound signals for vessels in sight of one another, while Rule 35 (covered in the next lesson) governs signals in restricted visibility.

Understanding sound signals is complicated by one of the most significant differences between International and Inland Rules: the fundamental meaning of the signals themselves. This lesson clarifies these differences and provides the complete framework for proper sound signal use.

Definitions and Equipment (Rules 32, 33)

Before discussing the signals themselves, understanding the equipment requirements is essential.

Whistle Requirements (Rule 33)

Every vessel must be provided with a whistle (the regulatory term for the sound-producing device, whether it's actually a whistle, horn, or electronic device).

Vessels 12 meters (39.4 ft) or more in length: Must have a whistle capable of producing the required frequency range and audible range for the vessel's size. Specific requirements in 33 CFR 86 (Annex III) mandate:

• Vessels 20-75m: Whistle audible at least 1 nautical mile
• Vessels 75-200m: Whistle audible at least 2 nautical miles
• Vessels ≥200m: Whistle audible at least 2 nautical miles (higher frequency requirements)

Vessels under 12 meters: Must have "some means of making an efficient sound signal." This can be:

• Handheld air horn (most common for recreational vessels)
• Mouth whistle
• Electronic horn
• Any device capable of producing a blast audible for at least 0.5 nautical miles

Blast Definitions:

• Short blast: 1 second duration (written as • or "dot")
• Prolonged blast: 4-6 seconds duration (written as - or "dash")

Bell and Gong Requirements (Rule 33)

Vessels 12 meters or more: Must carry a bell

Vessels 100 meters or more: Must carry a bell forward AND a gong aft (different tone)

The bell must be at least 300mm (11.8 inches) in diameter for vessels 20m and over. These are used for fog signals and anchor signals, covered in Lesson 7.

The Great Divide: Inland "Intent" vs. International "Action"

This is the most critical concept in understanding sound signals. The fundamental meaning of maneuvering whistle signals is completely different depending on whether you are operating in Inland or International waters.

International Rules (International Waters)

In International waters, whistle signals are signals of action. They mean "I AM altering my course" or "I AM doing this maneuver."

One short blast (•) = "I am altering my course to starboard" Two short blasts (• •) = "I am altering my course to port" Three short blasts (• • •) = "I am operating astern propulsion" (going in reverse)

These are notifications, not requests. The vessel sounds the signal AS it maneuvers. No reply is required or expected. The signal simply notifies nearby vessels of the action being taken.

Inland Rules (US Waters)

In Inland waters, whistle signals are signals of intent. They mean "I INTEND to do this" and require agreement from the other vessel.

One short blast (•) = "I intend to leave you on my port side" (port-to-port passing) Two short blasts (• •) = "I intend to leave you on my starboard side" (starboard-to-starboard passing)

The other vessel must reply with the same signal to indicate agreement. Only after hearing the agreement signal may the first vessel proceed with the maneuver.

If no agreement: If the other vessel does not agree with the proposed maneuver, it must sound the danger signal (5 or more short blasts) and NOT proceed with the maneuver.

Why This Difference Exists

International waters involve primarily large commercial vessels with predictable, slow-developing situations. Vessels maneuver according to the Navigation Rules (crossing, meeting, overtaking), and the whistle signal simply confirms what vessel is doing.

Inland waters (rivers, harbors, channels) involve more complex situations with currents, confined waters, and mixed traffic. The "proposal and agreement" system allows vessels to negotiate safe passing arrangements that may differ from standard rules due to local conditions.

Critical Safety Point: Mariners transitioning from Inland to International waters (or vice versa) across the COLREGS Demarcation Line must immediately shift their understanding of whistle signal meaning. A failure to understand this difference has caused numerous collisions.

Maneuvering Signals in Meeting and Crossing Situations

Head-On Situation (Rule 14 + Rule 34)

International: Each vessel sounds one short blast (•) AS it alters course to starboard. No agreement required.

Inland: First vessel proposes one short blast (•) meaning "I intend port-to-port passing." Other vessel replies with one short blast (•) to agree. Both vessels then alter course to starboard.

Crossing Situation (Rule 15 + Rule 34)

International: The give-way vessel sounds the appropriate signal as it maneuvers:

• One short blast (•) if altering to starboard
• Two short blasts (• •) if altering to port
• No signal from stand-on vessel unless it takes action under Rule 17(b)

Inland: The give-way vessel proposes its maneuver (one or two blasts). The stand-on vessel must reply with the same signal to agree before the give-way vessel proceeds.

Overtaking Signals (Rule 13 + Rule 34)

Overtaking signals are specifically addressed in Rule 34(c) and have additional complexity in Inland waters.

International Rules - Overtaking

In International waters, overtaking signals follow the standard "action" format:

• One short blast (•) = "I am altering course to starboard" (to pass)
• Two short blasts (• •) = "I am altering course to port" (to pass)

The vessel being overtaken has no obligation to signal or agree-the overtaking vessel bears full responsibility under Rule 13.

Inland Rules - Overtaking (The Complex Case)

In Inland waters, Rule 34(c) establishes specific overtaking signals that differ from standard maneuvering signals:

Overtaking on starboard side of vessel ahead: Overtaking vessel sounds: 1 prolonged + 1 short (- •)

Overtaking on port side of vessel ahead: Overtaking vessel sounds: 1 prolonged + 2 short (- • •)

The vessel being overtaken must reply:

• Same signal (- • or - • •) = Agreement, proceed with overtaking
• Five or more short rapid blasts = Danger signal, do NOT overtake

In narrow channels (Rule 9 + Rule 34), this agreement is mandatory. The overtaking vessel must not proceed unless the vessel ahead signals agreement.

Mnemonic:

• Inland overtaking signals always start with one prolonged blast
• Add one short for starboard side pass, two short for port side pass

Other Inland-Specific Signals

The "Bend" Signal (Rule 34e - Inland Only)

A vessel nearing a bend or area of a channel or fairway where other vessels may be obscured shall sound:

One prolonged blast (-)

This "I'm coming around a blind bend" signal alerts any vessel on the other side of the bend to your approach. If a vessel on the other side of the bend hears this signal, it shall answer with one prolonged blast.

Not required in International waters, but is permitted.

Leaving Dock Signal (Rule 34g - Inland Only)

A power-driven vessel leaving a dock or berth shall sound:

One prolonged blast (-)

This alerts nearby traffic that the vessel is getting underway from a stopped position.

The "No" Button: The Danger Signal (Rule 34d)

This is the universal emergency signal that applies in both International and Inland waters, in sight or not in sight.

Five or more short, rapid blasts (• • • • • +)

Meaning: "I do not understand your intentions" OR "Your indicated maneuver is dangerous" OR "I am taking emergency action"

When to use the danger signal:

1. In Inland waters: When another vessel proposes a maneuver you don't agree with (instead of agreeing signal)
2. In any waters: When you're unsure what another vessel is doing
3. Emergency situation: When taking emergency action to avoid collision
4. Doubt about passing agreement: When vessels' intentions seem unclear or unsafe

Legal Effect: Sounding the danger signal immediately nullifies any proposed maneuvering agreement. Both vessels must stop, reassess, communicate via VHF if possible, and establish clear, safe intentions before proceeding.

Important: The danger signal is NOT a substitute for taking action. If you sound the danger signal, you must also be taking or prepared to take emergency action to avoid collision (Rule 2 - Responsibility, and Rule 8 - Action to Avoid Collision).

Other "In-Sight" Signals

Power-Driven Vessel Towing (Rule 34f - Inland Only)

When a power-driven vessel is pushing ahead or towing alongside (Inland waters only), it may, when in a narrow channel and being overtaken, sound:

One short, one prolonged, one short, one short (• - • •)

This is the attention signal indicating "I am a towing vessel and I have doubts about your overtaking maneuver."

Practical Application

Scenario 1: Inland - Meeting Head-On

You and another vessel are meeting head-on in an Inland channel.

• You sound: One short blast (•) - "I propose port-to-port passing"
• Wait for reply
• Other vessel sounds: One short blast (•) - "I agree"
• Both vessels alter course to starboard and pass port-to-port
• No further signals unless changing maneuver

Scenario 2: Inland - Overtaking

You are overtaking a slower vessel in an Inland narrow channel and want to pass on its starboard side.

• You sound: One prolonged + one short (- •) - "I intend to overtake on your starboard side"
• Wait for reply
• Vessel ahead sounds: One prolonged + one short (- •) - "Agreement, I will hold my course"
• You proceed with overtaking on its starboard side

Scenario 3: Danger Signal Required

You're in an Inland crossing situation. The give-way vessel proposes two short blasts (• •) indicating it wants to alter to port and pass starboard-to-starboard. However, there's a submerged hazard on that side that makes this unsafe.

• You sound: Five short rapid blasts (• • • • •) - Danger signal
• You do NOT sound agreement
• Both vessels slow/stop
• You communicate via VHF to explain the hazard
• Agree on alternative plan (likely port-to-port passing with one short blast)

Summary

Sound signals for vessels in sight differ fundamentally between International (action signals) and Inland (intent signals). In International waters, one short means "I AM altering to starboard." In Inland waters, one short means "I INTEND to leave you on my port side" and requires agreement.

Overtaking signals in Inland waters use prolonged + short blast(s). Inland-only signals include the bend signal and leaving dock signal (both one prolonged blast).

The danger signal (five or more short rapid blasts) applies universally and means disagreement, confusion, or emergency action. Always respond appropriately to the danger signal by stopping, reassessing, and communicating before proceeding.

Understanding these signals and their proper use is essential for safe navigation in all waters.

Key Takeaways

• International signals mean "I AM doing this" (action); Inland signals mean "I INTEND to do this" (intent requiring agreement)
• One short = alter to starboard (Int'l) or port-to-port passing (Inland)
• Two short = alter to port (Int'l) or starboard-to-starboard passing (Inland)
• Inland overtaking uses prolonged + short(s): - • for starboard, - • • for port
• Bend signal (Inland only): one prolonged blast when approaching blind bend
• Danger signal: five or more short rapid blasts = disagreement/emergency
• Agreement required in Inland waters before proceeding with proposed maneuver
• Crossing COLREGS Demarcation Line requires immediate shift in signal interpretation