USCG Sound Signals: The Complete Guide for the Captain's License Exam
Sound signals are tested on every USCG captain's license exam. A licensed captain explains every signal — underway, restricted visibility, anchored, and maneuvering — with the rules that govern them.
The Chartroom Captain
Licensed USCG 100-Ton Near Coastal Master
Why Sound Signals Are Exam-Critical
Sound signals fall under Rules of the Road — the COLREGS section that requires 90% to pass. That means sound signal errors hurt more than errors in other sections. Miss two sound signal questions out of ten COLREGS questions and you've already significantly damaged your passing margin.
The good news: COLREGS sound signals follow a logical system. Once you understand why each signal exists and which rule governs it, memorization becomes much easier. Let's go through the whole system.
The Two Signal Categories You Must Not Confuse
Students constantly mix up two distinct categories of sound signals. Get this distinction first, and everything else follows.
Maneuvering and Warning Signals (Rule 34): Used in sight of one another. These signals communicate what you're doing — turning, backing up, passing in a narrow channel.
Restricted Visibility Signals (Rule 35): Used in or near an area of restricted visibility. These are fog signals — they tell other vessels what type of vessel you are and what you're doing (underway making way, underway not making way, at anchor, aground).
The key difference: Rule 34 signals are when you can see the other vessel. Rule 35 signals are when you can't. Mixing these up is the most common sound signal error on the exam.
Rule 34: Maneuvering Signals (In Sight of One Another)
These apply on international waters. Note: Inland Rules have different maneuvering signals for passing agreements — covered separately below.
Basic Maneuvering Signals (International Rules)
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 (backing)
These are statements of action, not requests for permission. You sound them when you alter course — ideally slightly before or as you make the maneuver.
Danger Signal
Five or more short rapid blasts: Doubt signal / danger signal. Used when you're uncertain about another vessel's intentions or when you believe a collision risk exists. Also used to indicate you do not understand or agree with another vessel's proposed maneuver in a narrow channel.
Inland Rules: Meeting and Passing Signals
Inland Rules (which apply on rivers, lakes, and inland waters inside the demarcation lines) use sound signals differently — they're proposals and agreements, not statements:
One short blast: Proposal to pass port-to-port (I intend to leave you on my port side)
Two short blasts: Proposal to pass starboard-to-starboard
One short blast (response): Agreement
Five or more short blasts: Disagreement or danger
This is a critical exam distinction. On International waters, one short blast means "I'm turning starboard." On Inland waters, one short blast means "I propose to pass you port-to-port." The exam will test whether you know which rules apply in which waters.
These are sounded in or near an area of restricted visibility — fog, rain, haze, or anything that significantly limits sight distance. Vessels must sound these signals at intervals of not more than 2 minutes.
Power-Driven Vessel Underway Making Way
One prolonged blast every 2 minutes
This is the signal most people think of as the basic fog signal. It only applies to a power-driven vessel that is actually moving through the water.
Power-Driven Vessel Underway but Stopped (Not Making Way)
Two prolonged blasts every 2 minutes (with a 2-second silence between them)
This is one of the most commonly missed signals. "Underway" means not at anchor, not moored, not aground — but a vessel can be underway without making way (zero speed through the water). Two prolonged blasts tells other vessels in fog: I'm a power vessel with engines running but I'm not moving.
Sailing Vessels, Fishing Vessels, and Restricted-Maneuverability Vessels
One prolonged blast followed by two short blasts, every 2 minutes
This signal applies to: sailing vessels underway, vessels fishing (engaged in fishing with gear restricting maneuverability), vessels towing or being towed in certain configurations, vessels not under command, and vessels restricted in their ability to maneuver.
Vessels at Anchor
Rapid ringing of a bell for about 5 seconds, every minute (forward part of the vessel)
Vessels over 100 meters also sound a gong in the after part of the vessel
Vessels at anchor in a fog announce their position so other vessels can avoid them. Vessels under 20 meters (65 feet) are not required to sound anchor signals if they are in a special anchorage area.
Vessels Aground
Three strokes of bell, rapid ringing of bell for 5 seconds, then three strokes — every minute
The three strokes before and after the rapid ringing distinguish aground from at anchor. Remember: anchor signal is just the rapid ringing; aground is ring-ring-ring / rapid / ring-ring-ring.
Short vs. Prolonged Blasts: Definitions Matter
The exam uses these terms precisely:
Short blast: About 1 second duration
Prolonged blast: 4 to 6 seconds duration
Exam questions will describe a signal and ask you to identify it, or give you a situation and ask what signal is required. Knowing the exact definition of short vs. prolonged keeps you from confusing signals that look similar in text form.
The Exam Pattern: What to Watch For
The "underway but stopped" trap. A vessel can be underway (not anchored, moored, or aground) but not making way. Most students default to "one prolonged blast" for any underway vessel — but a power vessel at zero speed through the water sounds two prolonged blasts. The question will describe a vessel that has stopped its engines while waiting — it's underway but not making way.
International vs. Inland confusion. One short blast means different things on international vs. inland waters. Questions about maneuvering signals will specify the waters. Read the question carefully for "inland waters," "river," or "international rules."
Sailing vessel in restricted visibility. A sailing vessel sounds one prolonged + two short, same as a vessel fishing. Students who only memorize "the sailing signal" often miss that it's the same as several other vessel types. The signal identifies a category, not just sailing vessels specifically.
A Study Method That Works
Don't try to memorize these as a list. Instead, understand the logic:
Rule 34 = in sight, maneuvering signals (what you're doing)
Rule 35 = fog, status signals (what type of vessel, what state)
Power making way = one prolonged (moving, all clear)
Power stopped but underway = two prolonged (present but not moving)
Special vessels = one prolonged + two short (I'm constrained, give me room)
Anchored = bell ringing (I'm here, I'm not moving, don't hit me)
Aground = bracketed bell (three strokes, ring, three strokes)
Once the logic makes sense, the signals are much easier to hold in memory under exam pressure.
The COLREGS practice module includes a dedicated set of sound signal questions — drill them separately from the visual signal questions until you're consistently nailing both. If you're not yet using adaptive practice, start free here — sound signals will show up early and often.
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