The signal of three bell claps followed by a whistle indicates an aground vessel under COLREGs

What does a grounded boat sound like? If you’re listening closely out on the water, it’s not just noise—it’s guidance. In the world of COLREGs, sound signals are the language sailors use to share status, intention, and warning. And one signal, in particular, is made to stand out: three bell claps followed by a whistle. That’s the telltale cue for a vessel that’s aground or otherwise unable to maneuver.

Let me explain how that signal fits into the bigger picture of keeping the water safe for everyone.

The purpose of sound signals in COLREGs

Imagine you’re cruising through a busy channel or a windy harbor. Boats, ferries, tugs, and fishing vessels are all moving at different speeds and directions. Without a common language, a near-m collision could happen in a heartbeat. That’s where sound signals come in. They’re simple, portable, and effective even when visibility is poor.

The rules give mariners a vocabulary of signals to convey a vessel’s status or a necessary action. Some signals announce a maneuver, others request or acknowledge coordination with nearby traffic. They’re designed to be recognizable from a distance, short enough to be heard over engines and wind, and specific enough to reduce guesswork.

Here’s the thing about the aground signal

When a vessel finds itself aground or unable to move, the COLREGs prescribe a precise audible indication: three bell claps, followed by a whistle. The bells are the marker—three quick taps signals “I’m grounded.” The whistle adds an extra cautionary layer, a warning to others that this vessel cannot safely maneuver to avoid a collision.

You might wonder: why bells and a whistle? Bells are long-standing maritime signaling tools with good audibility in open water, while a whistle can be heard over engine noise and in various weather conditions. Put together, they create a clear, unmistakable message: “Here I am, I’m stuck, and I can’t get out of your way right now.”

What this signal communicates to other vessels

• Status: The vessel is aground or immobilized. It can’t take timely action to avoid danger.

• Intent: The vessel isn’t able to maneuver to clear a potential collision course.

• Caution: Other mariners should reduce speed, increase alertness, and give the grounded vessel a wide berth.

Recognizing the signal in the real world

You’ll hear this combination most often in shallow bays, near sandbars, or around shoreline channels where grounding is more likely—especially after a storm, during changing tides, or when navigation marks are uncertain. On a clear day with good visibility, you might spot a grounded vessel visually, but a sound signal ensures there’s no ambiguity. Even in the age of AIS and radios, those bell taps and a whistle cut through the noise and tell nearby traffic exactly what’s happening.

If you’re at the helm or on deck nearby, what should you do?

• Stay calm and assess: Is the vessel truly aground, or is there a risk of becoming aground? Sometimes a vessel might be near a shoal or a shallow patch but has just found stable ground. Either way, treat it as a safety situation.

• Give space: Slow down and steer clear. Move to a safe distance to avoid sideswipes or drifting into the grounded vessel as currents and wind shift.

• Communicate clearly: If you’re within VHF radio range, establish contact with the grounded vessel or nearby traffic to coordinate. A calm, concise radio message can prevent confusion.

• Monitor the situation: Keep an eye on tides, weather changes, and any movement of the grounded vessel. If the situation shifts (for example, if the vessel begins to slip off the ground), be ready to adjust course again.

• Be prepared for action: Sometimes relief tugs or assistance may be needed. If you’re responsible for safe navigation in the area, stay informed about rescue or salvage operations and follow instructions from authorities.

A few practical notes for mariners on the water

• Sound signals aren’t a substitute for visual contact or radio communication. They’re complementary tools that reduce ambiguity.

• Noise discipline matters. In busy waterways, the same signal repeated at intervals (as required by the rule) helps ensure every nearby vessel recognizes the situation, even if you’re not looking right at the grounded boat.

• Nighttime signals can be harder to pick up. If you’re piloting in low light, rely on a combination of sounds, lights, and, where appropriate, radio chatter to stay aware of where all boats are and what they’re doing.

• Different waterways, different expectations. Rules can be tailored to local conditions, so it’s wise to know the common signals used in your region or passage area.

A quick mental checklist, so you don’t miss a beat

• Do I know the sound signals well enough to recognize them under stress or in rough weather?

• If I hear three bell taps followed by a whistle, am I maintaining a safe distance and ready to adjust speed?

• Am I using radio and, when appropriate, lights to confirm what’s happening with the grounded vessel and nearby traffic?

• Do I have a plan for what to do if the situation worsens or if the vessel becomes unstuck and starts moving again?

A bit of context that makes this signal feel less abstract

Maritime signaling isn’t about drama; it’s about reliability. Think of it as the nautical equivalent of a road sign you can hear in a noisy street. You don’t need perfect vision to understand “grounded ahead” once you hear those three bell claps and a whistle. And because water can throw you a curveball—wind, current, fog—the sound signal gives you a consistent cue you can count on when other cues are muddled.

If you like analogies, picture a group of hikers crossing a windy pass. If one person stops in a choke point, they might shout a quick cue to the others to slow down and step aside. On the water, the bell taps and whistle are that whistle-and-tapered-shout, signaling a safe pause and alerting others to the obstacle ahead.

Where this fits into the broader rules of the road

COLREGs aren’t just a long list of do’s and don’ts. They’re a living toolkit for safe navigation. The aground signal sits alongside other critical signals—like those for vessels not under command, vessels constrained by draft, or vessels in distress. Each signal has its moment, its message, and its audience. The common thread is clear communication: you want nearby mariners to know your status quickly and act accordingly.

So, what’s the takeaway?

That three bells and a whistle aren’t just a quirky maritime habit. They’re a direct, practical, and urgent message: “I’m stuck, I can’t move, and I need room to protect everyone.” For anyone who spends time on the water—whether in a busy harbor, a quiet inlet, or a coastal reach—knowing this signal isn’t just academic. It’s a safety tool you hope never to need, but you’ll be grateful for if you ever do.

A friendly nudge toward familiarity

If you’re curious about sound signals in other situations, it’s worth taking a moment to listen to the full spectrum of COLREGs audio cues. From single short blasts to prolonged notes and combinations, each pattern has its own role. The more you recognize them, the more fluid your navigation becomes, even when visibility is less than ideal.

In the end, the water doesn’t care for our plans or our schedules. It cares for patience, vigilance, and respect. The grounded vessel signal—three bell claps followed by a whistle—embodies that ethos: a small, precise cue that keeps traffic orderly and people safe. And that matters more than any shortcut or quick maneuver.

If you’re ever out there and you catch that trio of bells and a whistle, you’ll know what it means. You’ll slow, you’ll listen, you’ll look, and you’ll act. Not because you have to, but because those signals are reminders that, on the water, clear communication saves lives—and that’s a principle worth keeping close, no matter what you sail.