Sound signals must be used at least once every two minutes in restricted visibility.

Fog rolls in, and suddenly the waterway goes quiet in a way that feels almost deliberate. You can’t rely on sight alone—things disappear behind mist, or loom in a shadowy silhouette. In those moments, sound signals become more than a courtesy; they’re a lifeline. This is where COLREGs Rules of the Road step in and remind us that communication isn’t optional. It’s a duty, especially when visibility is restricted.

Two-minute rhythm: what the rule actually says

Here’s the thing about restricted visibility on the water: you’re expected to keep others informed of your presence and intentions. The rule most people remember for this is straightforward—sound signals need to be used at least once every two minutes. That cadence isn’t random. It’s designed to create a steady, audible “neighborhood watch” for nearby vessels, even when you can’t rely on your eyes to tell the full story.

Why two minutes, not one minute or five?

You might wonder why not a tighter or looser schedule. The answer is practical. In fog, rain, or heavy spray, sight cues vanish and sound becomes the primary communicator. If you cue your signals too rarely, other boats might drift into your blind spot without realizing you’re there. If you signal every minute, you might overwhelm listeners and cause fatigue or confusion—sound has to stand out, not blend in. The two-minute rule gives a reliable rhythm that most mariners can anticipate, which reduces the chance of misunderstandings that lead to close calls.

What counts as restricted visibility?

Restricted visibility isn’t only thick fog, though that’s the classic example. It also includes heavy rain, snow, sandstorms, or any condition that makes it hard to see another vessel at a distance where you could prevent a collision with normal steering and speed. In these conditions, you should supplement your visual lookout with sound signals and, when available, use lights to enhance visibility at night. The goal is to establish a clear, ongoing line of communication with other mariners so your presence and actions aren’t left to chance.

What sounds and signals should you use?

Sound signals come in several forms, with whistles and horns being the most common aboard commercial and recreational vessels. Bells and other signaling devices have their places too, especially on smaller craft that might not carry the same whistle equipment. The precise pattern of blasts isn’t the focus of the rule that governs the two-minute interval; rather, it’s the consistent use of a signal to indicate “I’m here, and I’m moving in this way” or “I’m slowing/altering course.”

In practical terms, most crews use a cadence that’s recognizable and repeatable—think of a prolonged blast followed by shorter blasts, repeated as needed. The exact cadence can vary by vessel type and local practice, but the important part is consistency: every two minutes, you emit a signal that’s audible to nearby traffic. If you do see another vessel, you adjust your signals to convey your status and intentions, always keeping a careful watch and maintaining a safe speed.

A mental model you can carry on deck

Let me explain with a simple image. Picture your sound signal as a lighthouse horn in the fog—a beacon that tells others, “I’m here, and I’m not ignoring you.” Two minutes feels slow when you’re anxious about a potential crossing, but it’s fast enough to stay relevant without turning into white noise. The beauty of this approach is that it doesn’t demand fancy equipment or perfect conditions; it just asks you to keep your ears and your plan in tune with the rules.

What this means in everyday boating

• Stay alert to the weather window. If visibility deteriorates, switch on lights as required and start the two-minute signaling rhythm.

• Use your whistle or horn as your primary audible cue, but don’t neglect other devices you have onboard. Bells on a small workboat, or a backup horn on a larger vessel, can provide redundancy in noisy environments.

• Coordinate with other vessels. If you notice another craft in the vicinity, maintain your signals and adjust course or speed only after confirming their position as best you can by sight and radar if available.

• Keep a steady watch. The best signaling won’t help if you’re not actively watching and listening. A vigilant lookout complements the two-minute cadence and reduces the odds of a near-miss.

Real-life tangents that still loop back to the main point

You might ask, “What about day VFR travel and the enjoyment of peaceful waterways?” Even then, restricted visibility can sneak up—mist, river fog, or a sudden thunderstorm can rob you of visual cues. In those moments, your sound signals become a shield, not a prop. And yes, it’s a bit more wearing to maintain that routine when you’re tired or docked at a busy harbor, but consistency matters for safety.

If you ever wonder how professionals balance strict rules with the unpredictable nature of the sea, consider this: rules aren’t there to hinder freedom; they’re there to preserve it. When everyone follows the same rhythm, ships move more predictably, and chances of collision go down. It’s a shared habit that pays off in calmer seas and clearer afternoons.

A few practical tips you can put to use

• Test your equipment regularly. Make sure your whistle or horn works, that your battery-powered signaling devices are charged, and that any adjustable tones are audible at the distances you typically encounter in your routes.

• Practice the cadence. On a calm day, run through a mental and audible checklist: I’m signaling now, I’ll signal again in two minutes, and here’s what I’ll do if I detect another vessel.

• Combine with light signals. A steady white light or a rotating beacon can reinforce your presence when you’re using sound signals. In fog, light and sound together create a stronger, complementary signal.

• Don’t rely on sound alone. Keep eyes peeled and use radar, AIS, or VHF where available. Sound is essential in restricted visibility, but it’s most effective when paired with other tools and good seamanship.

• Share the workload. If you’re on watch with others, assign roles so one person manages the lookout while another handles the signaling cadence. It’s easy to drift off rhythm if you’re multitasking.

Common misconceptions worth clearing up

• “Only signal when I’m sure someone can see me.” Not true. The rule exists precisely because visibility is compromised. Signal regularly to inform others of your presence, even if you think you’ve already been seen.

• “I’ll just slow down and listen.” Slowing helps, but it doesn’t replace the need to signal. In restricted visibility, your speed and your signals work together to reduce risk.

• “If I’m close to shore or crowded water, signals aren’t necessary.” They are. The same rules apply, and the fog can smear the distance to the point where you can no longer rely on sight alone.

A practical takeaway for captains and crews

The rule is fundamentally about reliability. In environments where perception is limited, predictability is your best ally. Embrace the two-minute signaling rhythm as part of your everyday operating discipline. Treat it like a dependable routine you trust even when conditions look ordinary. The more consistently you apply it, the more natural it becomes to your crew, and the safer the voyage will be for everyone on board.

Closing thought: safety is a conversation, not a solo act

Sound signals in restricted visibility aren’t a gimmick; they’re a conversation with other mariners, a way of saying, “I’m here, and I’m moving forward with care.” When you honor that conversation, you reduce the likelihood of misinterpretation and the chance of a dangerous situation escalating. So next time the fog thickens, listen for the rhythm around you and respond with calm, deliberate signaling. The water may be quiet, but your vessel’s voice should be clear.

In the end, staying visible and audible is more than a rule—it's a habit that protects life at sea. And like any good habit, it’s built from small, consistent actions that you can carry from one voyage to the next. If you keep that cadence in mind, you’ll navigate not just the fog, but the whole spectrum of sailing with a little more confidence and a lot more peace of mind.