Rule 35 fog signals: signaling in restricted visibility or when at a standstill to keep mariners safe.

Outline

• Opening: Why Rule 35 matters—fog signals as a lifeline when visibility vanishes

• What actually triggers a fog signal? The key condition: restricted visibility or when at a standstill

• What fog signals do for mariners: signaling presence, aiding orientation, reducing risk

• Common myths: high traffic, storms, or vessel size aren’t the trigger themselves

• How signaling looks in real life: simple patterns, intervals, and moments you’ll notice

• Practical tips: what to do when you hear signals, and what your signals should communicate

• A little context: tech helps, but fog signals remain essential

• Quick takeaway: keep calm, signal clearly, stay seen and heard

Fog signals: a lifeline when the sea forgets to show you the way

Let me ask you something: have you ever stood at the edge of a harbor at dusk, kidneys of fog rolling in, and realized how silence suddenly feels loud? In those moments, fog signals aren’t just noise—they’re the sea’s way of saying, “I’m here, and so are you.” That’s the heart of Rule 35 in the COLREGs: when visibility is restricted, fog signals become a shared language among vessels. They’re not about drama or bravado; they’re about safety, predictability, and helping every mariner make informed decisions when the world narrows to fog and distance.

What actually triggers a fog signal? The simple, honest answer is this: restricted visibility or when a vessel is at standstill. That’s the condition Rule 35 calls out. It’s not merely about whether the air is misty or whether the sea looks gray and moody. It’s about what you can and cannot see. If visibility is reduced so you can’t clearly identify other vessels’ positions and movements, you sound the fog signal. If a vessel is at anchor or not moving, that still falls under the same rule. The point is clarity in a moment when sight alone doesn’t do the job.

Contrast that with some common assumptions. People often think fog signals kick in just because there’s heavy traffic, or because weather is stormy, or because a ship is large. Those factors can complicate navigation, sure, but they don’t by themselves mandate fog signals under Rule 35. The rule centers on visibility—the sense of sight—more than the day’s pace or the weather’s mood. It’s about making your presence known when what you see isn’t enough.

What fog signals do for mariners

If you’ve ever watched a fogbound harbor at first light, you’ll notice a rhythm. Ships begin to sound signals at intervals. The idea isn’t to scare or to prove who’s louder; it’s to paint a sonore map of the surrounding lanes, showing where you are, what you’re doing, and where you’re headed. When visibility is restricted, a fog signal communicates several crucial things:

• Your presence: other vessels can sense there’s something ahead, even if they can’t discern it with their eyes.

• Your heading and speed: the tone and cadence help nearby mariners infer how you’re moving.

• Your intentions: whether you’re turning, stopping, or continuing on a path helps others adjust their own course.

• A shared safety net: it creates a predictable flow of information in a moment when visual cues vanish.

Think of fog signals like a maritime weather report you can hear rather than read. The sound becomes a cue, a way to reduce uncertainty in a space where uncertainty is easy to misinterpret. And yes, it’s a bit old-school in a world full of bright screens and radar indicators, but that’s part of the charm—and the reliability—of this tradition.

Common myths—and why they miss the mark

Here are a couple of ideas that sometimes creep into conversations about fog signals, and why they don’t quite fit Rule 35’s intent:

• “If there’s a lot of traffic, you must sound the signal.” Not exactly. Traffic density amplifies risk, sure, but the trigger is the lack of visibility, not sheer numbers. You could be in a quiet, foggy channel where signaling is essential, or you could be in a crowded area with clear visibility where signals aren’t required by Rule 35.

• “Stormy weather automatically means you’ll sound a fog signal.” Weather can affect visibility, but stormy conditions don’t automatically mandate fog signals unless visibility is restricted. Thunder and wind are dramatic; restricted visibility is what makes fog signals necessary.

• “Size equals responsibility.” A big ship isn’t exempt from Rule 35, and a tiny boat isn’t given a pass. The rule looks at what you can see, not how big you are. Still, the bigger vessels often have more robust signaling capability and crew on deck who are trained to maintain audible cues.

The mechanics—how signaling works in practice

You don’t need to memorize a long litany of patterns to understand the essence. In practice, when a vessel finds itself in restricted visibility or at a standstill, it uses sound to announce its presence. The signals are designed to be recognizable and unambiguous, so other mariners can quickly infer direction, speed, and intention. The cadence is steady, the intervals are predictable, and the sounds cut through the fog like a lighthouse’s pulse.

If you’re near other vessels and you hear a fog signal, you know someone is there, even if you can’t pick them out visually. Your next moves—reducing speed, altering course, or increasing watchfulness—become more informed decisions. And if you’re the one signaling, you’ve given others the mental model they need to stay safe.

Real-world touchpoints: radar, AIS, radios, and fog signals

Modern boats aren’t just horn-honking machines. They’re integrated systems: radar to detect echoes, AIS to identify nearby ships, VHF radios for quick communication, and automatic warning features. Fog signals fit into this ecosystem as a timeless backup and a fail-safe that doesn’t rely on electronics alone. They’re the human-audible reminder of shared space on the water.

That said, you’ll notice that signaling habits vary a bit by region, vessel type, and local practice. Larger commercial ships may have more formalized procedures, while small recreational boats keep things simple: sound when you need to, listen when others do, and keep watch. It’s a dance, really—one part tradition, one part modern safety discipline.

A practical mindset for captains and crew

If you’re onboard and you hear a fog signal, what should you do? Focus, first, on keeping a safe distance. Slow down, use your engines judiciously, and keep a sharp lookout. If you’re the vessel signaling, speak your presence in a clear, steady cadence and then maintain appropriate speed and course until you’re confident you’ve established mutual understanding with nearby traffic.

A quick, friendly checklist you can keep in mind:

• Check visibility and weather conditions. If they reduce your visibility to a point where you can’t safely navigate by sight, signal.

• Listen carefully to other fog signals and note their timing and cadence.

• Use radar and AIS to supplement the audible cue, but don’t rely solely on electronics.

• If you lose visual contact, reduce speed and proceed with caution. Your aim is “mutual awareness,” not speed.

• Communicate when appropriate—VHF can clarify intentions, especially in busy lanes or near harbor entrances.

A touch of storytelling: why these signals endure

I recall a harbor walk where the fog crept in like a soft curtain over the piers. The old-timer on the quay told me a story about a fog that swallowed the harbor in minutes, where a single fog signal saved a collision because one vessel listened, one listened back, and both adjusted. Stories like that aren’t just nostalgia; they’re reminders that even in the age of glass cockpit displays, the fog signal remains a straightforward, reliable tool. It’s a reminder that safety, at its core, comes from people paying attention and communicating clearly.

Useful analogies to keep in mind

• Fog signals are like car horns in a tunnel. If you can’t see the car in front of you, you rely on the horn to signal presence and intent.

• Think of restricted visibility as a whiteout in the sea. The fog signal is your compass for the human element of navigation—an audible cue that steadies the ship of state when sight fails.

• It’s not about being loud; it’s about being understood. The goal is shared situational awareness, not a show of force.

Final takeaway: clarity over cleverness

Rule 35 isn’t trying to trap anyone with complex directives. It’s a practical rule that keeps mariners safe when visibility is the enemy. Restricted visibility or being at a standstill is your cue to sound the fog signal. It’s the simplest, most direct way to tell others, “I’m here, I’m moving or I’m not, and I’m watching out for you.”

If you’re ever in a fog, remember this: sounds carry farther than you see, and a fog signal is a lifeline. Respect it. Use it. And when you hear one, give the crew on watch your full attention. The water is beautiful and boundless, but it’s also loud and exact. And in those moments, precise communication matters more than ever.

Glossary for quick recall

• Fog signal: an audible signal used to communicate presence and intent in restricted visibility.

• Rule 35: the section of COLREGs that governs fog signals and related actions when visibility is limited.

• Restricted visibility: conditions where vessels cannot clearly see other vessels due to fog, rain, or other atmospheric effects.

• Standstill: when a vessel is not moving, still requiring signaling under Rule 35 to ensure other boats know it’s there.

If you’re curious about more maritime rules, remember the sea has a way of teaching through experience. You learn by doing, by watching others, and by staying curious about how signals—whether lights, radio calls, or sound—keep the vast ocean navigable for everyone aboard.