Rule 39 and restricted visibility: navigating safely under COLREGs

Outline (quick skeleton)

• Opening hook: fog, engines, and the rhythm of sound

• What Rule 39 is really about: signals in restricted visibility

• Why it matters: safety, predictability, and smoother teamwork at sea

• What vessels should do in restricted visibility

• Use sound signals to indicate presence and intentions

• Slow down and be prepared to adjust course

• Keep a careful lookout and use all available tools

• What Rule 39 is not about (clarifying common confusions)

• Not daytime light signals

• Not aircraft signals

• Not distress signals

• Practical tips and real-life flavor

• How to interpret signals on a busy waterway

• A quick mental checklist for fog or heavy rain

• Tools of the trade: radar, AIS, radios, and good seamanship

• Common mistakes and how to avoid them

• Takeaways: the calm sound of safety in murky conditions

• Closing thought: practice, patience, and paying attention to the sea

Rule 39: The sound of safety when the sea goes quiet

Let me set the scene: you’re sailing along just off a busy coast, and a damp, gray veil slips across the water. The horizon, once a crisp line, dissolves into mist. You can’t rely on sight alone. In that moment, Rule 39 isn’t a fancy rule to memorize; it’s a practical habit that keeps people on board safe. In the COLREGs, Rule 39 is all about how vessels communicate in restricted visibility. It isn’t about aircraft, it isn’t about daytime light signals, and it isn’t about distress calls. It’s about the quiet, steady language of sound signals that tells other ships where you are and what you intend to do.

Why restricted visibility matters is simple and human: when you can’t see well, staying predictable is priceless. Other boats can be near without you realizing it, and misinterpretation is a real risk. The whole point of Rule 39 is to reduce that risk by making your presence and intentions known through sound. It’s like someone tapping you on the shoulder when you can’t quite locate them by sight—a reliable cue in murky conditions.

What you actually do in restricted visibility

• Sound signals to announce presence and intentions

In fog or heavy rain, you switch on the nautical blinker of communication: sound. The vessels listen for signals that tell them you’re there and what you’re doing. This isn’t about loud bravado; it’s about a steady, predictable cadence that others can recognize and react to. You might hear or emit signals that indicate your status, speed, and maneuvers. The key is consistency and clarity. If you’re moving, you signal; if you’re stopping, you signal; if you’re overtaking or crossing, you signal your course change.

• Slow down and navigate cautiously

Visibility aside, speed becomes a moving safety feature. Slowing down gives you more time to react to what you can’t see yet. It also gives others a chance to pick you up on their radar, AIS, or, yes, by sound. The combination of reduced speed and clear signaling often prevents near-misses and gives everyone a margin for error.

• Be ready to take evasive action

In fog, the best plan is to assume you aren’t the only vessel out there. You stay ready to alter your course slightly to avoid a risk of collision. That posture—predictable, patient, prepared—often makes the difference between a tense moment and a safe passage.

• Maintain a good look-out with all the senses

Eyes aren’t the only tools here. A vigilant lookout, enabled by instruments, keeps you in the loop. Listen for other signals, monitor VHF, check radar returns if you have them, and pay attention to AIS. The more channels you keep open, the better your situational awareness becomes.

What Rule 39 is not about (to clear up the confusion)

• It isn’t about daytime light signals

Light patterns and shapes are governed by other rules. Rule 39 focuses on sound signals and the general procedures for operating in restricted visibility. Daytime signaling tends to belong to different articles of the COLREGs.

• It isn’t about aircraft signals

Aircraft signals are outside the maritime rules that govern ships at sea. The world of COLREGs is a waterborne conversation; air traffic has its own set of rules, charts, and standards.

• It isn’t a scattered list of distress protocols

Distress signaling has its own dedicated rules and methods. In restricted visibility, you’re working to prevent danger by sharing your presence and intent, not shouting for help. Distress signals come into play when safety is at risk and life-saving actions are necessary.

A practical lens: turning knowledge into steady action

Let me explain with a quick mental model. Imagine you’re driving through a thick fog with your car’s wipers buzzing and the headlamps cutting a pale circle in front of you. You don’t expect to see everything, but you do expect to be seen and to know what the other drivers intend. On the water, Rule 39 operates the same way: you create a simple, common language that others can hear and trust. In practice, that means:

• Deploying standard fog signals

If you’re underway in restricted visibility, you’ll use sound signals to convey your presence. A regular, planned cadence communicates that you’re not a mystery in the mist. It’s not dramatic; it’s dependable.

• Listening as a skill

The sea is full of little cues. A distant horn, a radar blip, a radio call on Channel 16—these are your cues. You listen, interpret, and respond. It’s a bit like driving with your ears first.

• Keeping the ship “in tune” with the weather

Fog and rain can mask speed and distance. Reducing speed, allowing extra space, and staying mindful of the wind and current help keep you from overreacting to a false sense of proximity.

• The social contract of the sea

Rules aren’t just regulations; they’re the social contract that makes navigation safe. Rule 39 is a reminder that you’re part of a wider traffic system, and your signals are part of a shared language that keeps everyone moving safely.

A few handy, real-life touches

• Fog is not a settings screen; it’s a condition

Fog isn’t just a weather feature; it changes how every boat behaves. You’ll hear more sound signals than you might expect, and you’ll notice slower movement on the water. That’s not a weakness; it’s wisdom in practice.

• Tools help, but they don’t replace judgment

Radar, AIS, GPS, and radios are your teammates, but they don’t replace a steady lookout. Combine technology with good seamanship and you have a resilient safety net.

• Communication is a two-way street

It’s not enough to emit signals; you also have to listen and interpret others’ signals. If you hear a sound signal that seems to point toward your vessel, you must assess the risk, adjust, and confirm your own intentions.

A quick checklist to keep in mind

• In restricted visibility, do you have the vessel’s sound-signaling plan in mind?

• Are you reducing speed appropriately for the conditions?

• Is your lookout sharp, and are you cross-checking radar/AIS?

• Are you ready to alter course to avoid a collision, even if it means a small adjustment?

• Do you have a clear plan for communications with nearby vessels if needed?

This is where the craft of seamanship meets the science of safety. It’s a dance—you move with the fog, other vessels move with you, and everybody keeps a little extra distance just in case.

Making sense of the fog with the right mindset

Let me offer a small analogy. Think of Rule 39 as the fog’s neighbors in a quiet street: you nod to each other, you signal your intentions with a wave or a shout, and you slow down until the street is clear. The sea is full of similar moments. When you can’t see far ahead, you lean on sound, slow your pace, and keep a steady, predictable rhythm that others can follow. That calm, methodical approach reduces tension and lowers the chances of a collision.

A note on practice signals and everyday wisdom

One common snag is assuming that signaling alone solves the whole problem. Signals are essential, but they work best in concert with situational awareness and prudent speed. If you’re in doubt about another vessel’s intentions, communicate clearly, give space, and be prepared to adjust again. You’ll often find that a well-communicated plan is as effective as a bold move.

Wrapping it up: Rule 39 in one sentence

In restricted visibility, reliability matters most. Use sound signals to announce your presence and intentions, slow down, keep a vigilant lookout, and stay ready to maneuver safely. When the fog closes in, good communication becomes your compass.

A closing thought

The sea has its moods, and fog is a patient teacher. Rule 39 isn’t flashy, but it’s profoundly practical. It reminds sailors to favor clarity over cleverness and to respect the rhythm of the water. If you remember that, you’ll navigate those misty hours with a steadier hand and a sharper sense of safety.

If you’re curious, many mariners also find value in reviewing real-world scenarios—foggy mornings near busy harbors, a coastal squall driving a line of vessels into a single channel, or the way a small boat signals its approach to a larger ship. The essence remains the same: in restricted visibility, sound, speed, look-out, and a cooperative mindset are your best tools. And in the end, that shared language is what keeps every voyage safer, smoother, and a little more human.