When is a vessel in restricted visibility? A practical look at COLREGs rules and safe navigation.

Let the Mast Point: Understanding Restricted Visibility in COLREGs

Here’s a scene that could be straight from a maritime novel: the sun goes down, a mist rolls in, and suddenly the shoreline blurs into a gray outline. The radar becomes a trusted friend, and the only way to stay on course is to trust your instruments, your crew, and the rules that keep people safer on the water. One phrase you’ll hear a lot in studying the COLREGs is “restricted visibility.” It sounds clinical, but it’s really about a very human truth: when you can’t see the people around you, you have to change how you move.

Quiz moment to start

Let me ask you a quick check-in: When are vessels considered to be in “restricted visibility”?

• A) When they are operating at high speeds

• B) When they cannot see each other by eye

• C) When navigating in shallow waters

• D) When there are many other vessels around

If you picked B, you’re right. Restricted visibility isn’t about speed, or depth, or crowding. It’s about sight—the moment you can’t reliably see other vessels with your eyes. Fog, heavy rain, night darkness, or spray that hides the horizon all count. In those moments, the COLREGs shift from “visual awareness” to a broader, instrument-assisted, safeguard-focused mindset. That’s why the rules emphasize safe speed, the use of sound signals, and heightened vigilance. Now, let’s unpack what that actually means on deck.

What restricted visibility really means, in plain terms

Restricted visibility is more than a weather forecast. It’s a condition in which the human eye can’t reliably spot a vessel in time to avoid a collision. Think of it like driving on a coastal road with a thick fog. You slow down. You rely on the windshield wipers, the headlights, perhaps the GPS and the car’s sonar if you’re lucky. On a vessel, you have similar tools plus a few extra: radar, AIS, VHF communications, and careful watchkeeping.

In the COLREGs, restricted visibility triggers a different set of safe habits. It isn’t about racing to get somewhere fast; it’s about maintaining a margin of safety equal to the uncertainty in what you can’t see. The idea is simple, even if the details can feel thorny: visibility is compromised, so you compensate with cautious speed, precise navigation, and clear communication.

What you should do when visibility is restricted

Inside the limits of restricted visibility, a few core principles guide every action:

• Safe speed, adapted to conditions: This isn’t a rough guess. It means choosing a speed you can safely maneuver at, given wind, current, traffic density, and your vessel’s maneuvering characteristics. If you’re unsure, you slow down further. The goal isn’t to arrive sooner; it’s to arrive alive and well.

• Use of sound signals: In the fog, sound becomes the extra sense. Vessels should use appropriate sound signals to communicate intentions and position. The exact signals are part of the COLREGs, but the heart of it is a steady, predictable pattern that other vessels can hear and interpret even when they can’t see you.

• Extra lookout and use of all available navigation aids: Lookouts aren’t optional luxuries in restricted visibility—they’re essential. In addition, you’ll lean on radar, AIS, GPS, depth sounders, and, if you have it, electronic chart systems. Cross-check everything, because seeing is unreliable.

• Early and deliberate actions to avoid collisions: If a potential risk is spotted, you act early and clearly. The goal is to reduce uncertainty and give others room to react. It’s not about heroics; it’s about predictable, disciplined behavior.

• Communications: Keep a steady watch on the radio, use VHF to coordinate with nearby traffic if needed, and report any hazards when appropriate. Clear communication reduces the chances of misunderstandings in the murk.

A few practical notes for everyday sailors

Restricted visibility isn’t reserved for ocean-going ships; it can sprout in a suburban inlet or a busy harbor at dusk. Here are some practical habits that help:

• Plan your route with the weather and visibility in mind: If the forecast calls for thick fog overnight, study the traffic pattern in your area. Is there a busy shipping lane nearby? Are there channels with restricted visibility advisories? Plan alternates if reasonable.

• Slow and steady wins in the fog: You don’t have to halve your speed every time you glimpse fog, but you should drop to a level where you can stop within the distance you can clearly see and the distance your radar can resolve. It’s about a comfortable safety margin.

• Master your instruments, but don’t forget your human senses: Instruments give you a map of the world, but you still need lookouts and a crew you trust. The fog doesn’t care how precise your numbers are; it cares about what you do with them.

• Practice good radar hygiene: Keep your radar range appropriate for the segment you’re in and learn to plot relative motion. If you’re near channels or narrow passages, radar can reveal vessels that your eyes miss.

• Use AIS thoughtfully: If other vessels are transmitting AIS data, use it to your situational awareness. Don’t rely on it exclusively—cross-check with radar and visual cues.

Common misunderstandings that can trip you up

A lot of confusion around restricted visibility comes from assuming it’s only about fog or night. Here are a couple of clarifications that help when the seas look gray:

• It’s not about who’s big or loud: Small boats, sailboats, ferries, and cargo ships all apply. Restricted visibility is a condition, not a vessel class. Everyone on the water has a responsibility to act predictably.

• The “stand-on” idea has teeth in the mist: In unrestricted visibility, you sometimes hear the phrases “stand-on vessel” and “give-way vessel.” In restricted visibility, the emphasis is on safe speed and clear maneuvering for everyone. It’s not a license to push through; it’s a reminder to be extra cautious and communicate clearly.

• Visual priority shifts to a layered safety approach: When you can’t see, you can still be seen through radar, AIS, and lights, but only if you maintain proper lookout and keep a steady, predictable course—no sudden maneuvers that surprise others who might only detect you by sound or radar.

A quick sense-check with a real-world flavor

Imagine you’re piloting a small fishing boat near a busy coast while a dense fog bank closes in. You hear a distant fog horn from a large cargo ship, and your radar starts painting ghost ships as you sweep the compass rose. You still need to look out the window, but your confidence rests on your disciplined speed, your use of sound, and your ability to interpret what the radar shows you in relation to your own path. The fog isn’t an obstacle you bully with raw speed; it’s a condition you respect with a clear plan, precise instruments, and steady hands on the wheel.

Why this matters beyond a single rule

Restricted visibility is a reminder that a successful voyage isn’t about who can drive fastest through the fog; it’s about who can read the signs the weather gives you and respond with discipline. The COLREGs are a living map, built from years of real-world scenarios where a split-second difference in judgment can make the difference between a safe return and a dangerous outcome. When visibility drops, the rules become a safety net that keeps everyone moving with intention rather than impulse.

A closing thought to carry on deck

If you remember one thing about restricted visibility, let it be this: your eyes aren’t the only guide. Instruments count, but so do habits—how you communicate, how you slow down, and how you stay ready to react. In fog, every change in speed, every turn of the wheel, and every sound signal tells a small part of the bigger story of safe navigation.

Now, back to that initial question one more time, in case it sticks: restricted visibility means you can’t see other vessels by eye. It’s your cue to lean on signals, instruments, and careful planning to keep everyone safe. The water becomes a different kind of classroom in those moments, and the rules aren’t a checklist to memorize so much as a practiced way of thinking—steady, prudent, and clear.

A few bite-sized tips to keep in mind

• Slow down early, then verify with radar and AIS.

• Keep a continuous listening watch on the radio; share information when it helps reduce risk.

• Use sound signals in a steady, predictable pattern to announce your presence and intentions.

• Stay well clear of potential hazards you can’t see until they’re almost on top of you.

• Revisit the basics: look-out, safe speed, and compliance with sound signaling rules—these aren’t old-school notions; they’re the core of staying safe when the mist thickens.

Whether you’re on a coastal sailboat or piloting a working vessel, restricted visibility is a real, practical challenge. But with calm judgment, the right tools, and a clear plan, you can meet it head-on. After all, grace on the water isn’t about luck—it’s about preparation meeting opportunity, time after time.