Rule 19 explains how vessels should conduct themselves in restricted visibility to prevent collisions.

Fog is not just weather; it’s a blanket that hides the world from your eyes. When you’re navigating a vessel, that blanket becomes a compass of its own, nudging you toward caution, discipline, and clear-headed action. Rule 19 of the COLREGs—the rules that govern maritime traffic—addresses exactly this moment: what a ship should do when visibility is restricted. If you want to stay safe out there, here’s the thing you need to internalize: Rule 19 isn’t a checklist for a moment; it’s a mindset for a condition.

What Rule 19 is really about

Rule 19 is all about conduct in restricted visibility. In plain language, it tells every vessel to slow down to a safe speed for the conditions, maintain a proper lookout, use all available means to detect other vessels (including radar and AIS), and take early, substantial action to avoid collisions. It also calls for sound signals appropriate to fog or restricted visibility and emphasizes heightened vigilance since other boats you can’t see may be there, just beyond the dim edge of your visibility.

Why this rule matters beyond the checklist

Think of Rule 19 as the seam in seamanship where theory meets reality. In clear conditions, you can rely on sight to judge risk, assume others will do the reasonable thing, and keep moving with some padding in your plan. In restricted visibility, sight can betray you. A radar screen becomes your friend, your ears become more important than your eyes, and “reasonable” actions must be measured, deliberate, and early. The rule isn’t about catching someone out; it’s about creating a culture of caution that reduces the chance of collision when you can’t be sure what’s around the next bend.

Let’s unpack what “restricted visibility” really means

Restricted visibility isn’t just fog on a sunny day. It includes heavy rain, spray, drizzle, haze, snow squalls, or even a busy harbor at dawn when lights blur together. In those moments, you’re sharing the water with boats you may not immediately detect. Your decisions must reflect that reality.

• Safe speed is not the same as maximum speed. Safe means adjusted to the conditions—wind, current, traffic density, radar performance, and the ability to stop within the distance you can see or detect with other means.

• Lookouts aren’t a courtesy; they’re a necessity. Eyes on the water, ears for engine sounds, and the ability to interpret noises that might hint at a vessel’s position—these all matter more when you can’t rely on sight alone.

• The radar and AIS are not gadgets. They’re part of your ongoing weather report for the sea. If you’ve got the gear, you’re expected to use it to determine whether you’re on a collision course with a vessel that might be only a ghost on the horizon.

• Sound signals aren’t theatrical; they’re practical. Fog signals alert nearby vessels to your presence and movement when visibility hides you from them. The right signal at the right time communicates intent and reduces anxiety on the other end of the water.

Practical actions that embody Rule 19

Here’s how you translate Rule 19 into real-world behavior. Picture yourself on deck, hands steady, mind alert.

• Slow down, but don’t stop thinking

A reduced speed gives you more time to react if something appears or crosses your path. It also reduces the energy you might need to maneuver suddenly if you discover a risk of collision.

• Keep a meticulous lookout

In restricted visibility, the lookout isn’t just about what you can see with your eyes. It’s a multi-sensory habit: listen for engine noises, watch for lights that don’t belong to your own vessel, pay attention to the wake patterns, and stay aware of the hull’s soundscape.

• Use every available tool

If you have radar, use it to assess traffic and potential crossing situations. If you’re equipped with AIS, monitor it for other vessels, especially those that aren’t showing bright lights or are maneuvering oddly. Don’t rely on these tools alone, but let them augment your situational awareness.

• Maintain and communicate with a plan

Having a plan in restricted visibility isn’t something you think about once you’re there; it’s something you practice in calm conditions so it becomes second nature. Agree on a course of action with the crew: who will adjust speed, who will alter course slightly, who monitors the radar screen, and how you will confirm a safe distance from other vessels.

• Be prepared to maneuver early

Rule 19 encourages early action. If you detect a risk of collision, reduce speed further and start your maneuver as soon as practical. It’s easier to adjust gradually than to correct a late decision.

• Sound signals and right-of-way basics

Fog signals are a universal language in restricted visibility. They let other mariners know where you are and what you’re doing, even when your lights are less visible. Alongside signaling, remember that the COLREGs don’t grant a license to ignore basic safety: you still need to avoid hazardous situations with clear, predictable movements.

• Pause, reassess, repeat

Visibility can shift quickly. A gray wall can clear a bit, then thicken again. Constant reassessment is your ally. If the risk level changes, adjust your speed and course accordingly, and keep everyone on board informed.

Equipment and training you can rely on

If you’re cruising through fog or rough weather, you’re leaning on certain technologies and procedures to keep you on safe footing.

• Radar and ARPA

Modern radars with tracking capabilities offer a window into the unseen. If you’re practicing rule-based navigation, learn what a closing target looks like on radar, how to estimate range and bearing changes, and what constitutes a safe margin.

• AIS

Automatic Identification System helps you see other vessels’ movements, speeds, and headings. It’s especially valuable when power-driven craft are low on personal visibility.

• VHF radio

When a risk is detected, quick, precise coordination can prevent misinterpretations. A short, calm radio exchange can clarify intentions and reduce the chance of a collision.

• Sound signaling devices

A reliable fog horn or whistle isn’t decoration. It’s a critical line of communication when you can’t rely on sight. Make sure the signals are loud enough to be heard at the expected distances and in the prevailing wind and sea conditions.

• Bridge resource management

A strong lookout, a calm captain, and a crew that communicates well under pressure — these soft skills are part of Rule 19 too. It’s not just about the gear; it’s about how the team uses the gear together.

Real-world perspective: why this isn’t just theory

Rule 19 isn’t about showing off your knowledge of regulations. It’s about a shared discipline that keeps people safe when the sea turns gray. In the real world, you’ll hear stories of near-misses that were avoided because someone slowed down in time, used a radar check, and signaled their presence clearly. You’ll also hear about the moments when a vessel misread fog signals or assumed visibility would come back quickly, only to find a dangerous crossing ahead.

For students who care about more than just memorizing numbers, this rule is a reminder that good seamanship blends science, tools, and judgment. It’s the difference between a routine trip and a life-threatening incident.

Common pitfalls—and how to sidestep them

Even seasoned mariners slip here sometimes. A few pitfalls worth watching for:

• Overreliance on sight in the wrong conditions

You can’t rely on eyes alone in dense fog or heavy rain. Use the radar, listen for signals, and keep a careful lookout.

• Underestimating other vessels’ speeds

In limited visibility, it can be hard to judge how fast another vessel is moving. Give yourself extra space and assume a more conservative crossing.

• Delayed action

Hesitation can be costly. If you’re on a collision course in fog, act early and decisively.

• Poor crew communication

In a pinch, the crew can slip into uncertainty. Clear roles, simple phrases, and practiced handoffs keep everyone aligned.

A quick mental model for navigating foggy waters

Let me explain a simple way to think about Rule 19 in the moment:

• Look: keep a steady, multi-sensory lookout.

• Listen: use the fog signals and listen for engine noise or other vessel activities.

• Plan: decide on a safe speed and a predictable course change, if needed.

• Act: implement the plan early and smoothly.

• Confirm: verify that you’ve achieved a safe margin, and keep communicating with your crew.

That loop isn’t heavy; it’s practical enough to be second nature after a few sessions on deck or in a simulator. And when you’re out on the water, that “second nature” saves time, reduces risk, and helps you stay focused where it matters most.

A final thought about Rule 19

The sea doesn’t care about your schedule or your pride. In restricted visibility, it rewards humility, preparation, and teamwork. Rule 19 isn’t about punishing you for not seeing everything at once; it’s about guiding you to act in a way that gives everyone more time to respond. It’s the quiet promise of the rule: if we slow down, listen, and use what we have, we can share the water safely, even when the world narrows to a few meters of glassy gray.

If you’re curious about how this all comes together in everyday sailing, you’ll appreciate how weather continues to shape decision-making at sea. Fog isn’t just a weather report; it’s a character in the story of every voyage. Rule 19 helps you read that character with discipline, not fear.

Resources worth exploring

To deepen understanding without turning the sea into a math problem, consider these practical touchpoints:

• Basic radar operation guides from manufacturers like Furuno or Garmin

• AIS demonstrations and tutorials from national maritime authorities

• VHF radio usage basics and proper phrases under distress and safety communications

• Bridge resource management courses or simulations that emphasize teamwork and decision-making under pressure

The bottom line

Rule 19 is a practical safeguard for visibility-challenged voyages. It’s a reminder that safe navigation hinges on a blend of speed management, vigilant lookout, smart use of technology, and clear, early action. When the fog settles in, the right habits keep you moving in a way that protects you, your crew, and everyone else on the water. And that, more than anything, is what good seamanship looks like in the real world.