In restricted visibility, maintaining a safe speed keeps you in control.

When visibility drops to a eerie gray, the sea doesn’t feel like the same place. You can’t rely on the other vessels’ lines, colors, or juts-and-jolts of motion the way you can in clear weather. In those moments, the guiding principle isn’t bravado or a flashy maneuver. It’s simple, steady, and safety-focused: maintain a safe speed.

Let me explain what that actually means in practice, and why it matters so much.

What “safe speed” really means in restricted visibility

Rule 6 of the COLREGs (the international Rules of the Road) tells us to proceed at a safe speed so that you can take proper and effective action to avoid a collision. In plain language: you should move at a pace that lets you respond to hazards that you might not yet see, or that appear suddenly. It’s not about rushing or crawling; it’s about being able to stop or turn if something unexpected pops up.

Think of safe speed as a cushion. The slower you’re going, the more time you have to interpret signals, adjust your course, and stop if needed. That cushion should reflect the current conditions: how far you can see with your lights and radar, how well your engines respond, and how quickly other vessels may appear in your path.

Why this matters in fog, rain, or haze

Restricted visibility isn’t just about fog. It’s rain against glass, spray that blacks out the bow, or a night when even the shoreline looks like a memory. In those moments, you might not see a nearby vessel until it’s almost on you. If you’re cruising at full speed, your stopping distance grows, your maneuvering room shrinks, and a sudden obstacle becomes an almost insurmountable problem.

Maintaining a safe speed gives you time to:

• detect vessels with radar, AIS, or lookouts,

• interpret their likely actions (are they crossing, overtaking, or underway on a collision course?),

• coordinate your own response—slow, steer, or stop—before you have to react abruptly.

What not to do (the three common missteps)

In restricted visibility, some instincts can backfire. Here’s why the other options don’t work—and why speed up or sudden course changes can actually raise risk.

• Speed up (not a good idea): Hurrying through fog makes you less able to notice signals or listen for another vessel’s sound signals. It also lengthens braking distance and reduces your ability to react to a surprise, such as a small craft crossing your path or a buoy you can’t quite see yet. It’s the wrong kind of speed—think of it as driving with the parking brake on: you’re less responsive, not more.

• Switch off lights (dangerous). Lights are not just for visibility; they’re signals to others about your presence, course, and speed. Turning them off compounds the problem: you become nearly invisible in conditions where others rely on lights to spot you. It’s a quick way to invite a collision.

• Change course frequently (confusing and risky). Jinking around can create a moving target effect, making it harder for nearby vessels to predict your intentions. In dense traffic or poor visibility, predictable, deliberate actions are a sailor’s best friend. You want to be understood, not a mystery cruise.

How to keep that safe speed in real life

Maintaining safe speed isn’t about a single rule—it’s a bundle of practical checks and habits you weave into your watchkeeping. Here are ways to keep the pace prudent without becoming overly cautious or paralyzed by hesitation.

• Use all available tools, but don’t rely on them alone. Radar, AIS, GPS, and depth sounders are great, but even the best gadgets don’t replace a lookout. Keep a sharp eye, listen for sound signals, and cross-check what you see with what your instruments suggest.

• Set speed to match visibility. If you can only see a few hundred meters ahead, ease your speed so you can stop within the distance you can observe with your lights and radar. If the fog lightens, adjust accordingly. It’s not a fixed number; it’s a flexible judgment based on what you can perceive at that moment.

• Consider sea state and current. A choppy sea or a strong current can make steering less predictable and stopping harder. Factor those forces into your speed choice. Slower is often safer when wake and water movement could mask a nearby vessel.

• Maintain a proper lookout around the clock. Eyes and ears aren’t optional extras; they’re part of safe speed. A vigilant watch can catch things your instruments miss—a glow from a buoy, a light that should be there but isn’t, a small craft’s wake edging into your path.

• Use sound signals as a bridge to understanding. If visibility is poor, a brief horn signal can announce your presence and help others gauge your relative bearing and speed. It’s not dramatic, just practical.

• Plan for the worst, hope for the best. In dense traffic, you might choose to reduce speed further when entering a narrow channel, near a harbor, or around a busy fishing ground. It’s about giving yourself space to react if another ship doesn’t appear until the last moment.

Concrete, everyday situations to visualize safe speed

• Crossing in fog with power-driven vessels nearby: You’re approaching a crossing from a couple of miles away. You don’t know exactly where the other vessel is or what its course might be. A measured, slower pace keeps you in a safer zone until you’ve got a clearer view of the other vessel’s actions.

• Overtaking in restricted visibility: If you’re the overtaking vessel, the best course is to stay well clear of the vessel being overtaken. Reducing speed helps you hold that safe distance and respond if the other vessel changes course unexpectedly.

• Harbor entrances and channels: Entering a harbor in mist or rain is a place where the mix of traffic is high and visibility can vary. A conservative speed gives you time to interpret signals from traffic control, other vessels, and buoys, while still letting you maneuver as needed.

• Sailing vessels with limited maneuverability: A small sailing vessel might not respond to helm or engine changes as quickly as a powerboat. In restricted visibility, you slow down to avoid a collision, ready to alter course at the first sign of crossing traffic.

The human side of safe speed

Beyond the instruments and the rules, there’s a rhythm to navigating in limited visibility that comes from experience and teamwork. The crew’s shared sense of responsibility matters. When the captain signals a deliberate, calm speed and the bridge team reads the radar returns like a well-rehearsed chorus, the ship behaves as a single, coherent unit.

There’s a touch of humility that comes with the sea in low visibility. You learn to respect the fact that what you can’t see can still pose a real danger. Emotions—calm concern, focused attention, a touch of tension—are not enemies here; they’re your signals to stay present and methodical.

A quick mental model you can carry forward

Think of safe speed as the “speed of preparation.” It’s the pace at which you’re always ready to stop or alter course if something changes. It’s not about being slow for hours on end, but about staying agile, aware, and ready to respond. If you can’t picture a clear stopping distance within your current view, you’re going too fast.

A few practical reminders to end on

• Lights on, speed moderated, lookout active. That trio is the backbone of safe navigation in reduced visibility.

• Don’t chase visibility metrics alone. If you can’t clearly see an obstacle, slow down. Your instruments aren’t your only reference; your crew’s eyes matter just as much.

• Respect the other guy’s space. You may not know what your neighbor is planning, but you can plan for the possibility that they’ll do the unexpected.

To wrap it up, here’s the throughline

In restricted visibility, the right move is steady, purposeful, and safety-first. Maintain a safe speed to keep yourself, your crew, and everyone else on the water out of harm’s way. The rule isn’t a suggestion; it’s a duty to stay prepared for whatever the sea and its traffic throw at you.

If you’re out there with fog curling around the bow, you’ll know you’ve got it right when you feel a quiet confidence in your pace. You’re not racing the clock; you’re respecting the clock—and the sea—enough to move in a way that keeps everyone safer. That’s not just compliance with a rule. It’s good seamanship.

A last note for curious minds

If you’re ever unsure about how to judge safe speed in a specific situation, slow down a touch and reassess with your lookouts and instruments. The sea is generous when you meet it with patience and a clear plan. And if you’re ever sharing a watch with someone who’s new to this, a quick chat about the idea of a “safe speed” can go a long way. A calm discussion on what you can actually see, or not, often does more than any checklist gadget ever could.

So, the next time you’re threading a vessel through a veil of fog or a rainstorm, remember: slow, steady, and deliberate is not a sign of weakness. It’s the essence of responsible navigation. In the end, safe speed isn’t just about avoiding collisions—it’s about keeping the voyage itself safe, steady, and almost intimate with the water that surrounds you.