Rule 35 fog signals: sound them when visibility is reduced or a vessel is at a standstill

Fog draped over the water has a way of turning a simple voyage into a quiet, tense game of guesswork. You can’t rely on sight alone, and that’s when rules kick in to keep people safe. One of the most practical, straightforward guidelines is Rule 35 from the COLREGs—the Rules of the Road at sea—about fog signals. So, when are you actually required to sound one? The correct answer is: when you’re constrained by visibility or when you’re at a standstill. Let me break that down, with a few real-world angles to help it stick.

Rule 35 in plain language

Rule 35 covers fog signals—those audible cues boats use when it’s hard to see. The core idea is simple: if your ability to see other vessels is hampered, you should make your presence known with a fog signal. If you’re not moving, or if visibility is restricted to the point where you can’t safely determine other vessels’ positions, you need to sound signals. The goal isn’t to irritate the seas; it’s to help others understand where you are and what you’re doing so a collision can be avoided.

What does “constrained by visibility” really mean?

• Fog, rain, snow, heavy spray—anything that reduces how far you can see or how clearly you can judge distance and bearings.

• It’s not just “foggy at night.” Reduced visibility could show up during daylight too, if the conditions are thick enough to blur the horizon and other boats.

• If you’re unsure where nearby vessels are, or if you’re unsure about their intentions, that’s a cue to sound—a living, audible beacon that you’re there.

And what about “at a standstill”?

• If your vessel isn’t moving and you’re anchored or blocked by the waterway, you still want other boats to know where you are. A fog signal helps prevent accidental contact with boats that can’t see you clearly. Standing still is a different risk profile; a signal helps everyone understand your location and status.

Why this matters for safety at sea

Sound signals aren’t a fancy touch; they’re a practical safety tool. In poor visibility, sight is compromised, and your hearing becomes a critical line of defense. A fog signal serves as a friendly nudge to others: “I’m here, I’m near your path, adjust your course or speed.” It’s a cooperative ritual that keeps traffic moving safely, even when the weather is stubborn and unpredictable.

What the signal might look like in practice

Vessels use their whistle, horn, or other approved sound devices to produce fog signals. The exact pattern isn’t carved into stone the same way everywhere, because it can vary by vessel type and local regulation. The crucial point is consistency and being audible over the surrounding noise—engine, waves, and weather. A typical approach in many situations is to emit a standard signal that clearly travels over the water, letting nearby vessels hear you and respond if needed.

A quick note on patterns and patterns’ purpose

You’ll hear terms like “prolonged blasts” or “short blasts” in manuals, and you’ll see diagrams that map signals to maneuver intentions. The important thing for most day-to-day boating is not to overthink the pattern when visibility is reduced; it’s to provide a clear, unmistakable warning that you’re present. If you’re unsure about the exact sequence for your vessel, you can rely on your equipment’s guidance, local regulations, and good judgment. The point remains: reduce risk by making sure others hear you.

Why the other options don’t fit

• A. Only when in a crowded waterway — It’s not limited to crowded spaces. In fact, it’s about any time visibility is restricted, not just in crowds.

• C. Only during nighttime operations — Nighttime is certainly a time when extra caution matters, but Rule 35 applies whenever visibility is constrained, regardless of the hour.

• D. When entering a harbor — Entering a harbor isn’t a guarantee you’ll need a fog signal. If visibility is good and traffic is clear, the signal isn’t mandated just by the act of entering a harbor. It’s about visibility and your vessel’s status, not a destination.

Practical takeaways for sailors and boaters

• Keep a vigilant lookout and be ready to signal. If you suspect others can’t see you, sound your fog signal to establish your presence.

• Treat signals as part of a broader safety routine. Use lights when visibility is reduced, maintain a safe speed, and keep a listening watch. The whole package lowers risk.

• Coordinate with others. If you hear a fog signal nearby, respond with a signal of your own if needed. Mutual awareness helps everyone adjust course and speed in tandem.

• Remember that technology helps, but it doesn’t replace human judgment. GPS, radar, AIS, and radios all aid navigation, but sound signals remain a simple, universal language on the water.

A small tangent about sea life and habits

Their approach to rules mirrors how we approach everyday life. When you can’t rely on one sense, you lean on others. On the water, that means turning up your listening and your awareness. It’s almost like driving in heavy rain on a busy road—you slow down, turn on your lights, and take extra care to project your presence to others. The ocean doesn’t care about your schedule; it cares about safety. The fog signal is just your way of saying, “I’m here, and I’m not hidden in the mist.”

Common sense with a touch of discipline

Rule 35 isn’t a quirky rule for the technically minded alone. It’s common sense dressed up in a safety framework. In practice, it’s about communicating your presence when your eyes can’t fully do the job. A simple horn blast or a carefully timed sound signal becomes the difference between a close encounter and a safe passage.

Putting it all together

So, when you’re asked to identify the correct condition for sounding a fog signal under Rule 35, the answer is straightforward: you sound when you’re constrained by visibility or when you’re at a standstill. It’s a practical rule that keeps the waterway safer for everyone, from small runabouts to freight ships that navigate by more than just sight.

If you’re curious to learn more about how Rule 35 intersects with other navigation rules, you’ll find a world of practical wisdom in the way ships communicate, maneuver, and respect one another on the water. The big takeaway is simple: in reduced visibility, make your presence known. It’s a small action with a big payoff—one that helps maintain calm, orderly flows on even the messiest days at sea.

Final thought

Boating safety blends straightforward rules with real-world judgment. Rule 35 reminds us that sound is as important as sight, especially when the world shrinks to a gray, foggy hush. By embracing this simple guidance, you’re not just obeying a rule—you’re helping to keep every voyage safer for everyone who shares the water.