What 'in sight of one another' means in COLREGs and how it guides safe navigation

On the water, visibility isn’t just nice to have—it’s a safety tool you actually act on. When people talk about COLREGs, the Rules of the Road, and how ships steer clear of one another, that clarity starts with a simple phrase: in sight of one another. Let me unpack what that means and why it matters for anyone who spends time at sea.

What does “in sight of one another” mean?

Here’s the thing: the phrase doesn’t refer to fancy gear or distances. It’s about what you can observe with your own eyes. The correct interpretation is: vessels are able to be observed by the eye. That’s option B, plain and straightforward. It’s not about radar detection, it’s not about who’s at the helm, and it’s not a fixed mile mark. It’s about visual observation by the crew on each vessel.

Why this distinction matters in everyday seamanship

Visual sighting is the first feed in the chain of collision avoidance. If you can see the other vessel, you can gauge the risk of collision and decide on a course of action. The rules assume you have a proper lookout, using sight and hearing, so you can detect approaching traffic and respond in time. Radar is incredibly useful, but it doesn’t replace the fact that someone has to be able to see the other ship with their own eyes. The human element—seeing, interpreting direction of travel, judging distance, and communicating intentions—still plays the lead role.

Common sense, but with a rulebook backbone. If you’re in sight, you’re responsible to take action to avoid a collision if the situation calls for it. If you’re not in sight—if you can only detect something on radar or by radio or AIS—other rules still apply, but the specific “in sight of one another” phrase isn’t triggering the same set of visual-based actions. In short: sight on the eye level matters, not just on the screen.

A quick look at why the other options miss the mark

• A. Vessels can see each other by radar — Radar is a powerful tool, but it’s not what “in sight of one another” means. Visibility to the eye is the key, and radar doesn’t fulfill that requirement on its own.

• C. Only the captain can see the other vessel — Not true. If a lookout or a crew member can visually observe another vessel, that counts. The phrase is about anyone on the vessel being able to see the other ship, not about a single designated observer.

• D. Vessels are within a half-mile of each other — Distance can vary a lot. You can be farther than a mile and still be in sight if conditions are good. The phrase isn’t about distance; it’s about the ability to observe visually.

What to do when you are in sight

If you can see the other vessel, you’re in a position to act. Here are the kinds of steps that tend to follow:

• Maintain a proper lookout. Keep eyes on the other vessel and stay aware of what it’s doing, its heading, its speed, any changes in its path.

• Assess risk of collision (MARPA is a modern term for this kind of mental math: “Mutual Alert, Relative Positioning, and Action”). If there’s a risk, you adjust course or speed to reduce it.

• Communicate clearly if needed. A brief sound signal or standard radio call can help ensure both vessels understand each other’s intentions, especially in busy areas.

• Apply the rules consistently. If one vessel is crossing, crossing rules kick in. If you’re the stand-on vessel, you keep your course and speed unless you’re taking action to avoid a collision.

• Do not rely on a single cue. Daylight, glare, or rough seas can hide features that would otherwise give you more confidence. Always re-check, adjust, and re-evaluate.

A real-world feel: how this plays out in contrasting conditions

• Clear day, calm seas: You spot a tanker on the horizon. It’s moving slowly, mostly straight. You estimate its path, compare it with yours, and decide whether you’ll alter course slightly to pass behind or alongside. A quick confirmation with a radio call or whistle signal helps confirm intentions with the crew on the other vessel.

• Fog or sea smoke: The phrase still applies, but your eyes might not see as far. You’ll lean on radar, AIS, and sound signals, but you can’t rely on visual sight for the initial risk assessment. In this case, you act on the information you have, keep a generous margin of safety, and reduce speed if needed.

• Nighttime: The same rule holds. If you can plainly observe the other vessel visually, you apply the same decision framework. If you can’t, you work with the tools you have (lights, AIS, radar) and practice heightened vigilance.

How this concept threads into daily seamanship

Think of it like driving in daylight versus driving with fog. In clear conditions, your eyes give you confident, tactile information about distance, speed, and cross-paths. In fog, you switch to instruments and conservative speed to compensate for reduced visibility. The COLREGs acknowledge this reality by anchoring critical decisions in what you can actually see with the eye, not what you wish you could see with fancy equipment alone.

Common misunderstandings that trip people up

• Believing radar visibility alone satisfies the rule: Radar helps, but “in sight” means visually observable by the crew.

• Thinking sight is only about distance: It’s about whether you can observe the other vessel at all with your eyes, regardless of miles.

• Assuming sight is a one-person job: The lookout is a team effort. If anyone on deck can visually see the other vessel, that counts toward the rule’s intent.

Practical takeaways you can use at the helm

• Always maintain a vigilant lookout, both day and night. Eye contact with other vessels isn’t negotiable; it’s the baseline.

• Use your eyes as the primary detection method, then supplement with radar, AIS, and communications as needed.

• When you spot another vessel, quickly assess collision risk and decide on a course or speed adjustment if necessary.

• Communicate your intentions clearly when it helps prevent a close encounter. A short whistle sequence or a concise radio message can do wonders for cooperation between vessels.

• In poor visibility, slow down and increase the distance you keep from others. Your eyes may be unable to confirm what you need to know, and that’s exactly when extra caution pays off.

A few practical checkpoints for learners

• Do you know what “in sight of one another” means? It means the vessels can be seen with the naked eye by the crew on each vessel.

• Do you remember why radar alone isn’t enough to define sight? Because sight in rules hinges on human observation, not a screen alone.

• Do you have a mental checklist for when you’re visually tracking another vessel? Look out, assess risk, determine if a course/speed change is needed, and communicate if appropriate.

Final reflections: why this tiny phrase carries weight

The phrase sounds almost humble, but it’s a big deal. It’s a reminder that the sea’s rules are built on human perception and shared situational awareness. The moment you can see the other vessel, a set of responsible actions falls into place. It’s about safety, yes, but also about trust—trust that the other crew is watching too, and trust that your signals are understood.

If you want to keep digging into the practical side of COLREGs, you’ll find a web of scenarios where visibility dictates action, especially in busy coastlines, harbor approaches, and narrow channels. The more you internalize the idea that “in sight of one another” is about visible observation, the more naturally your responses will align with the Rules of the Road.

Key takeaways

• In sight of one another means vessels can be observed by the eye.

• Visual sighting is the baseline for collision avoidance decisions.

• Radar and other tools support safety, but they don’t replace the need to see with your own eyes.

• Good seamanship blends eye contact, tools, clear communication, and prudent actions.

If you’re curious to explore more, look into how different Rules of the Road address overlap between sight, hearing, and tools like AIS and radar. It helps to connect the dots between what you can actually see and the actions you’re expected to take. The sea rewards both clarity and calm judgment, two traits that go hand in hand when you’re keeping sight on the horizon and in sight of one another.