Rule 18: When Vessels Are in Sight, Take Action to Avoid Collisions

Rule 18 and the Dance of the Water: Why Vessels Must Take Action to Avoid Collision

If you’ve ever watched two boats glide toward one another on a bright day, you know there’s a moment when everything changes. The mood shifts from “looks clear” to “we’ve got to do something.” That moment is at the heart of Rule 18 of the COLREGs—the part that deals with vessels in sight of one another. In plain terms: when other vessels are visible, you must take action to avoid a collision. No guessing, no hoping the other boat will move first. Proactive, decisive judgment is the name of the game.

Let me explain what that means in everyday navigation. Rule 18 isn’t just a polite suggestion; it’s a duty. It recognizes that visibility creates a shared responsibility. The more you can see, the more you’re expected to do to keep the waters safe for everyone on board. It’s the maritime version of “if you see a problem, fix it,” only with more consequences if you don’t. And yes, it applies whether you’re skimming along a busy harbor, threading through a crowded channel, or cruising past a fisherman who’s got his gear out and about.

What exactly does “take action to avoid collisions” look like in practice? The rule centers on positive action—clear, timely, and deliberate moves that reduce risk. Here are the core ideas in approachable terms:

• Change speed: If you’re approaching a potential conflict, slowing down can create the necessary space and time for safe passing. It’s the easiest first move, especially if you’re not sure of the other vessel’s intentions.

• Alter course: A small, well-planned change in direction can prevent a near-mmiss from becoming a collision. The key is to do it early enough that the other vessel isn’t surprised, and with enough clearance to be confident in your new path.

• Use a combination: Often, a mix of small course changes and speed adjustments works best. The goal isn’t a dramatic maneuver; it’s a smooth, predictable adjustment that keeps both ships out of harm’s way.

• Communicate when needed (safely): In some situations, using sound or light signals can help convey your intentions if there’s any doubt about what you’re about to do. Clear communication helps both vessels align their actions.

Now, you might wonder: does Rule 18 tell me exactly who should move when two boats approach head-on, or who should yield in a crossing? That’s where the beauty—and the complexity—of the COLREGs comes in. Rule 18 sets the expectation for both vessels to act to avoid danger, but the precise actions are guided by the more specific rules for particular situations (for example, crossing, head-on, or overtaking). The long and short of it is this: when you can see another vessel, you’re not a passive observer. You’re a participant in a shared responsibility to stay safe.

A quick mental model helps. Picture the other boat as a partner in a safety duet. If you don’t raise your voice (i.e., signal your intentions) or move in a way that’s predictable, the duet can stumble into a clash. If you do take decisive action—earlier rather than later—the scene remains calm and controlled. That’s the essence of Rule 18: proactive, responsible navigation based on what you can observe and anticipate.

Real-world feel and why it matters

Rule 18 isn’t just a rule for the abstract. It’s your daily compass when you’re maneuvering in traffic, maneuvering around moorings, or negotiating a busy canal. It’s also a reminder that safety isn’t a solo performance. It depends on awareness, good seamanship, and timely decisions.

Think about a small sailboat crossing a busy channel with a power-driven vessel bearing down from the starboard side. The rule of the road says there should be a predictable, safe plan. If both boats wait for the other to move, that’s when trouble can fester. If the sailboat reduces speed a touch and establishes a clear course to pass behind the larger vessel, the risk dwindles. The other party may adjust as well. The result is a smoother, safer passage for everyone aboard.

On the water, conditions aren’t always friendly. Visibility can be limited by glare, rain, fog, or a crowded harbor with lots of little boats. Rule 18 acknowledges reality: you’ve got to act when you can see the other vessel, not wish for the other vessel to act first. It’s a practical discipline, not a polishing of ideals.

Common misunderstandings that sailors sometimes stumble over

• “I can see them, so I’ll just maintain course.” This feels like confidence, but Rule 18 is clear that visibility brings responsibility. If there’s a risk of collision, you should consider a course or speed adjustment rather than assuming the other vessel will do what you want.

• “If they’re on my starboard side, I have the right of way.” The COLREGs are not about rights in the sense of winners and losers; they’re about safe outcomes. Even if you think you have the right of way, taking early action to avoid a collision is prudent. It reduces the chance that the other vessel misreads your intentions.

• “Sound signals are only for big ships.” Sound signals are tools for all vessels when there’s doubt or poor visibility. Don’t wait for a large vessel to respond—clear, timely signaling can reduce ambiguity for everyone.

A few practical tips for navigating Rule 18 in the wild

• Keep a wide look-out. Your best tool is a sharp, constant watch. It’s easy to drift into a routine, especially in calm conditions, but a vigilant lookout catches things early.

• Use speed controls thoughtfully. Hard braking isn’t always possible, but easing off the throttle or slowing gradually can provide the space needed to maneuver safely.

• Practice predictable maneuvers. If you decide to alter course, do it with intention and in a way that other vessels can understand. Smooth, deliberate actions beat abrupt, surprising moves every time.

• Don’t get tunnel-visioned by your plot. Scan not just for other vessels but for potential hazards—fishing gear, buoys, swimmers, or anchored craft. A wider view pays off when you’re trying to avoid collision.

• Know the caveats. There are rules that apply differently in channels, narrow passages, or near traffic separation schemes. Rule 18 sits within a bigger framework, so it helps to know where other rules kick in.

A quick, reader-friendly way to remember it

• Rule 18 is about responsibility when you can see another vessel.

• The core duty: take positive action to avoid collisions.

• Action = adjust speed, alter course, or both—early and clearly.

• It’s a teamwork mindset: you’re part of a dynamic, interactive flow of safe navigation.

Connecting the dots to everyday life

If you’ve ever driven in heavy traffic or navigated a crowded roundabout, you’ve felt a similar pressure: act with awareness, communicate clearly, and adjust your movement to keep the flow smooth. The water isn’t so different. The only thing that changes is the medium and the potential consequences. On land, a sudden lane change might irritate someone. At sea, a late move can end badly for people and property. Rule 18 translates a core principle—use what you see to steer toward safety—into an action plan you can live with on the bridge, at the helm, or in the cockpit of a small craft.

Bringing it back to the bigger picture

Rule 18 isn’t a single action, but a philosophy: when you can see another vessel, you should act to avoid collision. It’s not about proving who’s in the right or who has the most impressive engine. It’s about steady, proactive navigation that keeps people safe and ships unharmed. The rest of the COLREGs then fine-tune the exact moves for particular situations, but Rule 18 sets the tone: don’t wait for danger to arrive—shape the safe outcome with your choices.

If you’re curious about how this plays out in different environments, you’ll find that harbor pilots, commercial ships, and recreational sailors all rely on the same principle. It’s a shared language of safety. And like any language, the more you use it, the clearer it becomes.

So, next time you’re out on the water and you can see another vessel, pause for a moment. Look, assess, and act with purpose. A small change in speed or direction now can avert a big disaster later. That’s the heartbeat of Rule 18: take action to avoid collisions, and keep everyone moving toward a safer horizon.