Rule 18 explains the obligations of vessels constrained by their draft and fishing vessels.

Rule 18 and the Sea’s Gentle Give-Way: CBD Vessels, Fishing Boats, and the Kind of Clear Rules That Keep Everyone Safe

Picture this: you’re steering a small boat along a busy coastline. A big cargo ship glides past, a fishing vessel hauls its nets, and a tugboat nudges a barge through a narrow channel. In moments like these, you want to know who yields, who keeps their course, and how to stay out of trouble. That’s where Rule 18 of the COLREGs—the International Rules for Preventing Collisions at Sea—steps in. It’s not a flashy rule with dramatic maneuvers; it’s a practical, sober set of obligations designed to keep the water calm and predictable when certain kinds of vessels are limited in what they can do.

What Rule 18 Actually Covers

Let’s break it down in plain language. Rule 18 is all about responsibilities between vessels and it places special emphasis on a few categories that behave differently on the water:

• Vessels constrained by their draft (CBD): These are ships so large or heavy that their depth in the water limits how quickly they can maneuver. Think of a big freight vessel trying to twist through a shallow channel or maneuver near a crowded dock. Because they can’t easily turn or stop, Rule 18 asks other vessels not constrained by draft to be especially mindful and to take appropriate steps to avoid collisions.

• Fishing vessels: A boat engaged in fishing has its own routine—nets, lines, gear in the water, and a tendency to move in ways that aren’t as predictable as other ships. Rule 18 recognizes that fishing vessels can’t always “step aside” the way a fast motor yacht might, so it sets expectations for how nearby vessels should behave to prevent accidents.

• Vessels not under command (NUC) and vessels restricted in their ability to maneuver (RAM): These are the other ships that can’t easily maneuver either—maybe due to mechanical trouble (not under command) or because their operations are constrained (RAM). Rule 18 ties together all these situations to create predictable patterns of yielding and passing.

In essence, Rule 18 is a governance guide for “special cases” on the water. It’s about preventing collisions by clarifying which vessels must give way and under what circumstances. It’s not about one-size-fits-all rules; it’s about acknowledging the realities of ships with limited maneuverability and the practical duties of nearby vessels to keep clear.

Why This Matters: Predictability in a Busiest of Environments

Waterways aren’t empty lanes. They’re dynamic, crowded, and sometimes noisy with the hum of engines and the chatter of VHF radios. When CBDs and fishing vessels share the same stretch of sea, the plain, predictable behavior of all parties becomes a lifeline. If you’ve ever watched a large vessel slip through a crowded harbor, you’ll notice something essential: there aren’t fancy stunts or dramatic evasive maneuvers. There’s steady, deliberate behavior—reduced speed, earlier signaling, extra room to maneuver, and, when necessary, a clear change in course.

Rule 18 isn’t about complicated tricks. It’s about setting a sensible boundary between vessels with different capabilities. If you’re operating a small boat near a CBD ship or a fishing boat, you’re not asking for trouble by staying out of a ship’s blind spots or by giving them extra space when they’re showing signs of constricted maneuverability. It’s simply good seamanship—knowing when to yield, when to keep your course, and how to communicate your intentions clearly.

A Real-World Mental Model

Could you imagine driving through a busy intersection where some drivers can’t accelerate or steer easily? Streets let you know who might drift or stop unexpectedly; you slow down, give a little extra space, and stay ready to adapt. The same logic applies at sea. CBDs and fishing vessels act a bit like those slower, heavier cars in a tight city block. The other vessels on the scene—whether it’s a nimble sailboat, a fast motorboat, or a rescue craft—carry the responsibility to adjust. That’s Rule 18 in practice: it’s about shared responsibility and safer passage through the areas where maneuvering isn’t as forgiving as you’d wish.

How to See Rule 18 in Action on the Water

• Identify the players: Look for CBDs—ships that are known to have limited ability to maneuver because of their size and draught—and for fishing vessels at work. They don’t always advertise their status with big signs, but you can often recognize the telltale signs: large hulls, set operating gear in the water, or signals indicating fishing activity.

• Expect extra caution near them: When you’re approaching or passing a CBD or a fishing vessel, you’ll want to slow down earlier, keep your bearings, and communicate clearly if you need to adjust your own course. The goal isn’t drama; it’s predictability.

• Use all your tools: AIS, radar, and good radio communication help you read the scene. If you can, plan your approach so there’s ample room for a CBD or a fishing vessel to maneuver safely. In close quarters, even a small deckhand’s glance can be enough to avert misreads.

A Little Tangent That Helps with the Mood (and the Math)

Sometimes it helps to connect navigation rules to everyday experiences. Imagine you’re crossing a busy street with a big, slow-moving truck at your side and a cyclist zipping by in the lane beside it. You don’t race the truck; you give it more time to move, you eye the cyclist’s path, and you move in a way that keeps everyone safe. On the water, CBD and fishing vessels function similarly in their own language of signals and space. You may not hear a blinker, but you’ll see a light, you’ll hear a horn, and you’ll feel the rhythm of the water telling you to adjust your pace and direction.

What That Means for a Practical Seafarer

If you’re steering a small craft near CBDs or fishing boats, here are a few concise reminders tucked into Rule 18’s spirit:

• Yield when required, but do so early. If a larger vessel has restricted maneuverability, give it the room to move in its own time. Don’t wait until the last moment to react.

• Keep a clear course only when it’s safe to do so. If your chosen path could force a CBD or a fishing vessel into a risky maneuver, consider adjusting your own course sooner rather than later.

• Be explicit in your intentions. Use sound signals or radios when appropriate, so everyone understands what you’re doing next.

• Don’t assume a vessel’s intentions. Rules are about behavior under typical conditions, but the sea can surprise you. Always be ready to adapt.

• Think in terms of “stay clear” and “give way.” The language of Rule 18 is about avoiding close quarters and ensuring predictable movement, not about showing off fancy maneuvers.

A Quick Check-In: The Question Reframed

Here’s a short, real-world-styled prompt you might encounter when thinking through Rule 18:

Question: What does Rule 18 specify regarding vessel obligations?

• A. It outlines responsibilities for all vessels

• B. It details obligations for vessels constrained by their draft and fishing vessels

• C. It applies only to commercial vessels

• D. It specifies maneuvers for recreational vessels

Answer: B. It details obligations for vessels constrained by their draft and fishing vessels. The tidy truth is that Rule 18 zeroes in on those two categories (CBD and fishing vessels) and also notes the duties of vessels not under command and RAM. The point is simple: when a vessel can’t move easily, others around it must be extra mindful to prevent collisions.

A Circle Back: Why the Nuance Matters

You might wonder why there’s a rule that seems to apply to a narrower slice of ships. The reason is practical safety. In the real world, ships aren’t just ships—they’re systems: engines, cargo, lines, nets, crew, and sometimes even weather. CBDs and fishing vessels operate with constraints that can’t be ignored. Rule 18 provides a safety net by clarifying expectations for those scenarios, so everyone can navigate with better predictability.

If you’re curious to learn more later, you’ll find Rule 18 sits within the larger framework of the Rules of the Road. The other rules handle the big scenarios: head-on situations, crossing paths, overtaking, and general safe speed. Rule 18 complements those rules by speaking specifically to the vessels whose speed and maneuverability aren’t as flexible.

Practical Takeaways You Can Carry Aboard

• Know who counts as CBD and fishing vessels. If you’re near a large ship or a boat with gear in the water, assume it may not be able to maneuver quickly and give it extra space.

• Communicate clearly. Use standard signals and, when appropriate, radio calls to confirm your intentions before making a move.

• Plan your pass with room to spare. Don’t squeeze by in tight quarters; the margin for error is smaller for CBDs and fishing boats.

• Keep an eye on the weather and currents. These factors can amplify the limitations of maneuverability and tilt the balance toward extra caution.

• Treat Rule 18 as a guide to cooperation, not competition. The sea asks for teamwork, and Rule 18 is basically a polite invitation to yield when it’s sensible.

Closing Thoughts: Rules that Quietly Save Lives

Rule 18 may sound technical, almost like a footnote in a big manual. But it’s one of those practical rules that quietly does a lot of heavy lifting. When you’re out on the water, safety often rides on the edges—on how early you slow down, how clearly you signal, and how thoughtfully you read a vessel with restricted ability. CBDs and fishing boats aren’t drama-makers; they’re part of the fabric of the sea. Rule 18 helps knit that fabric together so that every voyage can be smoother, safer, and more predictable.

If you ever want a refresher, the key thread to remember is simple: in rules and in life, some vessels need more space. When you acknowledge that, you’re already a step closer to better seamanship and safer passages for everyone on board. And that’s a win for any captain, anywhere on the globe.