In a narrow channel, the vessel with a safe navigational draft keeps to the starboard under COLREGs Rule 9.

Navigating Narrow Channels: Why Draft and Safe Passage Shape the Rule

Imagine you’re steering through a squeeze of water—waterway walls brushing on both sides, a few meters of margin, and traffic that can’t help but pile up if you’re not careful. In that kind of setting, simple “who goes first?” logic doesn’t cut it. You need a rule that keeps everyone safe, predictable, and out of the danger zone.

Here’s the thing: in a narrow channel, the vessel that keeps to the starboard side is guided by a principle that centers safety and navigational certainty. The correct thinking isn’t about who is bigger, who has more power, or who’s under sail. It’s about maintaining a safe navigational route. In other words, the priority isn’t a fixed attribute of a vessel like draft or speed; it’s about the ability to navigate safely through the constricted space.

Rule 9 and the rhythm of the channel

When mariners talk about narrow channels, they’re often talking about Rule 9 of the COLREGs. This is the rule that governs vessels operating in constricted waters and near traffic separation schemes. The core idea is straightforward, but the consequences are real: stay out of the other vessel’s way, keep your course as much as possible, and take action early if there’s any doubt about collision risk. In practice, that translates to predictability. If everyone behaves in a way that other vessels can anticipate, the chance of a close call drops dramatically.

The “starboard” convention is part of that predictability. In many situations, vessels proceed with the expectation that they’ll pass on the side that makes the most sense given the channel’s geometry. However, the specific answer you provided—“the vessel with a draft that secures a safe navigational route”—gets at an important nuance: the path that a vessel can safely navigate matters. If a vessel’s draft is such that it cannot safely clear the bottom in a bend, a shallow pocket, or a tight turn, that vessel may need to adjust to keep passage safe. In that sense, the safe navigational route isn’t a mere preference; it’s a constraint that guides behavior in tight quarters.

Let me explain with a simple frame: in a restricted waterway, the goal is to minimize risk. If one vessel’s draft makes danger of grounding more likely in the upcoming stretch, that vessel has to plan a route that reduces that risk. The other vessel, seeing that, adapts accordingly. Together, they maintain a flow that’s safer for both. It’s not about who is larger or more capable; it’s about the safest possible passage given the conditions.

Draft, depth, and practical navigation

Draft—the depth of water a vessel requires to float without touching the bottom—plays a surprisingly big role in narrow channels. You might think “bigger draft means you go last,” but that’s not the full story. The real question is: can you chart a path through the channel without forcing a risk of grounding or collision? If your ship’s draft dictates a broader, safer route through a bend or a stretch where the water is shallow, your navigational plan must reflect that reality.

This is where the art of seamanship shows up: peering at the chart, checking tidal ports, noting recent depths, and communicating with the other vessel if there’s any uncertainty. It’s not glamorous, but it’s essential. The captain who understands the “safe route” concept isn’t bragging about dredging or depth charts; they’re making decisions that protect the crew, the vessel, and everyone else on the water.

A moment’s digression—traffic schemes and the bigger picture

Narrow channels often sit near traffic separation schemes, where the flow of vessels is organized like lanes on a road. These schemes aren’t just bureaucratic lines on a chart; they’re practical guides that reduce the number of risky encounters. If you’re approaching from a bend or a constricted mouth, following the scheme’s direction and keeping to the starboard side, as applicable, creates a steady rhythm that other mariners can anticipate.

If you’ve ever watched a harbor tug guide a container ship through a tight lock, you’ve seen this principle in action. The bigger ship’s blind spots are limited; the tug acts as a speed regulator and a safety net, ensuring that the passage remains smooth. In these moments, the idea of a “safe navigational route” isn’t abstract—it’s a live, breathing plan.

Why the other choices miss the mark

Let’s talk about the common temptations. The multiple-choice options you referenced—A, B, C, and D—are useful to contrast, because they reveal why the actual rule matters.

• A: The vessel with the smallest draft. It’s tempting to think smaller is always safer in confined spaces, but in reality, draft isn’t the sole compass for safety. A small draft could still be in a tricky position if the channel curve or traffic demands a different approach.

• C: The least powered vessel. Power matters for maneuverability and stopping distance, but “least powered” isn’t a universal signal for who should yield or who should stay to starboard. It depends on the channel’s geometry, depth, currents, and the other vessel’s characteristics.

• D: The vessel under sail. Sailing vessels have their own rules of right of way in many contexts, but in narrow channels the core issue is safe passage. Sailing status alone doesn’t automatically grant priority; it’s about maintaining safety and avoiding a collision.

• B: The vessel with a draft that secures a safe navigational route. This is the one that nudges us toward a practical truth: in tight water, the decision isn’t simply about size or propulsion. It’s about whether the vessel can navigate the channel safely without forcing a hazardous situation. That safety-focused lens aligns with Rule 9’s aim: to prevent collisions by promoting predictable, prudent behavior.

Practical tips for handling narrow channels

• Check depth and tides before you enter. If you’re on a vessel with a deeper draft, plan your approach carefully. If the channel narrows or the bottom shoals, you may need to alter speed, heading, or even wait for a better moment.

• Communicate early. If there’s any doubt about the other vessel’s intentions, use appropriate signaling and, if possible, radio or bridge-to-bridge communication. Clarity reduces the risk of misinterpretation in a tense moment.

• Look ahead, not just at the bow. The current, wind, and shallow pockets can change quickly in a narrow channel. Try to anticipate the other vessel’s path, and keep a buffer zone that feels comfortable to you and your crew.

• Maintain a steady, predictable course. Sudden, erratic moves are precisely what lead to collisions in tight spaces. If you must adjust, do so smoothly and clearly.

• Know when to yield and when to stand your ground. Sometimes the best move is to slow down and let the other vessel pass, especially if you’re unsure about the depth or the other vessel’s maneuverability.

A touch of everyday relevance

Narrow channels aren’t just marine trivia. They echo moments on land too—the way we navigate tight streets during a city festival, or how we coordinate cars in a congested tunnel with a single-lane ride through. The principle is similar: safety comes from predictable behavior, from choosing a path that reduces risk, and from communicating clearly so everyone can read the plan.

As you think about Rule 9, you might also notice how technology helps. Modern ships carry depth-sounding gear, GPS-based charts, and AIS that lets nearby vessels see you on their screens. These tools don’t replace good judgment; they illuminate it. A smart navigator uses both the human instinct for caution and the machine’s precision to keep things running smoothly.

Bringing it all together

So, in a narrow channel, who should keep to the starboard side? The best way to frame it is this: the vessel that can secure a safe navigational route—taking into account depth, turning geometry, currents, and the other vessel’s capabilities—should be the one that guides the maneuver. The starboard side convention helps create a shared expectation, but the crux is safety. When depth and channel geometry push you toward a different path, that knowledge becomes the guiding light.

If you’re studying COLREGs for real-world mariner life, this isn’t just theory. It’s a practical lens you’ll use time and again—especially in the world’s narrowest waterways, where the margin for error is tiny and the consequences are real. A steady hand, a clear plan, and an eye on depth charts will serve you well.

A final thought to carry forward

Next time you’re charting a route or watching a ferry slip through a constricted passage, ask yourself: what makes this passage safe right now? Is it the vessel’s draft, its power, its sail status, or something more situational—the need to keep to a path that ensures safe navigational routes for everyone involved? The more you tune into that question, the more natural the Rule 9 mindset becomes. And that, in the end, is what helps every mariner arrive safely at the next harbor.