When is a vessel considered underway under the COLREGs Rules of the Road?

When is a vessel considered underway? It’s one of those little definitions that sounds simple until you pause and think about the edge cases. For anyone dipping into the Rules of the Road, this is one of those anchor points—pun intended—that clarifies how different vessels behave and which rules apply at any given moment.

Here’s the short answer, plain and clear: a vessel is underway when it is not grounded, anchored, or attached to shore. In other words, as long as a ship isn’t sitting on the bottom, isn’t tied to a dock or shore, and isn’t held fixed in place by any mooring, it’s under way. If you’re moored, anchored, or aground, you’re not underway. If you’re in dry dock, you’re not afloat at all, so you’re not underway either. Simple to say, but let’s unpack what that really means in practice.

The nuance behind the rule

What does “underway” really imply? It’s a status, not a moment-to-moment motion status. You don’t have to be blasting along at 20 knots to be underway. You just need to be free to navigate and respond to the helm and controls. If you’re sitting in the water, but you could move off if you wanted to, you’re underway. If you’re tied to a pier and cannot move without being cut loose, you’re not underway.

This distinction matters because COLREGs treat vessels that are underway differently from those that are stationary. For example, certain collision avoidance rules hinge on whether a vessel is underway versus anchored or moored. The same rules that govern two ships in open water shift when one of them is secured to a shore or dock. So understanding the baseline status helps you predict how another vessel should behave—and how you should respond.

What counts as not underway

• Grounded or aground: A vessel that has run aground is literally stuck on the bottom. No matter how determined the crew is to power forward, the vessel isn’t underway until it’s free of the obstruction and afloat again.

• Anchored: A ship held in place by an anchor isn’t underway. It’s fixed to the sea bottom via the anchor chain and waiting, perhaps in a holding pattern, perhaps waiting for the tide to shift, but not navigating.

• Moored: A vessel tied to a shore installation, buoy, or mooring, is not underway. It’s secured and stationary.

• In dry dock: This one is the most obvious—out of the water, no navigation, no cruising. Not underway.

A quick mental model you can use on the bridge

Imagine a busy harbor or a narrow channel. You’ve got vessels of all kinds: some moving, some barely creeping, some sitting still in the slots. The underway vessels are the ones that could maneuver if the helm were turned and the engines cranked. The stationary ones—anchored, moored, or ashore in a dry dock—serve as fixed points or obstacles in the water.

A vessel being towed is a small gray area that’s worth naming. If the towed vessel isn’t anchored, isn’t moored, and isn’t aground, it’s generally considered underway. The same goes for a tug pushing a barge or a group of vessels being moved in a controlled manner. The tug and its tow need to coordinate like dancers in a tight harbor corridor, because the rules you follow depend in part on whether the tow is moving and whether either party is anchored or fixed in place.

Why this matters for safe navigation

Knowing whether another vessel is underway directly informs your course of action. Different rules apply when vessels are underway vs when they’re stationary. For instance:

• Collision avoidance: When two ships are underway, the classic rules of the road kick in differently than when one vessel is at anchor or moored. You’ll be looking at headings, right-of-way, and whether a vector change is needed to avoid a collision. When a vessel is anchored or moored, another vessel has to respect that status and avoid unnecessary risks in an entirely different way.

• Crossing situations: If you’re underway and another vessel is also underway, you’ll rely on the standard crossing rules (which vessel is the give-way and which is the stand-on). If one vessel is anchored or moored, you treat the other vessel with different expectations because their ability to maneuver is constrained.

• Narrow channels: In tight waterways, the difference between underway and not underway can be the difference between a safe pass and a near-mmiss. A vessel anchored in a channel acts like a fixed obstacle; a vessel underway might adjust speed or course to clear a path.

Practical takeaways you can use on the water

• Start with the status check: Before you plot your course, quickly assess whether nearby vessels are underway. Do they look free to maneuver, or are they fixed to shore, in a docked position, or resting on the bottom? This snapshot guides your risk assessment.

• Treat anchored vessels with caution: Even though an anchored vessel isn’t underway, wind and current can cause the anchor to drag, and moored vessels can swing. Give them space, especially in crowded harbors or channels.

• Remember the tow dynamics: If you’re sharing the water with towing operations, watch for the tug and its tow. The tow is typically considered underway if not anchored or moored, so your collision avoidance plan should account for their potential to change direction or speed quickly.

• Dry dock awareness: When a vessel is in dry dock, it’s not part of the moving traffic flow. Still, nearby operations—cranes, floating equipment, divers—mean you should stay alert to avoid hazards.

A few real-life moments that crystallize the concept

• Picture a ferry slipping from its mooring for a routine turnaround. Once the lines are cast off and the engines hum, it’s underway. It will follow rules appropriate to moving traffic, and other vessels will adjust accordingly. If, however, the ferry hasn’t cleared the moorings and is still tied up, it remains not underway.

• Consider a small fishing boat riding at anchor in a busy inlet. It’s not underway, so other vessels should anticipate a stationary object. If a larger ship with engines running approaches, the master must plan to avoid colliding with that anchored boat or swinging lines.

• Think about a rescue vessel in a harbor that’s towing a life raft or another small craft. The towing arrangement can be underway if neither vessel is anchored, moored, nor aground, demanding a careful, predictable set of movements from both parties.

Putting the concept into everyday language

You can think of underway as “free to move.” It’s the difference between rolling down the street and parking on the curb. A car can stop where it is, switch on hazard lights, and wait; a car cruising along the road is underway. In the water, the same logic applies to vessels. If a ship has the freedom to steer and adjust course, it’s underway. If it’s fixed to something—a dock, the bottom, or the shore—it's not.

Where the definition sits in the big picture

Rule 3 in the COLREGs houses definitions that are the building blocks for every maneuver decision on the water. Understanding what counts as underway helps you interpret Rule 5 (Look-out), Rule 6 (Safe speed), Rule 7 (risk of collision), and the many other rules that guide everyday navigation. It’s not just about memorizing a fact; it’s about building a mental map of how different vessel statuses shape behavior and responsibility.

A note on the tone of navigation duties

Respect for other water users is the throughline here. The onboard mindset—staying vigilant, communicating clearly, and anticipating the moves of others—keeps everyone safer. When you know a vessel is underway, you assume there’s potential for maneuver. When you know a vessel isn’t underway, you adjust more like you would around stationary traffic, giving extra space and time.

If you’re curious about the vocabulary and the way definitions thread through the rules, here’s a handy mental check you can keep on the bridge:

• Underway: not grounded, anchored, or moored to shore; free to maneuver

• Not underway: grounded, anchored, moored, or in dry dock

That quick mental checklist can become second nature with a little everyday exposure and scenario thinking. The more you immerse yourself in real-world harbor dynamics—peak hours, weather changes, visibility conditions—the better you’ll read the water and predict how different vessels will act.

In closing, the idea behind underway is deceptively simple: it’s all about freedom to navigate. That freedom changes how other vessels behave toward you and, equally important, how you respond to them. A vessel that’s underway is a moving participant in the traffic system. A vessel that isn’t underway is a fixed reference point you must respect and navigate around with care.

So next time you’re looking at a busy chart or an approaching silhouette on the radar, ask yourself: is this vessel underway, or is it fixed in place? The answer nudges your decision-making, keeps your crew safer, and helps you respect the shared rules that keep maritime traffic orderly on the water.