A second all-around light signals that a vessel over 50 meters is anchored.

Light signals on the water aren’t decoration. They’re language. A quick flick of a bulb or a pair of glowing white disks can tell a skipper exactly what another vessel is doing, even when the sea is tossing spray in your face or fog wraps the horizon. When you’re learning the COLREGs—the Rules of the Road for ships—you quickly discover that a vessel’s lights are the best plain-language guide to safe maneuvering. Here’s the thing about a big vessel that’s anchored: it has a very specific light setup and, yes, it matters a lot in crowded waters.

Two lights, stacked like a beacon you’d see on a quiet street

Let me explain the core idea in a simple way. When a vessel is under way, it shows certain lights to show that energy, motion, and intention exist. But when a vessel is not moving, the lights tell a different story: “I’m here, I’m stationary, I’m anchored.” For vessels longer than 50 meters, the COLREGs require a second all-around white light, positioned vertically above the first, to make that status unmistakable.

That second light isn’t just a ornament. It adds a layer of visibility—literally stacked signals that a vessel is anchored and not simply stationary for a moment. In practice, pilots and mariners use it to gauge distance, direction, and urgency. Two lights in a column are harder to mistake than one light alone, especially when you’re dealing with glare, spray, or a fog layer that muffles sound and blunts sight.

A quick run-through of the alternatives

If you’re studying or testing your knowledge of the rules, you’ll see several light configurations pop up in questions. Here’s why the other options don’t fit for a large anchored vessel:

• B. A blue light on the bow. Blue lights are reserved for a handful of special cases—tugs, vessels engaged in certain operations at night, or activities that require signaling that’s not the standard anchored status. A blue bow light by itself wouldn’t convey “anchored and not under way” the way a second all-around white light does. It would risk confusion with other signaling conventions.

• C. Only the initial all-around light. One all-around white light is part of the picture, but for vessels over 50 meters, it isn’t enough by itself to convey the full status. The second light vertically above it makes the message clearer to other mariners.

• D. Flashing red and white lights. This pattern is associated with special-purpose signaling—not a regular anchored status for large vessels. It would be flagged as an unusual or hazardous signal in many contexts, which could create more questions than it answers for other boats sharing the same waterway.

The why behind the rule

So why did the authorities add a second light for bigger ships? Because large vessels have different profiles, footprints, and blind spots. A 60, 70, or 100-meter-long ship sits higher in the water, has a longer bow, and can extend a wide wash across a channel. In busy waters—think approaches to harbors, narrow straits, or busy anchorages—the chance of misinterpreting a single light increases. A second all-around light, placed above the first, helps other mariners quickly confirm: “That vessel is anchored, not underway.” In poor visibility, that tiny stacked cue becomes a crucial clue in the night’s chess game on the sea.

Think about it like street signals in a city. You know the difference between a single streetlamp and a second lamp on a taller pole nearby. The same principle applies at sea, only the stakes are higher—collisions, entanglements, and missed routes can be costly.

What this looks like in practice

Picture a busy anchorage after sunset. A large vessel rests on its anchors, lines taut, the night quiet except for the occasional gust and the slap of a wave against the hull. If you’re approaching or passing by, you’ll see not one, but two white all-around lights aligned vertically. The lower lamp is closer to the waterline; the upper lamp sits a bit higher, like a lighthouse twin. From the right distance, the arrangement reads clearly: anchor status confirmed, not under way.

This clarity is exactly what the rules aim for: reduce ambiguity at distances where you might be weaving through a crowd, entering or leaving a harbor approach, or crossing a busy shipping lane. The color is always white for these particular signals, so the contrast stands out against the black of night or the gray of fog.

A note on timing and visibility

Light signals matter most when visibility is compromised—fog, rain, dusk, or dawn. Those are the moments when a single light might blend into the background or look like a distant star rather than a clear signal. The added second light gives your presence away in a good way—no misinterpretation about your vessel’s status. It’s a practical, safety-first approach that helps keep all ships on the same mental map.

A simple mental model you can carry on deck

If you’re ever unsure about what signals to expect, memorize this rule of thumb: big ships, at anchor, show two white lights in a vertical line. If you’re seeing just one white light, you’re probably looking at a smaller vessel or a larger vessel that’s not yet signaling anchor status—but in high-traffic zones, you’ll quickly catch the pattern and keep to the safe side.

Connecting ideas: lights, other signals, and good seamanship

Light signals are part of a broader system that includes shapes, sound signals, and the overall practice of collision avoidance. For anchored vessels, there’s also the anchor chain’s presence, the vessel’s position with respect to traffic lanes, and the duty to sound appropriate signals when visibility is restricted. The lights are one slice of the picture, but a powerful one. A sailor who can read the lights at a glance has a leg up in planning safe passages, especially when the sea offers only a smear of color and darkness.

If you’re curious, you’ll find that other signal patterns have their own stories. A sailboat under sail uses a red light on the port side and a green light on the starboard, plus perhaps a white light visible at the stern. A vessel constrained by draft might use special signals if it’s engaged in a specific operation. Yet the anchored-over-50-meters rule remains a reliable, straightforward marker, a signal that helps everyone know who’s stationary and who isn’t.

A few practical tips for living on the water

• Keep a tidy bridge routine. In busy anchorage areas, someone on watch should regularly scan for the two-light pattern in low-light conditions. It’s easy to miss if you’re busy with other tasks, so a quick, deliberate check can save you from a near-mmiss.

• Practice the recognition, not just the rules. If you’re new to the waters or unfamiliar with a port’s peculiarities, take a calm moment to observe anchor signals from a distance before you venture closer.

• Use your instruments, but don’t rely on them alone. Radar and AIS can help locate vessels, but they don’t replace the human eye. Lights are a human-readable cue that complements tech, not a substitute for it.

• Talk through procedures with your crew. A quick, routine briefing about what signals mean keeps everyone aligned—especially when you’ve got passengers or trainees aboard.

A little recap for clarity

• The anchored status for vessels over 50 meters includes a second all-around white light, placed vertically above the first. This distinct signal ensures other mariners can recognize the vessel as anchored, even in less-than-ideal visibility.

• The other options—blue bow light, only the initial light, flashing red and white—either convey different operations or do not meet the specific requirement for large anchored ships.

• This signaling rule is part of a broader safety toolkit in the COLREGs, designed to reduce ambiguity and help ships pass safely through busy waterways.

A closing thought to keep in mind

When you’re navigating or simply observing the traffic around a harbor, those two white lights aren’t just “lights.” They’re a language—quiet, precise, and essential. The better you understand it, the smoother the ride becomes, and the safer everyone stays. In the end, that’s what nautical signaling is really all about: clear messages, shared responsibilities, and a seamanship mindset that keeps the water a bit more predictable, even when the weather isn’t.

If you’d like, I can walk through more signal scenarios—how a vessel under way signals its course, or what different color lights indicate in various operations. It’s all part of building a practical, rock-solid working knowledge of COLREGs, so you can read the sea as confidently as you read a map.