Vessels at anchor must display lights and shapes under COLREGs Rule 27 to stay visible

Outline to guide you

• Why anchored vessels signal their status

• Rule 27 in plain terms: lights and day shapes

• The exact lighting setup, by ship size

• The day shape: the ball

• Why this signaling matters for everyone who shares the water

• Quick, practical takeaways for mariners

• A light-hearted nod to real-world navigation moments

Anchored status and the signal you can’t miss

Picture a quiet harbor at dusk: a beached silhouette, a gentle sway with the tide, and a ship that’s settled in for a spell. Even in calm waters, you need clear communication with others on the water. The COLREGs—those international rules that keep everyone moving safely—spell out what vessels must do to show they’re at anchor. The goal is simple: tell approaching vessels, “We’re not moving; we’re waiting here.” That prevents collisions and makes life on the water a lot less stressful for skippers and crews alike.

Rule 27 in everyday terms

Rule 27 is the anchor-signaling rule. It boils down to two big visuals: lights and shapes. When a vessel is at anchor, it must display a specific white anchor light. If that vessel is longer than 50 meters, it must also show a second white light toward the bow. And during daylight hours, it should display a ball shape to make the status obvious even when the lights aren’t shining.

This isn’t just about ticking boxes. It’s about a shared, universal language on the water. You don’t need to read a book to understand what another ship is signaling—you just need to know where to look. The lights do the talking when visibility is low; the day shape fills in the message when the sun is up. It’s a small setup with a big impact.

The exact setup, step by step

• One white anchor light at the stern: This light is visible from behind and to the sides, signaling that the vessel is anchored and not making way. It’s a bright, white sentinel that tells following vessels to expect a stationary target.

• A second white light at the bow for ships over 50 meters: For larger vessels, the bow light ensures the status is clear from the forward arc as well. Think of it as your front-facing confirmation that the ship is anchored.

• Day shapes: A ball shape during the day: The ball is a simple, universally recognized marker that conveys “anchored” even without lights. You’ll see it fluttering in the sun or marking the side of the deck as a quick visual cue for anyone nearby.

• Where to place and how to see them: The stern light sits toward the rear, while the bow light (if required) sits toward the bow. Both lights flash or glow steady, depending on the vessel’s setup, but the key is visibility in all directions as much as possible.

A quick digression that helps the memory stick

If you’ve ever watched boats drift past a marina at night, you might have noticed how those white lights look almost like a little lighthouse in a crowded harbor. The rule isn’t asking for drama or flair; it wants clarity. The lights are a fixed, predictable signal you can count on—no guessing games when the weather turns or when another vessel comes rushing up from a blind bend in the waterway. And yes, for the days when the sun is bright and the breeze is calm, that day shape—the ball—keeps the signal obvious, even if the lights are dimmed by glare.

Why this matters: safety on the water

Anchors are a common sight in busy waterways, harbors, and anchorages. A vessel settled at anchor can be unexpectedly affected by currents, wind shifts, or the actions of other ships maneuvering nearby. Clear signaling helps reduce the risk of wrong-way movements, near-misses, and tangled situations. When you’re learning the COLREGs, recognizing Rule 27 signals is like recognizing a traffic sign from a distance: it gives you lead time to adjust your course, reduce speed, or pass with care.

Common questions and subtle misconceptions

• Does every anchored vessel need a light at night? Not every vessel must, but the rule states a white anchor light at the stern, with a second if over 50 meters, plus the day ball sign. It’s about standardization so other mariners can interpret the signal quickly.

• Can a vessel at anchor use a loud horn to indicate its status? A horn can be used for various signals and warnings, but it does not replace the mandated lights and shapes for showing an anchored status.

• What about smaller boats or kayaks? Smaller craft still follow the same principle for the night signal, but sizes and exact carriage may vary with local regulations and vessel types. The essential idea remains: make your status obvious to others who might be around you.

• If you see no lights, does that mean no signal is required? Not necessarily. Darkness, fouled lights, or signaling failures complicate the picture. In those cases, additional measures—like reducing speed and making careful observations—are critical, and you should treat the situation as a potential risk until you’re sure of the status.

Tips you can use on the water

• Always scan for anchor signals when you’re entering busy waters or approaching a harbor entrance, especially at night or in poor visibility.

• If you’re responsible for a vessel over 50 meters, plan your signaling plan ahead: ensure the bow light is operable and clearly visible along the intended arcs.

• In daylight, rely on the ball shape as your anchor-status cue. Don’t assume that the absence of a ball means you’re not anchored.

• Practice the habit of cross-checking signals with AIS and radar where available. While signals give one form of information, modern navigation tools provide complementary context.

Relatable examples and real-world sensations

Think of Rule 27 like a parking brake sign on a busy city street—but underwater. When a car is parked, you know it’s not moving. In the water, a ship signaling anchor status does the same job. The bow light says, “We’re here but not going forward,” and the stern light confirms the same from behind. The ball during the day is the friendly ribbed patch of signage you’ll spot from a distance when the light is not in play or when you’re cruising past in daylight. It’s a simple triad—two white lights and a ball—that keeps a lot of boats from bumping into each other.

Bringing it together: what you should remember

• Rule 27 centers on lights and a day shape to mark a vessel as anchored.

• The stern gets a white anchor light; a large enough vessel (over 50 meters) adds a white light at the bow.

• By day, the ball shape acts as a robust, readable indicator.

• This signaling helps everyone keep safe, especially in crowded waterways or tricky weather.

A final thought before you go

If you ever find yourself at the helm near a harbor, take a moment to scan for those anchor signals. They’re tiny cues, but they carry big meaning. Lights blink; the ball hangs up high or marks its presence in the daylight; and with that, a network of navigation confidence forms between vessels. The sea is a shared space, after all, and these little signals are how we all say, “I’ve got this handled, and I’ll meet you around the bend.”

In short: what must vessels do to indicate they are at anchor? They display one white anchor light at the stern, and a second white light at the bow if the vessel is over 50 meters long, plus a ball shape during the day. It’s a straightforward rule, but like any good rule, it earns its keep by keeping the water safer for everyone who uses it.