Rule 20 explains when vessels must signal under varying circumstances.

Rule 20: signaling that fits the moment

If you’ve ever found yourself reading a nautical map while a foghorn bleats in the distance, you know signals on the water aren’t just decorative. They’re a living language. Rule 20 of the COLREGs is all about this: vessels must signal their presence and their intentions, but they’ve gotta do it in a way that fits the moment. One signal won’t cover every situation. The goal is clear communication, so others can adjust course, slow down, or keep their distance safely.

Let’s break down what that means in real-world terms. Imagine you’re out there with other boats, ferries, fishing craft, perhaps a barge or two. Each vessel is moving with its own plan and pace. Rule 20 nudges us toward signals that reflect that plan and pace, rather than a generic handshake that could mean any number of things. It’s about context—visibility, traffic density, proximity to other ships, and what you’re actually doing at that moment.

What “varying circumstances” really covers

Rule 20 isn’t a black-and-white checklist; it’s a mindset. Here are the kinds of moments where signaling decisions matter:

• Restricted visibility. Fog, heavy rain, or a twilight that’s flickering on the edge of perception. In those moments, signaling becomes a lifeline. The question isn’t whether you should signal; it’s which signals will reliably convey presence and intent to the other vessels around you.

• Approaching another vessel. When you’re closing in on someone else’s path, signaling helps both of you avoid surprises. If you’re turning, slowing, or changing course, the other boat should be able to anticipate your move.

• Maneuvering at anchor or in a harbor entrance. Signals here aren’t just about moving bodies of water; they’re about minimizing the risk of collisions with moored craft, pilings, or other traffic entering and leaving a busy waterfront.

• Navigating a channel or a narrow stretch. In tight spaces, every meter matters. Clear signals prevent a chain of last-second moves that could end badly for someone’s hull or for the crew.

• Traffic density and proximity. The more boats there are near you, the more precise your signals need to be. The goal is to reduce guesswork for others and buy everyone a little thinking time in a crowded sea lane.

The practical idea: signals should match the moment

A one-size-fits-all signal just doesn’t cut it. So how do you decide what to signal?

• Consider what you’re doing. Are you altering course, slowing, stopping, or simply changing your orientation in the water? Matching the signal to the action helps others interpret your move quickly.

• Check visibility and distance. If you’re two ships away in clear light, a different signal works better than if you’re in dense fog with limited sight lines.

• Think about the other vessels. A cargo ship with limited maneuverability responds differently than a small day sailer. Your signals should be something they can reliably notice and interpret.

• Stay consistent with your signals. If you’ve established a pattern for certain situations, try to keep to it so other mariners can learn your habits and predict your moves with confidence.

A few everyday analogies

If you’ve spent time driving in busy traffic, you know signals matter there too. A turn signal isn’t just a courtesy; it’s a cue that saves people from surprises. On the water, a signaling habit serves the same purpose—only it’s more nuanced because you’re dealing with a three-dimensional, moving landscape with wind, tide, and current adding layers of complexity.

Think of it as sea-speed dating. You need to give other vessels enough information to decide how to react, without flooding them with too much. You wouldn’t shout over a loud crowd when you’re trying to set up a date; you’d use clear, appropriate signals. The same principle applies when it’s your turn to communicate on the water.

What signals look like in practice

Rule 20 points to using signals appropriate to the situation, which means both sound signals and light signals have their roles. In reduced visibility, lights become especially important, and sound may supplement those lights to catch attention where sightlines are limited. In open water with good visibility, you might rely more on predictable, steady signals that reflect your intended path or speed changes.

To keep things intuitive:

• If you’re changing course to avoid a collision, your signals should clearly indicate that intention.

• If you’re entering or leaving a channel, signals should help others gauge your heading relative to theirs.

• If you must stop or slow dramatically, your signals should give others time to react.

Common missteps to avoid (and how Rule 20 helps)

Like any rule, the danger lies in assuming you know what others will understand. A few pitfalls show up again and again:

• Signaling too late. In close quarters or in restricted visibility, late signals carry a higher risk of misinterpretation and collision.

• Overloading signals. Trying to convey too many intentions at once can confuse nearby vessels. Clarity beats cleverness in the harsh light of the water.

• Relying on a single signal for all situations. Context matters, and the same signal can have different meanings based on where you are and who’s around you.

• Failing to signal at all in tricky conditions. If you’re operating in an area with dense traffic or poor visibility, skipping signals is a fast path to misunderstandings.

A simple approach you can keep in mind

• Before you move, scan the scene: what’s the traffic density? What are your immediate risks? What signals are appropriate to this moment?

• Pick a signal method that’s reliable for the conditions—sound, light, or both.

• Execute the signal early enough for others to see and interpret it.

• Confirm by watching how other vessels react; adjust if necessary.

A small, practical toolkit

Here’s a lightweight checklist you can mentally run through when you’re on deck:

• Are visibility conditions changing? If yes, adjust your signaling accordingly.

• Am I near other vessels or entering a channel? Signal more clearly and earlier.

• Is there a high chance of misinterpretation? Use extra signals to reassure other mariners.

• Do I know the signaling habits of nearby ship types? Big ships might need different cues than small craft.

Connecting the dots with everyday nautical life

Rule 20 sits right where navigation and communication meet. It’s not just about obeying a rule; it’s about being a good neighbor on the water. When you signal with intention, you’re reducing uncertainty for everyone else who shares the sea with you. And when the weather turns unsettled or the harbor turns busy, that clarity becomes a lifeline.

If you’re learning these principles, you’ll notice that many of the same ideas show up in planning, risk assessment, and even teamwork aboard a vessel. A captain’s decision isn’t made in a vacuum; it’s made with an awareness of signals, intent, and the possible responses from others. Treat Rule 20 as the navigational conversation starter that keeps that dialogue productive, even in rough seas.

A reflective moment

The sea has a way of turning small decisions into big consequences. That’s why signaling matters so much. It’s not about heroics; it’s about predictability, safety, and trust among people who operate in a shared space. When you’re listening to the water and watching the sky for signs of other boats, Rule 20 becomes less of a rule and more of a practical habit—one that makes every voyage more reassuring for the crew and the passengers onboard.

Closing thought: learning to listen as you signal

In the end, Rule 20 is a reminder that signaling is communication with real consequences. The signals you choose should reflect the actual situation, not a default plan. Whether you’re slicing through a calm harbor or threading a path through a crowded channel, the right signal helps others understand your speed, direction, and intent. And when a crew works in harmony with signals that fit the moment, the water feels a lot less unforgiving.

If you’re revisiting these ideas, take a moment to visualize a handful of common scenarios—foggy inlet, crowded harbor, open-water passage—and imagine which signals would best convey your plan in each case. The goal isn’t to memorize a rigid set of phrases but to cultivate a flexible, situational understanding. That’s what Rule 20 is driving at: signaling that’s responsive, responsible, and, frankly, a part of good seamanship.