Two short blasts followed by a long blast in COLREGs means passing on the port side.

Decoding a Port-Side Pass: How a Simple Sound Signal Keeps Vessels Safe

Picture this: a busy waterway, fog curling along the surface, and the sound of distant engines blending with a few horns in the mix. In those moments, clear communication isn’t a luxury—it’s a lifeline. That’s where COLREGs sound signals step in. They’re the language sailors use when screens and radios can’t cut through, or when visibility is tight. Today we’re zoning in on one signal, what it means, and how everyone on deck should respond.

What the signal really says (and why it matters)

Here’s the gist: the signal made up of two short blasts and then a long blast, often described in the shorthand as two short, followed by a long, communicates a specific intention. In plain terms, it tells another vessel that the signaling boat intends to pass on the port side. In other words, it plans to keep its left side close to the other boat and pass to that vessel’s left.

This is not just trivia for a test or a quiz on rules. It’s live, real-world navigation shorthand that reduces the chance of a collision in crowded waters, poor light, or a tricky coastline. When you hear that pattern, the ten-mile-per-hour blur of a harbor can suddenly feel a lot calmer, precisely because everyone involved shares a common understanding of what’s about to happen.

Two short blasts, then a long blast: what the sequence communicates

Let me explain with a quick mental image. Two quick blasts signal a plan to maneuver to the left. Then comes the longer blast, amplifying that intention so it’s unmistakable to the other vessel. The upshot: the signaling boat is saying, “I’m going to swing my bow toward your port side and glide past you on that side.” The other vessel should acknowledge this, adjust course if needed, and keep a lookout for what’s ahead.

Why “port side pass” is a big deal—and a good rule of thumb for skippers

Every mariner grows up with the idea that “port” is the left side and “starboard” is the right. It’s one of those nautical basics that sticks because it’s practical. When you’re close in, visibility is limited, or speeds are modest, using a predictable set of signals helps prevent misinterpretations. If you’re passing on the port side, the boats stay on a predictable line, and the risk of a close-quarters tangle drops.

In real life, you’ll see this signal used in tight channels, around bends where lines of sight are short, or when a vessel is overtaking another and wants to keep space on the left before completing the maneuver. It’s a simple, efficient code that keeps the waterway flowing with fewer surprises.

How to listen, respond, and stay safe

Hearing a signal is only half the job. The other half is responding in a way that keeps everyone moving smoothly and safely. Here are practical steps you can translate into action if you’re on watch:

• Confirm what you heard, quickly but clearly. If you’re unsure about the other vessel’s intention, you can respond with a consistent signal of your own or use a radio channel to clarify. In busy spots, a light touch on the VHF can prevent misinterpretations that lead to abrupt maneuvers.

• Look and plan. Break out of the tunnel vision for a moment—check the bearing of the signaling vessel, its distance, and your own speed. Decide whether you need to adjust course, slow down, or hold steady to keep a safe clearance.

• Maintain situational awareness. Even after hearing the signal, keep a careful lookout for other traffic, changing weather, or the possibility that another vessel hasn’t yet seen you.

• Communicate ongoing intentions. If the situation evolves, keep the channels open. A follow-up signal or a quick radio message can prevent doubt from creeping in as you two (or more) boats negotiate the pass.

• Don’t rely on a single cue. Signals are crucial, but they aren’t the sole source of truth. A radar blip, a visible wake pattern, and the other vessel’s movements all add up to a complete picture.

A moment to think about shared space on the water

Waterways aren’t silent libraries; they’re dynamic stages where speed, wind, tide, and traffic all perform at once. The port-side passing signal is a reminder that the sea is a shared space. When one vessel commits to a path—port side, in this case—the others should adapt, not resist. This shared choreography is what prevents the kind of near-misses that make sailors mutter about fog and frustration rather than celebrate a clean execution.

Digress a bit: life on the bridge, and why signals matter beyond a single maneuver

If you’ve ever steered a vessel through a busy harbor, you know the moment a signal cuts through the noise like a clean line through a dense fog. It’s not just about following a rule; it’s about trust. A familiar sound pattern lets crews on all sides of the channel read the same weather of intention. In calm seas, you might feel like you’re gliding; in chop or breeze, you lean on those shared signals to keep your mind on watch, not on guesswork.

And yes, even in calmer waters, the language matters. A well-timed signal can ease a tense situation at dusk when the last light fades and every helm seems to demand attention. You don’t need bells and whistles to feel confident—just a steady habit of listening, confirming, and acting in step with others who share the same code.

A quick reference you can tuck in your mind

• Port side pass signal: two short blasts followed by a long blast, indicating the signaling vessel intends to pass on the port (left) side.

• What to do next: acknowledge, adjust if needed, and keep a watchful eye on both vessels’ course and speed.

• Why it’s important: it reduces the chance of collision in close quarters or restricted waters by providing a clear, mutual plan.

Keeping it practical: a few more pointers

• Practice with your crew. If you regularly work with others, run through a quick mental checklist of common signals and expected responses. It’s amazing how much smoother operations become when everyone’s operating from the same page.

• Use all the senses available. Sound signals are just one layer. Combine them with radar, AIS, visual bearings, and communications gear to form a robust awareness of your surroundings.

• Stay adaptable. Signals help, but weather, traffic density, and vessel performance can shift fast. If you sense a risk of misread, slow down or reposition earlier rather than later.

• Respect the margin. Even when you think you have a clear plan, leave space for human error on the other vessel—especially in low visibility or busy channels.

From signal to safe passage: a closing thought

The two short blasts and a long blast aren’t just a line in a rulebook. They’re a practical tool that ships rely on to move smoothly through shared water. When a boat on your starboard horizon signals its own maneuver, you’re not just listening for a number or letter—you’re reading an intention that has real consequences for people, hulls, and schedules.

If you’re curious to learn more, you’ll find that other signals work the same way: a concise vocal cue, a shared expectation, and a moment of calm that follows. The COLREGs aren’t about constraining freedom on the water; they’re about preserving it—by making sure everyone can predict what’s next and steer accordingly.

So next time you hear that pattern of two short blasts and a long, give a nod to the crew on the other vessel and the quiet trust that keeps the sea from turning into a lottery. The signal does the talking, but the real work—watch, plan, act, and communicate—happens on deck. And that, more than anything, is how seamanship stays human, even when the boats are moving at speed.