Vessels should use all available means to determine the risk of collision.

Outline (skeleton)

• Opening: Why collision risk assessment sits at the heart of safe navigation and how the COLREGs push us to use more than one tool.

• The one-tool myth: why relying on sight alone or radar alone can miss something important.

• The toolbox you actually need: visual cues, radar, AIS, sound signals, VHF, charts and electronic plotting, and crew communication.

• A practical approach: a simple, repeatable method for evaluating collision risk in any situation.

• Common traps: over-relying on one source, misreading data, ignoring unusual traffic patterns.

• Takeaway: embrace the mindset of “all available means” and keep drills part of the routine.

From one glance to a safer voyage: using all available means to judge collision risk

Let’s talk about a core idea that sits at the center of the Rules of the Road. When vessels share crowded waters, the big question isn’t “Is there another ship nearby?” It’s “What’s the risk that we’ll collide, and what should we do about it?” The answer, embedded in the COLREGs, is simple in spirit and powerful in practice: use all available means appropriate to the circumstances. In plain terms, don’t rely on one tool to tell you what the others already know. Combine what you see, hear, and measure, and weigh it against what you know about how ships move.

The one-tool myth: why you can’t rely on sight or radar alone

Think about this: sight can be great in clear weather, but it betrays you at night, in fog, or when glare makes a distant light hard to read. Radar is excellent for detecting objects you can’t pick up visually, especially in low visibility or at night. But radar has its blind spots too—small vessels, choppy seas, and certain materials or weather conditions can obscure returns. AIS can reveal a lot about nearby ships, like their course and speed, but it isn’t a guarantee. We don’t always receive AIS data, or it can be spoofed or outdated. And there’s a human factor: data is only as good as the interpretation behind it.

So the best approach isn’t to put all faith in one signal. It’s to cross-check: what does visual observation say? What does radar show? What does AIS tell us about the other vessel’s intentions? Do we hear a sound signal that hints at maneuvering? Is a radio contact possible to confirm intentions? The moment you start triangulating information, you stand a better chance of spotting a risk early and choosing a safe course.

The toolbox you actually need: a practical mix of ways to sense risk

Here’s the real-world toolkit, kept deliberately simple so you can picture it on deck:

• Visual observation: the old standby. Keep a sharp lookout, scan for lights, shapes, wake, and behavior. Look for unusual traffic patterns, erratic speeds, or a vessel making a maneuver that isn’t aligning with the common traffic rhythm.

• Radar: your night-owl friend. It helps track targets, measure bearing and range, and reveal those sneaky courses that aren’t obvious by sight alone. Radar’s best when visibility is poor, but it isn’t magic—interpret radar returns with care and cross-check them against other cues.

• AIS (Automatic Identification System): a subset of the bigger picture. It gives you vessel identity, course, speed, and sometimes intent. Don’t assume AIS data is perfect—verify, especially if a vessel’s track behavior looks off or if AIS is reporting something that contradicts what you observe.

• Sound signals: the language of intent in fog or busy channels. Short blasts or a prolonged signal can tell you that a vessel is slowing, turning, or changing its plan. Use sound signals as a cue to re-check the math you’re doing with other tools.

• VHF radio and direct communication: sometimes a quick call clears up ambiguity. If you’re unsure what another vessel intends, a polite exchange can prevent a misread and a potential collision.

• Charts and electronic plotting: they keep the broader picture in view. Plot the ships’ courses, calculate relative motion, and compare it with your own vessel’s planned route. Keep a running decision log—what you see, what you think it means, and what you’re going to do about it.

• Other navigational aids as available: GPS fix accuracy, tide and current data, and even observed sea state. Every supportive piece makes your overall judgment sharper.

A simple, repeatable approach to assessing collision risk

To keep the thinking clear when it matters, many crews use a straightforward sequence. You can picture it as a short, steady routine you run in your head and on the bridge:

1. Scan and identify: Look around with eyes and radar. Spot potential risk objects and mark them in your plotting area.

2. Assess relative motion: Are you on a crossing, approaching, or head-on path? How fast are you and the other vessel closing the distance? Is your bearing changing?

3. Check all means: Cross-check what you see visually with what radar shows and what AIS reports. Listen for sound signals. See if VHF calls back up or contradict the data you have.

4. Decide early: If there’s any meaningful risk, plan an action that buys you space. This might mean altering course, changing speed, or both. The goal is to reach a safe margin, not to be the fastest to the next waypoint.

5. Communicate and act: Convey your intentions if needed, and execute the maneuver cleanly. Keep steering and speed changes smooth, predictable, and well-communicated.

6. Reassess and repeat: As you move, keep re-checking. The situation can change fast in busy waters.

This isn’t a rigid checklist so much as a mindset. The best crews treat risk assessment as an ongoing conversation between the ship, its crew, and the environment. The moment one variable shifts—visibility improves or deteriorates, another vessel alters speed—the whole assessment deserves an update.

Common traps to dodge (and what to do about them)

• Over-reliance on one data source: It’s tempting to latch onto AIS if it’s giving clean numbers, or to trust radar without verifying. The cure is cross-check: always compare at least two different means before you commit to a maneuver.

• Misinterpreting data: A target’s course may look steady on radar but can include a subtle, planned turn. Use your plotting tools to test “what if” scenarios and watch how the relative motion changes with small hypothesis shifts.

• Missing unusual traffic patterns: In busy harbors, some vessels don’t follow the usual pace. The fix? Slow down a touch, widen the lookout, and treat anything out of the ordinary as a potential risk until proven otherwise.

• Ignoring environmental limits: Fog, rain, glare, swell—all can warp perception. Allow a larger safety margin when weather or light is compromised.

• complacency with one method in poor conditions: When you lose one signal, you must lean on the others. Stay versatile and ready to adapt.

Why this matters on the water (beyond the test-score vibes)

Collision avoidance isn’t about ticking a box; it’s about real-world safety. Ships don’t operate in a vacuum. They move through weather, currents, traffic, and human decisions. The “all available means” approach respects that complexity. It’s a practical reminder that good seamanship blends science and judgment.

Let me spin a quick, relatable scenario: a large cargo ship and a small fishing boat share a busy channel at dusk. The cargo ship’s AIS shows a steady course, the radar paints a broad picture, and the crew keeps a keen lookout. The fishboat’s lights flicker as a breeze shifts, and the vessel’s wake begins to show a shift in direction that AIS hadn’t flagged quickly enough. The crew on the cargo ship doesn’t wait for a perfect signal. They cross-check, anticipate the turn, and slow down modestly to allow safe passage. The small boat’s operator, meanwhile, notices a large silhouette and uses sound signals to deter any misunderstanding. Within a minute, both are out of each other’s danger zones, and the channel remains open to everyone who respects the rules and keeps the communication lines clear. That’s not cinematic drama—it’s what happens when you use all available means well, and when you stay attentive to the evolving picture.

A few words about practice and readiness (the quiet, steady kind)

People often ask how to stay sharp in this realm. The honest answer is routines. Regular bridge-team drills, tabletop exercises, and real-time practice with your onboard tools keep the instincts alive. You don’t need fancy gear to benefit either. A well-calibrated radar, up-to-date charts, and a habit of confirming AIS data against visual cues can go a long way. And never underestimate the value of a calm, deliberate approach when the waters get crowded or the weather grows capricious.

A quick recap you can carry on your next voyage

• The rule says: use all available means appropriate to the circumstances.

• Don’t lean on a single signal to judge risk. Cross-check visuals, radar, AIS, sound signals, and communications.

• Think in relative motion: identify, assess, decide, act, and re-check.

• Protect the margins: when in doubt, give more space and communicate clearly.

• Keep the crew engaged: good lookout, good communication, and good habits are the trio that make a voyage safer.

If you’re new to this mindset, think of it as a shared language on the water. The more you and your crew speak it fluently, the smoother your passage—even when the seas aren’t perfectly cooperative. And if a moment comes when you’re tempted to cut corners or rely on a single tool, remember the bigger picture: safety isn’t a single “tip” or trick. It’s a practiced way of navigating risk, with every available means playing a part when the situation demands it.

Closing thought: a culture of vigilance that travels with you

The waters won’t pause to let you catch up. They keep moving, your crew changes shifts, and conditions can shift in the time it takes to blink. That’s why the habit of using all available means, promptly and thoughtfully, sticks with you long after the day’s voyage ends. It’s a habit that keeps people and vessels out of harm’s way, and it’s the kind of seamanship that earns trust at sea.

If you’re curious to learn more about how observation, sensors, and communication weave together under COLREGs, you’ll find a lot of practical guidance in the navigation manuals, the latest radar and AIS manuals, and real-world accounts from mariners who’ve seen what happens when plans go right—and what happens when they don’t. The goal isn’t fear or rigidity; it’s confidence—confidence in the moment you need to decide, and in the hours that follow as you responsibly chart your course.