Rule 15 explains who must maneuver when vessels cross paths at sea.

Crossing Vessels, Clear Rules: How Rule 15 Keeps the Water Safe

Let’s set the scene. You’re steering your small craft through a busy channel at dawn. A motorboat veers into your line of sight, coming from the opposite direction but not head-on—rather, their path cuts across yours like a skewer through a cucumber. Who should move? Who should stay put? This is the everyday math of the sea, and the answer lives in Rule 15.

What Rule 15 actually covers

Rule 15 is the rule most people remember as “the crossing rule.” In plain terms: when two vessels are on crossing courses and there’s a risk of collision, one vessel has to yield. The other should maintain its course and speed unless the situation changes. The wording might sound formal, but the idea is simple: in a crossing scenario, the vessel that has the other on its starboard side must give way, while the vessel with the other on its port side should keep going.

That “crossing” distinction matters a lot. It’s not about head-on encounters (that’s Rule 14) or overtaking from behind (Rule 13). It’s the case where paths intersect at an angle, and both vessels see the other in a way that could lead to a collision if someone doesn’t act.

The stand-on and give-way roles—what they mean in real life

They sound like characters in a nautical play, but they’re just two sides of a safety partnership.

• Stand-on vessel: This is the vessel that should keep its course and speed. Think of it as the “stay the course” partner. If everything stays as you expect, there’s no need to maneuver. But remember: staying the course isn’t a free pass to reckless speed—if anything about the situation changes or danger appears, the stand-on may still have to take action.

• Give-way vessel: This is the vessel that must take early and substantial action to avoid a collision. If you find the other craft on your starboard side, you’re the give-way vessel. It’s not about harshly steering the other boat away; it’s about making a safe, clear adjustment so everyone has room to pass without drama.

A simple way to picture it: two boats approach each other, one on your starboard side (to your right). If you’re the boat with the other on your starboard side, you give way. If you’re the boat with the other on your port side (to your left), you’re the stand-on vessel, and you keep your current path unless you’re forced to change.

Why Rule 15 matters in real-world waters

Rule 15 isn’t a snazzy rulebook line to memorize; it’s a practical guideline for busy waterways. In harbors, near river mouths, or through crowded channels where ships, ferries, fishing boats, and pleasure craft mingle, the risk of a crossing collision goes up. The rule helps operators anticipate who should move and when. It also clarifies expectations so there’s less hesitation, fewer near-m misses, and a quicker, safer resolution when boats cross paths.

Let me explain with a everyday analogy. Imagine driving through a busy intersection with a walk signal. If you’re turning left and there’s a car coming from the opposite direction on the cross street, who yields? The answer depends on who has the other car on their left or right side—except on the water, the ship version is all about starboard and port. On land, you might rely on traffic signals; at sea, you rely on rules. Rule 15 is the nautical equivalent of making sure everyone knows who should wait and who can go through safely.

How to apply Rule 15 on the water, step by step

• Detect the crossing early. As soon as two vessels appear to intersect paths, start assessing potential risk. The sooner you recognize a crossing situation, the more options you have.

• Determine which vessel is give-way and which is stand-on. Look at the relative bearings. The vessel with the other on their starboard side bears the burden to give way. If you’re unsure, err on the side of caution and act sooner rather than later.

• If you’re the give-way vessel, act early and decisively. You don’t need to perform a grand, sweeping turn. A small, well-judged course change or a reduction in speed is often enough to avert danger. The key is clarity—make your intention obvious to the other vessel with a measured maneuver.

• If you’re the stand-on vessel, hold your course and speed unless visibility or circumstances demand otherwise. Don’t race to beat the other boat; act only if you must to maintain safety. If the give-way action isn’t enough, you should be prepared to adjust as well.

• If the situation remains unsafe, both vessels should take action to reach a safe outcome. Rule 17 and other rules can come into play when there’s confusion or multiple threats. The bottom line: safety comes first, and decisive action beats hesitation.

• Keep a plan, not a panic. On the water, a calm, deliberate approach works far better than frantic last-minute moves. Think of it like driving in rain: slow, steady, and predictable wins the day.

Practical tips you can put to use

• Look to the starboard and port early. A quick glance at the relative position of other vessels can tell you who has priority. Don’t rely on luck—build a habit of checking.

• Use speed as a tool, not a weapon. Slowing down is often the simplest, safest way to create space without creating new risks for everyone around you.

• Maintain a proper lookout. In busy channels, there are always more boats around than you can count. A vigilant watch keeps you from missing a crossing you’d regret.

• Communicate when the situation is unclear. A quick VHF call or a short blast on the horn can confirm your intentions and prevent misinterpretations. Clear communication reduces the chance of a collision.

• Don’t assume others will yield. Even if you think you’ve identified the stand-on or give-way vessel, conditions change. Be ready to adapt.

• Consider the environment. Wind, current, visibility, and traffic density all influence how you apply Rule 15. In rough conditions, give yourself more margin and slower speeds.

Real-world tangents that help you see the bigger picture

• Lights and shapes: At night or in reduced visibility, the same crossing logic applies, but you’ll also be paying attention to navigation lights and shapes to confirm which vessel is moving in which direction. A proper lookout, plus correct use of lights, helps everyone see who should act.

• AIS and radio checks: Modern boats bring extra clarity. If you’re within range of an AIS-equipped vessel, you can often confirm another craft’s course and speed, which makes Rule 15 decisions much less ambiguous. A quick radio check can clear up anything that’s unclear.

• Weather and traffic density: In busy channels, even small misreads can escalate quickly. It’s best to slow down a notch and give yourself more space when the harbor starts to feel crowded or the seas pick up.

• Training and mindset: Short, realistic drills can make Rule 15 second nature. Practicing how you respond to a crossing in calm conditions builds confidence for when conditions are less forgiving.

The big picture: Rule 15, safety, and everyday navigation

Rule 15 isn’t a dry rule to debate in a classroom; it’s a practical guide that helps boats of all sizes share the water safely. When two vessels cross, the rule provides a clear path to action, striking a balance between predictability and flexibility. You don’t always know what the other person will do, but you can control your own behavior. That’s the essence of safe navigation.

If you’re ever unsure in a crossing situation, think of Rule 15 as your quick reality check: who has the other on their starboard side? If you’re the one with the other on your starboard side, you’re the give-way vessel. If the other vessel has you on their starboard, they’re the give-way vessel and you’re the stand-on. The goal is simple: prevent collisions by making deliberate, well-communicated moves early.

A quick mental exercise to lock it in

Picture two boats approaching a harbor entrance from slightly different angles. Boat A is coming from the east, Boat B from the south. If Boat A sees Boat B on its starboard side, Boat A must give way. Boat B, with Boat A on its port side, should keep its course unless it becomes necessary to alter. In this moment, both boats should stay calm, monitor their bearings, and adjust as needed to pass at a safe distance.

The sea can be a forgiving teacher, but it doesn’t forgive haste. Rule 15 brings a calm, methodical approach to crossing situations that, if mishandled, could lead to harm. It’s a rule built on the basics of seamanship—look out, assess, decide, act.

To wrap it up

Crossing situations are a daily reality on the water. Rule 15 clarifies who yields and who holds steady when two vessels’ paths intersect. The stand-on vessel keeps its course and speed, while the give-way vessel takes early, decisive action to avoid a collision. In crowded channels and busy waterways, this simple framework saves time, reduces risk, and keeps everyone safer.

So next time you’re piloting through a busy stretch, take a moment to map out the crossing in your head. Ask yourself: Is there a vessel on my starboard side? Am I the give-way or the stand-on? If action is required, act early and clearly. If not, maintain a steady course and keep a watchful eye. The water offers plenty of surprises, but with Rule 15 in your toolbox, you’ll navigate them with a confident, steady hand.