COLREGS Guides

Two boats can meet in only three ways: one comes up from behind, they approach nearly bow to bow, or their paths cross. Each has its own rule, and each rule answers the same two questions: who has to keep clear, and what does the other boat do while she does. Knowing which of the three you are in, quickly, is most of the skill.

First, are the vessels in sight of each other?

Rule 11 says Rules 11 through 18 apply only to vessels in sight of one another. If you cannot actually see the other vessel because of fog, darkness or distance, you are not in a head-on, crossing or overtaking situation with her. Rule 19 takes over instead, and it gives nobody the right to stand on (see below).

The three situations side by side

Overtaking: the rule that beats all the others

Overtaking overrides the usual pecking order of Rules 4 through 18: if you are overtaking, you keep clear, whether you are a sailboat or a ship and whether the boat ahead is a fishing vessel or a yacht. The 22.5-degree line matches the arc where a vessel’s sidelights cut off and only her sternlight shows, so the same geometry identifies an overtaking vessel by day and at night. And the duty sticks: Rule 13(d) says a later change in bearing does not turn you into a crossing vessel. You stay responsible for keeping clear until you are finally past and clear.

Head-on: both turn right

The starboard-to-starboard turn works because it needs no conversation. If either boat guessed differently and turned to port, two safe evasive turns would combine into a collision course. That is also why waiting for certainty is dangerous: by the time a borderline head-on situation is unmistakable, the room for an early, obvious turn may be gone. If you are unsure, the rule tells you to assume it is head-on and act on that.

Crossing: find the vessel on your starboard side

If the other vessel is on your starboard side, you are the give-way vessel. A quick check: at night, a red sidelight off your starboard bow means you give way. The rule adds that, if circumstances allow, the give-way vessel should avoid crossing ahead of the other. Turning to pass astern gives you a forgiving margin if you have misjudged her speed; crossing ahead turns any miscalculation into the exact moment your paths meet.

Give-way and stand-on: what each boat actually does

The give-way vessel: act early, act big (Rule 16, Rule 8)

The give-way vessel must take early and substantial action to keep well clear. A turn that is too small or too late does worse than nothing: the stand-on vessel is watching for a change she can recognize, and an ambiguous nudge burns the time she needed. Rule 8 asks for action that is positive, made in ample time, and large enough to be readily apparent to another vessel watching visually or by radar. A succession of small alterations should be avoided. If there is sea room, a substantial alteration of course alone can be the most effective action, provided it does not create another close-quarters situation, and you keep checking until the other vessel is finally past and clear.

The stand-on vessel: hold on, but do not freeze (Rule 17)

1. Keep your course and speed. That is what keeps the give-way vessel’s maneuver from becoming a guess.
2. You may act as soon as it becomes apparent that the give-way vessel is not taking appropriate action.
3. You must act when you are so close that the give-way vessel alone cannot avoid a collision. Take the action that will best help.
4. In a crossing situation, do not turn to port for a vessel on your own port side if you can help it. A port turn swings your bow toward her path instead of away from it.

None of this excuses the give-way vessel. Rule 17(d) says the stand-on vessel’s freedom to act does not relieve the give-way vessel of her duty to keep out of the way.

Sailing vessels and the pecking order

Two sailboats meeting follow their own rule (Rule 12). With the wind on different sides, the boat with the wind on her port side keeps clear. With the wind on the same side, the boat to windward keeps clear. If a boat with the wind on her port side sees another to windward and cannot tell which side the wind is on for her, she keeps clear anyway. For all other combinations, Rule 18 sets out the order: power-driven vessels keep clear of vessels not under command, restricted in their ability to maneuver, engaged in fishing, and sailing vessels; sailing vessels keep clear of the first three; and a vessel fishing keeps clear of the first two. Rule 3 matters here: a sailboat with her engine in gear is a power-driven vessel for steering purposes, even with her sails still up.

That order is conditional. Rules 9, 10 and 13 can override it: a vessel in a narrow channel that can only navigate there (Rule 9), or a boat that is overtaking (Rule 13), changes who owes what.

Judging risk of collision

All three situations depend on the same early warning. Rule 7 says risk of collision exists if the compass bearing of an approaching vessel is not appreciably changing, and that if you are in any doubt the risk is deemed to exist. A steady bearing with closing range is the geometry of a collision, even when the other boat is still far away. The eye is good at noticing a boat that crosses your bow and poor at noticing one that holds a fixed angle while it closes, so check the bearing repeatedly instead of trusting a glance.

The rule also warns against assumptions from scanty information, and the same caution covers electronics: a missing or delayed AIS target does not mean there is no vessel there, since AIS is not required on most recreational boats and can be switched off. Keep a proper lookout by sight and hearing as well (Rule 5).

What changes inland

The three situations work the same on inland waters, with three variations to know (see International vs. Inland Rules):

• Head-on: on the Great Lakes, Western Rivers and specified waters, a power-driven vessel going downbound with a following current has the right-of-way over an upbound vessel, proposes how to pass, and starts the whistle signals (Rule 14(d)).
• Crossing: on those waters, a power-driven vessel crossing a river keeps clear of one going up or down it (Rule 15(b)).
• Signals: a single short blast means “I intend to leave you on my port side” and needs an answering blast before the maneuver (Rule 34).

When you cannot see: fog changes the answer

In restricted visibility, no vessel gets to stand on. Rule 19 says every vessel proceeds at a safe speed with engines ready for immediate maneuver. A vessel that detects another by radar alone must decide whether a close-quarters situation is developing and act in ample time. If she alters course, she should avoid, so far as possible, turning to port for a vessel forward of the beam (other than one being overtaken) and turning toward a vessel abeam or abaft the beam, because turning toward a target you cannot see tends to close the range. If you hear another vessel’s fog signal apparently ahead, slow to the minimum speed at which you can keep steerage, and take all way off if necessary.

Worked examples

Common mistakes

• Making a small, hesitant turn. The other boat cannot see it as a decision. Turn early and by enough to be obvious.
• Standing on for too long. Stand-on does not mean stubborn: you may act once it is clear the give-way vessel is not, and you must act when a collision cannot be avoided by her alone.
• Turning to port in a crossing situation. It usually points you at the other boat’s path.
• Crossing ahead when you could pass astern. Passing astern gives you room if you have misjudged her speed.
• Assuming a sailboat has right of way because sails are up. If her engine is in use she is a power-driven vessel.
• Solving one collision by creating another. Check the whole picture before you turn, and keep checking until the other vessel is past and clear.