Overtaking, Head-on and Crossing Situations

The three situations at a glance

In short: Read Risk of Collision and Action to Avoid Collision first. Once risk of collision exists, you must name the situation: overtaking (Rule 13), head-on (Rule 14) or crossing (Rule 15). The name tells you who keeps out of the way and which way to turn.

• These rules sit in Part B Section II (Rules 11–18). Rule 11: they apply only to vessels in sight of one another.
• A radar-only contact in fog is not overtaking, head-on or crossing: Rule 19 applies instead (see the radar section below).
• Work in this order on the bridge: is there risk of collision? → is she in sight? → which situation? → do Rule 18 or Rules 9/10 change who gives way? → act (Rule 16 or Rule 17).

Rule 13 — overtaking

In short: If you come up on another vessel from more than 22.5° abaft her beam, you are overtaking and you keep out of the way, whatever kind of vessel you are. If in doubt, you are overtaking.

• Rule 13(a) — any vessel overtaking any other keeps out of the way of the vessel being overtaken. This applies notwithstanding Rules 4–18 (Part B Sections I and II).
• So Rule 13 beats Rule 18: a sailing vessel or a vessel engaged in fishing that overtakes a power-driven vessel must keep clear of her. Rule 18 itself opens with “except where Rules 9, 10 and 13 otherwise require”.
• Rule 13(b) — you are overtaking when you come up with her from a direction more than 22.5° abaft her beam.
• Rule 13(c) — if in doubt, assume you are overtaking and act accordingly.
• Rule 13(d) — a later change of bearing does not turn you into a crossing vessel and does not release you. You keep clear until finally past and clear.

How to know you are overtaking

• At night: you can see only her sternlight, neither sidelight (Rule 13(b)).
• Why 22.5°: each sidelight shows over 112.5°, from right ahead to 22.5° abaft the beam on its side. The sternlight covers the remaining 135° astern (67.5° each side of right astern). The masthead light covers 225°, to the same 22.5° abaft the beam (COLREG Rule 21).
• By day: judge her aspect — are you more than 22.5° abaft her beam? Radar and AIS help, but a fine call near the line is a doubt, so Rule 13(c) makes you the overtaking vessel.
• On the bridge: you are a fast yacht coming up on a slow coaster from her port quarter. Her bearing slowly draws forward as you pass. You are still the overtaking vessel (Rule 13(d)) — do not start treating her as a crossing ship on your port side.

Must the vessel being overtaken keep her course and speed?

• A favourite oral question. Rule 13 itself says nothing about the vessel being overtaken: it puts the whole duty on the overtaking vessel.
• Her duty comes from Rule 17(a)(i): where one of two vessels must keep out of the way, the other keeps her course and speed. So yes — she is the stand-on vessel.
• Rule 17 then lets her act: she may act once it is clear the overtaking vessel is not doing enough (17(a)(ii)) and must act when collision cannot be avoided by the other alone (17(b)). Remember SHALL – MAY – SHALL.
• In a narrow channel, overtaking may need the overtaken vessel’s help (Rule 9(e)), agreed with the sound signals of Rule 34(c): two prolonged + one short = “I intend to overtake you on your starboard side”; two prolonged + two short = “on your port side”; agreement = prolonged, short, prolonged, short; in doubt = at least five short and rapid blasts (Rule 34(d)). See Narrow Channels and Traffic Separation Schemes.

Rule 14 — head-on situation

In short: Two power-driven vessels meeting on reciprocal or nearly reciprocal courses with risk of collision: both alter course to starboard and pass port to port. Nobody stands on.

• Rule 14(a) — each vessel alters course to starboard so that each passes on the port side of the other.
• Rule 14(b) — the situation exists when you see the other vessel ahead or nearly ahead: by night her masthead lights in line or nearly in line and/or both sidelights; by day the matching aspect.
• Rule 14(c) — if in doubt, assume it is head-on and act.
• It applies only between two power-driven vessels. A sailing vessel or a vessel engaged in fishing met head-on falls under Rule 12 or Rule 18.
• Make the turn early and large (Rule 8(b)) so the other ship sees it by eye or radar. In sight of each other, sound one short blast = “I am altering my course to starboard” (Rule 34(a)).
• On the bridge: at night you see a ship right ahead, both masthead lights in line, red and green. Alter boldly to starboard, sound one short blast, keep plotting until past and clear.

The one-sidelight trap

• A vessel ahead or nearly ahead showing only one sidelight is not head-on. If risk of collision exists, it is a crossing situation (Rule 15).
• Her red light means you are on her port side; her green light means you are on her starboard side.
• Red on your starboard bow, bearing steady → she has you on her port side, so you have her on your starboard side: you give way. Memory aid: “If to starboard red appear, ’tis your duty to keep clear.”
• Green on your port bow, bearing steady → you have her on your port side: she gives way, you stand on (Rule 17).
• Examiners use this from past orals: they show one sidelight fine on the bow and wait for “head-on, alter to starboard”. Name the right rule first.

Rule 15 — crossing situation

In short: Two power-driven vessels crossing with risk of collision: the one that has the other on her own starboard side keeps out of the way and, if possible, does not cross ahead. The other stands on.

• Rule 15 — the give-way vessel keeps out of the way and, if the circumstances allow, avoids crossing ahead of the other. In practice: alter to starboard and pass astern, or slow down / stop.
• Rule 16 — the give-way vessel takes early and substantial action to keep well clear.
• Rule 17 — the stand-on vessel: shall keep course and speed (17(a)(i)); may act alone once the give-way vessel is clearly not acting (17(a)(ii)); shall act when collision cannot be avoided by the give-way vessel alone (17(b)). SHALL – MAY – SHALL.
• Rule 17(c) — a power-driven stand-on vessel acting under 17(a)(ii) does not alter to port for a vessel on her own port side, if the circumstances allow. A turn to port can meet the give-way vessel’s late turn to starboard.
• Rule 17(d) — the give-way vessel is never released by what the stand-on vessel does.

When Rule 18 decides: turning to port

• Rule 15 is only for two power-driven vessels. If the crossing vessel is sailing, engaged in fishing, RAM or NUC, Rule 18 decides: as a power-driven vessel you keep clear of her even if she is on your port side.
• With such a vessel on your port side, an alteration to port to pass astern of her can be the correct action. Rule 15’s “vessel on your starboard side” logic does not apply, and you are the give-way vessel, so Rule 17(c) does not stop you.
• Tug with tow: check her signals. If she shows RAM (ball–diamond–ball; red–white–red all-round lights), her tow severely restricts her ability to deviate from course: she ranks above you under Rule 18 and you keep clear. If she is only a power-driven vessel towing (no RAM signals), Rule 15 applies as normal: on your port side, she gives way to you.
• Rule 13 still beats Rule 18: a fishing vessel or sailing vessel that is overtaking you keeps clear of you.

Identifying the situation on radar and AIS

In short: Use the radar and AIS to name the situation and measure the risk: work from identify → risk? → decide → act → check → resume. But a contact seen only on radar is a Rule 19 case, not Rules 13–15.

• Target tracking (TT) gives range, bearing, course and speed. It is the primary source: independent detection, automatic, many targets at once, reliable.
• AIS gives type, position, heading, course, speed, navigational status and destination. It relies on GNSS on the other ship, so it can be wrong.
• Association of TT and AIS gives the best picture with less duplicate information. A manual plot or systematic observation is slower, handles fewer targets and is less accurate.
• A plot gives the target’s aspect, course and speed: these tell you whether she is being overtaken, meeting you head-on or crossing — and from which side.
• Measure the risk with CPA and TCPA against your limits: both at or under the limits = dangerous, act now. Modern radars flag dangerous targets in red automatically.
• Situations change: keep identifying with an uninterrupted look-out, information from the other ships and cooperation in the bridge team.

Not in sight: Rule 19, not Rules 13–15

• Rules 13–15 need vessels in sight of one another (Rule 11). In restricted visibility, with a radar-only contact, there is no stand-on and no give-way vessel: every vessel acts under Rule 19.
• Rule 19(d): if a close-quarters situation is developing, avoid, as far as possible, (i) an alteration to port for a vessel forward of the beam, other than one being overtaken, and (ii) an alteration towards a vessel abeam or abaft the beam.
• On the bridge: in fog you plot a target crossing from your starboard bow. Do not say “I am give-way under Rule 15”: say “Rule 19 — I take avoiding action in ample time, alter to starboard or reduce speed”.