The rules of the road, in plain English

What the COLREGs are

The COLREGs are an international convention, adopted through the International Maritime Organization in 1972 and in force since 1977. Almost every seafaring country has made them law for its ships and its waters, so a container ship, a fishing boat and a dinghy all follow the same rules wherever they meet. They have been amended several times since, for example to cover wing-in-ground craft and to add Part F on checking that countries apply them.

There are 41 rules in six parts, followed by four annexes:

• Part A, General (Rules 1–3): where the rules apply, everyone's responsibility, and definitions.
• Part B, Steering and sailing (Rules 4–19): how to avoid collision: the heart of the rules.
• Part C, Lights and shapes (Rules 20–31): what a vessel shows so others can tell what she is and what she's doing.
• Part D, Sound and light signals (Rules 32–37): whistle signals for manoeuvring, warning and fog.
• Part E, Exemptions (Rule 38) and Part F, Verification of compliance (Rules 39–41).
• Annexes I–IV: the technical details of lights and shapes, extra signals for fishing vessels close together, sound signal equipment, and distress signals.

Part A: who the rules apply to

Rule 1 applies the rules to all vessels on the high seas and all waters connected to them that seagoing vessels can navigate. A country may make special rules for its harbours, rivers and lakes, which is why Canada and the United States have their own additions (see below).

Rule 2, Responsibility, is the one that holds the rest together. Following the rules doesn't excuse you from the consequences of neglecting ordinary good seamanship. And where following a rule exactly would lead straight into danger, you may depart from it as far as needed to avoid immediate danger.

Rule 3, Definitions, sets out the words the other rules depend on. Some that matter most:

• Power-driven vessel: any vessel propelled by machinery. A sailing yacht motoring with her sails up is a power-driven vessel.
• Vessel engaged in fishing: fishing with nets, lines or trawls that restrict her ability to manoeuvre. Trolling lines don't count.
• Not under command: a vessel that, through some exceptional circumstance (an engine or steering failure), can't manoeuvre as the rules require.
• Restricted in her ability to manoeuvre: a vessel whose work limits her movement: dredging, laying cable, replenishing at sea, launching aircraft, minesweeping, or towing in a way that limits her.
• Constrained by her draught: a power-driven vessel severely limited in where she can go because of her depth of water.
• Underway: not at anchor, made fast to the shore, or aground. A vessel can be underway without making way through the water.
• Restricted visibility: any condition, such as fog, mist, falling snow or heavy rain, in which visibility is reduced.

Conduct in any visibility (Rules 4–10)

Rule 5: Look-out

Every vessel keeps a proper look-out at all times, by sight and hearing and by every other means available, radar included. Many collisions start with nobody looking.

Rule 6: Safe speed

Proceed at a speed at which you can take proper and effective action to avoid collision and stop within a suitable distance. What is safe depends on the visibility, how busy the water is, your ship's stopping distance and turning ability, background lights at night, the wind, sea and current, the depth of water and, with radar, its limitations.

Rule 7: Risk of collision

Use every means to decide whether risk of collision exists, and if in doubt, assume it does. The key test: if the compass bearing of an approaching vessel doesn't appreciably change, risk of collision exists. Even a changing bearing can carry risk when approaching a very large vessel, a tow, or a vessel at close range. Don't draw conclusions from scanty information, especially scanty radar information.

Rule 8: Action to avoid collision

Action should be positive, made in ample time, and large enough to be readily apparent to the other vessel by eye or by radar: a series of small alterations is not. An alteration of course alone is often the most effective action if there is room. Check the action works until the other vessel is finally past and clear, and slow down, stop or go astern if you need more time. A vessel required not to impede another must act early to leave room for her safe passage.

Rule 9: Narrow channels

Keep as near the outer limit of the channel on your starboard side as is safe. Vessels under 20 metres, sailing vessels and fishing vessels must not impede vessels that can only navigate safely inside the channel. Don't cross a channel if that impedes such a vessel, and avoid anchoring in one.

Rule 10: Traffic separation schemes

In a scheme, follow the lane in its direction of traffic, keep clear of the separation zone, and join or leave at the ends where possible, otherwise at as small an angle as practicable. Cross a lane on a heading as nearly as practicable at right angles to the direction of traffic. Small vessels, sailing vessels and fishing vessels must not impede vessels following a lane. Rule 10 doesn't take away anyone's duties under the other rules.

Vessels in sight of one another (Rules 11–18)

These rules apply only when the vessels can see each other. Each situation names a give-way vessel, which must keep out of the way, and a stand-on vessel.

Rule 13: Overtaking

A vessel overtaking another keeps out of her way, whatever kind of vessel either is. You are overtaking if you come up on her from more than 22.5° abaft her beam, so that at night you would see only her sternlight. If in doubt, assume you're overtaking. You stay the overtaking vessel until you're finally past and clear: a later change of bearing doesn't make you a crossing vessel.

Rule 14: Head-on

Two power-driven vessels meeting on reciprocal or nearly reciprocal courses each alter course to starboard, so they pass port to port. At night you'd see her masthead lights in line or nearly so, and both her sidelights. If in doubt, assume it is head-on.

Rule 15: Crossing

When two power-driven vessels cross, the one that has the other on her own starboard side keeps out of the way, and if possible avoids crossing ahead of her. Put simply: if you see her red sidelight, she's on your starboard side, and you give way.

Rule 16 and Rule 17: Give-way and stand-on

The give-way vessel takes early and substantial action to keep well clear. The stand-on vessel keeps her course and speed, so the other can predict her. But she may act on her own as soon as it becomes clear the give-way vessel isn't doing what the rules require, and she must act when collision can't be avoided by the give-way vessel alone. If she does act in a crossing situation, she should if possible not turn to port for a vessel on her own port side.

Rule 12: Sailing vessels

Between two sailing vessels: on different tacks, the one with the wind on her port side keeps out of the way. On the same tack, the one to windward keeps out of the way of the one to leeward. If a vessel with the wind on her port side can't tell which tack a vessel to windward is on, she keeps out of the way.

Rule 18: Responsibilities between vessels

Apart from overtaking (Rule 13) and narrow channels and traffic schemes (Rules 9 and 10), a vessel less able to manoeuvre is kept clear of by one more able. From the most privileged down:

1. Not under command, and restricted in her ability to manoeuvre
2. Constrained by her draught (others avoid impeding her)
3. Engaged in fishing
4. Sailing
5. Power-driven

Each keeps out of the way of those above it: a power-driven vessel gives way to a sailing vessel, which gives way to one engaged in fishing. A seaplane on the water keeps well clear of all vessels, and a wing-in-ground craft taking off, landing or flying near the surface keeps well clear of all other vessels.

Restricted visibility (Rule 19)

Rule 19 applies to vessels not in sight of one another in or near an area of restricted visibility. There is no stand-on or give-way vessel: every vessel goes at a safe speed with her engines ready for immediate manoeuvre, and each that detects another by radar alone and finds risk of collision takes avoiding action in ample time. If that action is an alteration of course, so far as possible avoid:

• altering to port for a vessel forward of the beam, other than one you are overtaking;
• altering towards a vessel abeam or abaft the beam.

When you hear another vessel's fog signal apparently forward of your beam, and can't rule out risk of collision, reduce speed to the minimum at which you can keep your course, take all way off if necessary, and navigate with extreme caution until the danger is over. Once the vessels see each other, Rules 11 to 18 apply instead.

Lights and shapes (Part C)

Lights are shown from sunset to sunrise and in restricted visibility; shapes by day. Together they tell another vessel what you are, which way you're heading, and what you're doing.

The basic lights of a power-driven vessel underway (Rule 23)

• Masthead light: white, forward, shining over 225° from right ahead to 22.5° abaft each beam. A vessel of 50 m or more shows a second, higher one further aft.
• Sidelights: green to starboard, red to port, each over 112.5° from right ahead to 22.5° abaft the beam.
• Sternlight: white, over the 135° the masthead light doesn't cover.

Because the masthead and sternlight arcs meet at 22.5° abaft the beam, the lights you see tell you whether you are overtaking (sternlight only), crossing (one sidelight) or meeting head-on (both sidelights).

Common signals of a vessel's state

When making way through the water, the vessels underway in this table also show sidelights and a sternlight (a pilot vessel whenever she's underway), and some also masthead lights. A sailing vessel under sail alone shows sidelights and a sternlight but no masthead light; one also using her engine shows a cone, point down, by day, and is a power-driven vessel under the rules.

Sound and light signals (Part D)

A short blast lasts about one second; a prolonged blast four to six seconds.

Manoeuvring signals, in sight of one another (Rule 34)

In a narrow channel, two prolonged and one short means "I intend to overtake you on your starboard side", two prolonged and two short "on your port side", and the vessel being overtaken agrees with prolonged, short, prolonged, short.

In restricted visibility (Rule 35)

Canadian and US rules

In Canada the COLREGs are made law by the Collision Regulations (C.R.C., c. 1416), which add Canadian modifications, many of them for inland waters such as the Great Lakes, rivers and harbours: for example, in a narrow channel with a current the vessel going down with it has the right of way and proposes how to pass, vessels on the Great Lakes sound whistle signals of intent, and there are special lights for barges and log tows.

In the United States, the Inland Navigation Rules apply inside the demarcation lines, with differences from the international rules: whistle signals that signal intent and are answered by the other vessel, special lights for vessels pushing ahead, and rules for the Great Lakes and Western Rivers. The US Coast Guard publishes both sets of rules together as the amalgamated Navigation Rules.

Colregs Clash has optional question sets on both, so you can practise the rules for the water you sail in.

Ways to remember them

• "Red to red, safe to go ahead": seeing her red sidelight with your own port side towards her, you pass port to port.
• "If to starboard red appear, 'tis your duty to keep clear": her red sidelight on your starboard bow means you are the give-way vessel.
• "Red over red, the captain is dead": not under command.
• "Red over white, fishing at night"; "green over white, trawling tonight"; "white over red, pilot ahead".