How the rules are organised
Part B of the COLREGS has three sections. Rules 4 to 10 apply in any visibility. Rules 11 to 18 apply only to vessels in sight of one another. Rule 19 covers vessels not in sight of one another in restricted visibility, where there's no stand-on vessel at all: see Rule 19 explained.
Lookout · Rule 5
Keep a proper lookout at all times, by sight and hearing and by every other available means, such as radar and AIS. Most collisions involve a failure here.
Safe speed · Rule 6
Always go at a speed that lets you take proper action to avoid a collision and stop in a suitable distance. Visibility, traffic, your manoeuvrability, background lights at night, wind, sea and current, and the depth all count.
Risk of collision · Rule 7
Use every available means to decide whether risk exists, and if in doubt, assume it does. A steady compass bearing with a closing range means risk. Risk can still exist with a changing bearing when approaching a very large vessel, a tow, or anything at close range.
Action to avoid collision · Rule 8
Any action should be positive, made in ample time, and large enough to be readily apparent to the other vessel: no series of small alterations. Slowing down or stopping is allowed. Then check the action is working until the other vessel is past and clear.
Sailing vessels · Rule 12
With the wind on different sides, the vessel with the wind on her port side keeps out of the way. With the wind on the same side, the windward vessel keeps clear. If you're on port tack and can't tell which side the other has the wind, keep clear. The windward side is opposite the one the mainsail is carried on.
Overtaking · Rule 13
Any vessel overtaking another keeps out of the way, whatever else the rules say, until she is finally past and clear. You're overtaking when coming up from more than 22.5 degrees abaft the other's beam. If in doubt, assume you are.
Head-on · Rule 14
Two power-driven vessels meeting on reciprocal or nearly reciprocal courses both alter to starboard, passing port to port. At night you'd see her masthead lights in line or nearly so, and both sidelights. If in doubt, assume it's head-on.
Crossing · Rule 15
When two power-driven vessels are crossing, the one with the other on her own starboard side keeps out of the way and, if possible, avoids crossing ahead of her.
Give-way vessel · Rule 16
Take early and substantial action to keep well clear.
Stand-on vessel · Rule 17
Keep your course and speed. You may take action yourself once it's apparent the give-way vessel isn't acting appropriately, and you must when a collision can't be avoided by her action alone. In a crossing situation, a power-driven stand-on vessel should not alter to port for a vessel on her own port side. Standing on never removes the duty to avoid a collision.
Who keeps clear of whom (Rule 18)
Except where the narrow channel, traffic separation and overtaking rules say otherwise:
- A power-driven vessel underway keeps clear of a vessel not under command, restricted in her ability to manoeuvre, engaged in fishing, or sailing.
- A sailing vessel keeps clear of a vessel not under command, restricted in her ability to manoeuvre, or engaged in fishing.
- A vessel engaged in fishing keeps clear, so far as possible, of a vessel not under command or restricted in her ability to manoeuvre.
- Any vessel other than one not under command or restricted in her ability to manoeuvre should, if possible, avoid impeding a vessel constrained by her draught.
Narrow channels and traffic separation schemes
In a narrow channel, keep to the starboard side, and if you're under 20m or sailing, don't impede a vessel that can only navigate within it (Rule 9). In a traffic separation scheme, cross on a heading as close as practicable to a right angle to the traffic flow, and under 20m or sailing, don't impede power-driven vessels following a lane (Rule 10). Both override Rule 18's pecking order, so a yacht under sail doesn't get right of way over a ship in a channel.