COLREGs: An essential guide

29th June 2021 Elena Manighetti

COLREGs: An essential guide

If you’re new to boating, you won’t be familiar with COLREGs, which are navigation rules. No need to worry. These rules are fairly simple; you just need to give yourself time to memorise them carefully. 

In this article, we look at what COLREGs are, why they are so important and who needs to comply with them. It will be a useful refresher to take with you on your first boating trips of the season.

Deckee ambassador Scratchie in Port Stephens. Photo: Owenphoto

What’s the meaning of COLREGs?

The acronym COLREGs stands for The International Regulations for Preventing Collisions at Sea 1972. They are a set of rules valid throughout the world. If followed, they ensure no collisions happen at sea.

Why are COLREGs important?

COLREGs exist to avoid collisions at sea, which can often be fatal. The rules are crucial because they apply internationally, so all crew and captains need to abide by them anywhere in the world. This way, there are no potential misunderstandings about who needs to give way.

How many rules are in the COLREGs convention?

There are 72 COLREGs regulations. These were developed by the Inter-Governmental Maritime Consultative Organization (IMCO) in 1972. The association was later renamed the International Maritime Organization (IMO) in 1982.

The convention is divided into five parts: 

  1. part A: general 

  2. part B: steering and sailing rules 

  3. part C: lights and shapes 

  4. part D: sound and light signals 

  5. part E: exemptions.

Who is responsible to comply with COLREGs?

Anyone navigating waters outside of the COLREGs Demarcation Lines. These separate the high seas from harbours, rivers, and inland waterways. Inside the Demarcation Lines, sailors need to comply with the Inland and International Rules. 

COLREGs don’t interfere in any way with local law. Every country can set their own station or signal lights, shapes, and whistle signals for warships, vessel convoys, and fishing vessels. 

So on top of the COLREGs, you will need to learn the Inland Navigational Rules for the country you’re sailing in. 


The most important rules in the COLREGs

When sailing the high seas, you need to be familiar with all COLREGs, so you can keep yourself and other people safe. However, we have collected the most important rules to help you refresh your memory on your first few sails of the year.

Rule 5: Look-out

According to rule 5, there should be a watch keeper on deck at all times. They should be using all tools at their disposal to keep vigilant. This means using their eyes, ears, binoculars, VHF, AIS, and radar (if fitted). 

Tips to keep a good watch

Listen to VHF channel 16 and keep an ear out for any sound signals, such as a fog horn. Scan the horizon frequently, using the binoculars as necessary, and keep an eye on your AIS and radar screens. 

Rule 7: Risk of collision

Rule 7 is strictly related to rule 5. The watch keeper should be able to determine the risk of collision when they spot a target. 

Tips to determine the risk of collision

If you see a light or vessel on the horizon, take bearings with the hand-held compass to figure out in which direction they’re moving and how fast. Compare their likely course with yours. There should be a reasonable change (more than 2-3 degrees) in the compass bearing of the vessel. Otherwise, you’re at risk of collision.

Scanty information  

The regulation also warns against incomplete (scanty) information. There are three common mistakes that can lead you to make an inaccurate risk calculation:

  • not taking a compass bearing

  • relying on radar information only 

  • not monitoring the situation to confirm if the vessel is passing ahead or astern of you.

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Rule 6: Safe speed

All vessels should proceed at a safe speed, based on the situation. The safety of a vessel’s speed is based on: 

  • how soon the vessel can spot a target 

  • how fast they can take avoiding action.

These two factors are affected by:

  • weather conditions

  • draught - a smaller draught to depth radio makes a boat less maneuverable

  • state of visibility 

  • traffic density 

  • manoeuvrability of the vessel

  • background lights - these can confuse a watch keeper.

So a very manoeuvrable vessel can sail at a faster speed than a less manoeuvrable one. 

Top tip

Make sure you adjust your speed based on the situation. In heavy fog or dense traffic, slow down. Take your time to assess the risk of collision with each target.

Rule 15: Crossing situation

This regulation explains what to do in a crossing situation. It’s important to remember that rule 15 applies to two power-driven vessels only. Both boats need to be travelling under engine; otherwise a sailing vessel would have priority over a powerboat.

When you’re on a boat under engine, if you see a power-driven vessel on your starboard side, you need to give them way and avoid crossing ahead of them, if possible. You can achieve this by slowing down or altering course.

You should always alter course to starboard, if you can, so you can pass behind the stand-on vessel. If there are navigational hazards or vessels on your starboard side, you can alter to port, but you should do this early on, to clearly show your intentions. 

Rule 14: Head-on situation

When two power-driven vessels are meeting on the same course, each vessel should alter their course to starboard and pass the other vessel on the port side. 

Tips to recognise a head-on situation

You’re in a head on situation if:

  • you see the other vessel ahead or nearly ahead

  • or you see the masthead lights of the vessel in a line, or nearly in a line

  • or you see both sidelights in a line, or nearly in a line.

If you’re in doubt, alter course.

sail Port Stephens. rodd owen

Rule 12: Sailing vessels

When two approaching sailing boats are at risk of collision, the rules change slightly. Below are the possible situations you’ll encounter and how to handle them.

Wind on different sides

When the two yachts have the wind on different sides, the one with the wind on the port side will give way to the other.

Wind on the same side

When both sailboats have the wind on the same side, the vessel to windward needs to keep out of the way.

Unable to determine tack

When a vessel with the wind on the port side sees a yacht to windward and can’t determine on which tack they are on, they will give way to the other boat.

Rule 16: Action by give-way vessel

Every vessel that needs to give way, based on the COLREGs convention, will need to take avoiding action as early as possible. The course alteration needs to be meaningful, so it’s clearly spotted by the other vessel.

Rule 17: Action by stand-on vessel

In a collision situation, the stand-on vessel should maintain course and speed. If, however, the give-way vessel is not taking avoiding action, the stand-on vessel can prevent a collision any way they can.

Boating at sunset. Photo: Rodd Owen


We collected the most popular questions and answers about COLREGs below. 

What are the lights prescribed by the COLREGs?

All vessels should have installed:

  • a masthead light 

  • a white, red, green or yellow, all-round light

  • a side light

  • a sternlight

  • a towing light.

The visibility requirements for each light change, based on the length of the vessel.

Submerged vessels or objects being towed, need to display a white all-round light, visible from at least 3 miles away.

What is Rule 3 of the International Regulations for Preventing Collisions at Sea 1972?

Rule 3 is about the definitions of words used in the convention. This ensures everyone understands the jargon used in the rules. For example, rule 3 defines a vessel ‘underway’ as a watercraft that is not at anchor, or tied to the shore, or aground.

What is Rule 22 of the collision regulations?

Rule 22 of COLREGs is about navigation lights. It describes the kind of lights vessels should display, as well as the minimum range of visibility for each light. For example, the masthead light of a vessel over 50m long should be visible from 6 miles away.

*Knowing the COLREGs is essential to prevent collisions at sea. Make sure you memorise all the rules before you set sail, in order to stay safe. Don’t forget to learn the Inland Navigational Rules of the country you’re in, so you won’t get confused when you’re near the shore.

If you’d like to learn all COLREGs in detail, which we strongly recommend, head over to this free online resource: Master COLREGs.

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