The International Regulations for Preventing Collisions at Sea are published by the International Maritime Organization (IMO), and set out the "rules of the road" to be followed by ships and other vessels at sea.

In the UK they are still often referred to as the "Collision Regulations" (or ColRegs), their former name. In the USA a slightly different version is in use, called the "Navigation Rules" (NavRules); these contain rules for navigation on US inland waters as well as at sea.

The ColRegs form an integral part of the Racing Rules of Sailing, which govern the conduct of yacht and dinghy racing.

The Convention on International Regulations for Preventing Collisons at Sea was adopted by the IMO member countries on 20 October 1972 and the regulations were brought into force on 15 July 1977. The regulations have subsequently been revised in 1981, 1987, 1989, 1993 and 2001. The 1972 regulations replaced the Collision Regulations first adopted in 1960. The regulations are made of five parts A) General, B) Steering and Sailing, C) Lights and Shapes, D) Sound and light signals and E) Exemptions.

Summary of the rules

The rules are specified in great detail in the regulations and the serious student is encouraged to seek the definitive document. However the rules are summarized below.

Part A - General

1. Application

The rules apply to all vessels in all tidal waters.

2. Responsibility

Owners, masters, and crew are all responsible for following the rules.

3. General Definitions

Defines vessel, sailing vessel, power-driven vessel and a number of other terms used in subsequent rules.

Part B - Steering and sailing

4. Application

The rules apply in any visibility.

5. Look-out

Vessels must keep a proper look-out by all available means.

6. Safe speed

Vessels must proceed at a safe speed for the prevailing conditions.

7. Risk of Collision

Vessels must use all means to determine the risk of a collision.

8. Action to avoid collision

Actions taken to avoid collision should be:

• positive
• obvious
• made in good time

9. Narrow channels

• A vessel proceeding along a narrow channel must keep to starboard.
• Small vessels or sailing vessels must not impede (larger) vessels which can navigate only within a narrow channel.
• Ships must not cross a channel if to do so would impede another vessel which can navigate only within that channel.

10. Traffic separation schemes

Ships must cross traffic lanes "as nearly as practicable" at right angles to the direction of traffic. This reduces confusion and enables that vessel to cross the lane as quickly as possible.

11.

The following rules 11-18 applies to vessels in sight of one another.

12 Sailing vessels

Two sailing vessels approaching one another must give-way as follows:

• Port gives way to Starboard. When each has the wind on a different side, the vessel which has the wind to port must give way;
• Windward gives way to leeward. When both have the wind on the same side, the vessel which is windward must give way to the vessel which is leeward;
• Unsure port gives way. If a vessel, with the wind on the port side, sees a vessel to windward and cannot determine whether the other vessel has the wind on the port or the starboard side, they must give way.

13. Overtaking

The overtaking vessel must keep well clear of the vessel being overtaken.

14. Head-on situations

When two power-driven vessels are meeting head-on both must alter course to starboard so that they pass on the port side of the other.

15. Crossing situations

When two power-driven vessels are crossing, the vessel which has the other on the starboard side must give way.

16. The give-way vessel

The give-way vessel must take early and substantial action to keep well clear.

17 The stand-on vessel

The stand-on vessel may take action to avoid collision if it becomes clear that the give-way vessel is not taking appropriate action.

18. Responsibilities Between Vessels

Except in narrow channels, traffic schemes, and when overtaking (i.e. rules 9, 10, and 13)

• A power-driven vessel must keep give way to:
  • a vessel not under command;
  • a vessel restricted in ability to maneuver;
  • a vessel engaged in fishing;
  • a sailing vessel.
• A sailing vessel must give way to:
  • a vessel not under command;
  • a vessel restricted in ability to maneuver;
  • a vessel engaged in fishing.

19. Restricted visibility

A vessel detecting by radar another vessel should determine if there is risk of collision and if so take avoiding action. A vessel hearing the fog signal of another vessel should reduce speed to a minimum.

Part C - Lights and shapes

20. Application

Rules concerning lights apply from sunset to sunrise.

21. Definitions

Gives definitions for various types of light. 'Sidelights' means a green light on the starboard side and a red light on the port side.

22. Visibility of lights

Lights must be visible as follows;

• In vessels of 50 metres or more in length:
  • a masthead light, 6 miles;
  • a sidelight, 3 miles;
  • a towing light, 3 miles;
  • a white, red, green or yellow all-around light, 3 miles.
• In vessels between 12-50 meters in length;
  • a masthead light, 5 miles;
  • a sidelight, 2 miles;
  • a sternlight, 2 miles;
  • a white, red, green or yellow all-round light, 2 miles.
• In vessels less than 12 meters in length:
  • a masthead light, 2 miles;
  • a sidelight, 1 mile;
  • a towing light, 2 miles;
  • a white, red, green or yellow all-around light, 2 miles.

23. Lights displayed by power-driven vessels underway

A power-driven vessel underway must display:

• a masthead light forward;
• If over 50m length a second masthead light aft and higher than the forward one;
• sidelights;
• a sternlight.
• A hovercraft must also display an all-round flashing yellow light.
• A power-driven vessel of less than 12 meters may display only an all-round white light and sidelights.
• A power-driven vessel of less than 7 meters whose maximum speed does not exceed 7 knots may display only an all-round white light.

24. Lights for vessels towing and pushing

25. Lights for sailing and rowing vessels

26. Lights for fishing vessels

27. Lights for vessels not under command or restricted in their ability to manoeuvre

28. Lights for vessels constrained by their draught

29. Lights for pilot vessels

30. Lights for vessels anchored and aground

• A vessel at anchor must display an all-round white light or one ball and at the stern and at a lower level than the first light, an all-round white light

31. Lights for seaplanes

Part D - Sound and light signals

32. Definitions of whistle, short blast, and prolonged blast

33. Equipment

Vessels 12 metres or more in length should carry a whistle and a bell and vessels 100 metres or more in length should carry in addition a gong.

34. Manoeuvring and warning signals, using whistle or lights

35. Sound signals to be used in restricted visibility

36. Signals to be used to attract attention

37. Distress signals

References

• IMO page on the Regulations (http://www.imo.org/Conventions/mainframe.asp?topic_id=257&doc_id=649)