The official title, commonly shortened to Colregs, of the internationally agreed rules by which ships at sea keep clear of each other. The first international conference to consider such rules was held in Washington in 1889 and the regulations agreed were brought into force in several countries, including Britain and the USA, in 1897. A further international conference was held in Brussels in 1910 and the regulations then agreed remained in force until 1954 when revisions made at the International Convention for the Safety of Life at Sea (SOLAS) conference in 1948 came into force. In 1960 the intergovernmental maritime consultative organization, now the International Maritime Organization (IMO), an agency of the United Nations, convened a SOLAS conference which agreed certain alterations to the rules. Today the IMO has the responsibility, exercised through its maritime safety committee, for altering the regulations.
There are 38 rules which are divided into four parts, a to d, which cover application, responsibility, and general definitions; steering and sailing rules to keep vessels apart when they are approaching each other or are in restricted visibility; lights and shapes to be carried by vessels at night or by day by which they can be recognized; and sound and light signals. There are also four annexes covering the positioning and technical details of lights and shapes; additional signals for fishing vessels fishing in close proximity; technical details of sound signal appliances; and distress signals. One of the most important new rules, which applies to yachtsmen and fishermen as well as to merchant shipping, is Rule 10 which deals with traffic separation schemes.
Of the definitions laid down, the most important are those which define a power-driven and a sailing vessel. A vessel with any form of mechanical propulsion, including oars, counts as a power-driven vessel; a sailing vessel is one propelled by sails only; a yacht with her sails spread which is also using her auxiliary engine is a power-driven vessel.
Under the regulations the lights a vessel is obliged to carry at night serve two purposes. Its navigation lights, or steaming lights as they are also called, are so designed and placed that any other ship sighting them can tell reasonably accurately the course of the vessel carrying them. The regulations also lay down other lights which must be carried by certain vessels to indicate their type and actual employment. For example, a fishing vessel engaged in trawling must show an all-round green light above an all-round white light, in addition to its navigation lights.
During daylight signals are displayed by hoisting cones or black balls, and in restricted visibility, day or night, fog signals are used to indicate a vessel's movements and sometimes its employment. Below are extracts from the regulations about the more commonplace sound and visual signals, including distress signals, but if in doubt mariners should refer to the regulations themselves as there are exemptions and qualifications to some of the rules, and some do not apply to small craft.1. Blasts from a ship's whistle or foghorn can be used by it to indicate a change of course. One short blast indicates that the vessel is altering its course to starboard; two short blasts indicate that it is altering course to port; and three short blasts indicate that it is going astern.2. When one vessel is in sight of another in a narrow channel or fairway the overtaking vessel should indicate its intentions by two prolonged blasts and one short one, indicating that it is intending to overtake the other vessel on that vessel's starboard side, and by two prolonged blasts and two short blasts when it intends overtaking the other vessel on that vessel's port side. The vessel being overtaken should indicate its agreement by one prolonged and one short blast, repeated once immediately.3. If one vessel, for any reason, does not understand the intentions or actions of another vessel which is approaching it, or is unsure that sufficient action is being taken to avoid a collision, then it shall immediately indicate such doubt by giving at least five short and rapid blasts.4. When a vessel is approaching a bend or an area of a channel where other vessels may be obscured it should sound one prolonged blast. This signal should be answered by any vessel hearing it by a similar blast.5. A vessel not under command during the day displays two balls or similar shapes in a vertical line where they can best be seen. At night it displays two all-round red lights in a vertical line where they can best be seen.6. A vessel restricted in its ability to manoeuvre (except one engaged in clearing mines) shall display a ball shape, a diamond shape, and another ball shape in a vertical line where they can best be seen.7. A vessel at anchor shall display in its fore part one ball.8. A vessel aground shall display three balls in a vertical line.9. A vessel towing another vessel, or vessels, in excess of 200 metres (656 ft) shall display a diamond shape where it can best be seen.The most important group of rules are the steering and sailing ones, which lay down the procedures to be followed when ships approach each other and there is a danger of collision. Where this happens, the rules lay down which ship is to give way to the other. In a broad sense, vessels keep to the right when at sea. If, for example, two ships are approaching each other head on, both must alter course to starboard (to the right) so that they pass each other port side to port side. Where a vessel is on the starboard hand of another, and steering a course which may result in a collision, it has the right of way and should maintain its course and speed, the other vessel giving way to it. Where a vessel is on the port hand of another, and its course, if it maintains it, may result in a collision, it is the giving way vessel and must alter course to avoid the other. These basic tenets are enshrined in the well-known doggerel written by Thomas Gray, head of the British Board of Trade's marine department, towards the end of the 19th century:When both side-lights you see ahead,Port your helm and show your red.Green to green, and red to red,Perfect safety go ahead.When on your starboard red appear,It is your duty to keep clear,To act as judgment says is proper,To port or starboard, back or stop her.But when upon your port is seen,A steamer's starboard light of green,There's not much for you to do,For green to port keeps clear of you.Both in safety and in doubt,Always keep a good look-out.In danger with no room to turn,Ease her, stop her, go astern.However, any ship overtaking another, i.e. approaching at any angle from two points abaft the beam on either side, must keep clear. Also, generally speaking, all power-driven vessels must keep clear of all vessels under sail, although there are always circumstances (e.g. a sailing vessel approaching a very large bulk carrier in narrow waters) where the sailing vessel will keep clear. The only rule to which this does not apply is the overtaking rule; a sailing vessel overtaking a power-driven vessel must keep clear of it. When a vessel has the duty of giving way to another under the rules, it normally does so by altering course to pass astern of the other, and should make a clear and significant alteration of course in plenty of time to indicate to the other vessel that it is taking the appropriate action.