COLREGS

The COLREGs are the international traffic rules of the sea. Adopted by the IMO in 1972 and in force since 1977, they apply to all vessels on the high seas and on waters connected to them, and every watchkeeping officer must know them thoroughly because they are examined in detail for a Certificate of Competency. Their single purpose is to prevent collisions by making the behaviour of ships predictable to one another.

The rules are grouped into parts. The steering and sailing rules define how vessels must act in any condition of visibility and, critically, in sight of one another: which vessel is the 'give-way' vessel and which is the 'stand-on' vessel in crossing, overtaking and head-on situations, and how each must manoeuvre. A separate set of rules governs conduct in restricted visibility, when vessels navigate by radar and sound signals rather than by sight. Further rules establish a hierarchy of responsibility between different types of vessel — for example, a power-driven vessel generally gives way to one not under command, restricted in her ability to manoeuvre, or engaged in fishing.

The COLREGs also standardise the lights, shapes and sound signals that let mariners identify another vessel's type, size and activity at a glance, day or night. A masthead light, sidelights and a sternlight reveal a power-driven vessel's aspect and heading; specific combinations of lights and day shapes mark vessels towing, anchored, aground, fishing or constrained by their draught. Sound signals convey intended manoeuvres and warnings. Rule 5, requiring a proper lookout at all times, and Rule 6, requiring a safe speed, underpin the whole system. Because they are internationally uniform, the COLREGs allow ships of every flag to share the same waters safely without prior communication.