Chapter 3: Who the Rules Apply To, and Where
The previous two chapters answered what the Rules are for and where they came from. This one answers a question that sounds simpler than it is: who has to obey the Rules, and in what waters? The honest answer has two layers. The first is what Rule 1 says on its face, which is broad and easy to state. The second is the layer that trips up officers who have read the Rules but never read how they reach a bridge. An international convention does not, by itself, oblige anyone. It binds states, not watchkeepers. The real content of this chapter is how the text in front of you becomes law that you personally must follow. That sets up the question the next chapter takes on directly: why a warship of the Royal Australian Navy holds itself to a convention it could, in strict legal theory, treat as someone else’s problem.
All vessels, almost everywhere
Rule 1(a) sets the reach of the instrument in a single sentence. The Rules apply to all vessels on the high seas and in all waters connected with them that are navigable by seagoing vessels. Two things are worth drawing out of that. The first is that the reach is defined by the water, not by the ship. The Rules do not ask what flag you fly, what you are carrying, or where you are registered. They ask only whether you are floating on water that connects to the sea and that a seagoing vessel could navigate. Wherever that is true, the Rules are in force, and they are in force for everyone on that water at once. That universal reach is the whole point. The script only works if every vessel in an encounter is reading from it. So the instrument is written to leave no vessel, and no navigable salt or connected water, outside its scope.
The second point is the qualifier “connected therewith navigable by seagoing vessels.” This is what carries the Rules off the open ocean and up into estuaries, harbours and rivers, as far inland as a seagoing ship could in principle go. Where that connection stops, and purely inland or non-tidal waters begin, a state is free to run its own regime. That is the subject of paragraph (b) below. But the default, everywhere the sea reaches, is the international rules.
TRANSLATION
Rule 1(a) (MISCPUB 0127): “These Rules shall apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels.”
Plain reading: the Rules apply to every vessel, on the sea and on any water joined to it that a seagoing ship could use.
What the legal wording does that the plain version can’t: it fixes the scope to a physical fact about the water, not to nationality, vessel type or purpose. So no vessel can argue its way out of the Rules by what it is. The reach follows the water, and the water decides, not the ship.
What counts as a vessel
If the Rules bind all vessels, then everything turns on what a vessel is. Here the drafters were deliberately broad. Rule 3(a) defines “vessel” to include every description of water craft, including non-displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water. The phrase “every description of water craft” is doing a lot of work. It takes in the container ship and the kayak, the hovercraft skimming the surface, the wing-in-ground craft flying just above it, and the seaplane sitting on it. And it does so on purpose. Cockcroft and Lameijer note (7th ed, comment on Rule 1) that seaplanes, non-displacement craft and WIG craft are all included in the definition, and are therefore to be treated as power-driven vessels for the purposes of the Rules, except where a specific rule provides otherwise.
The reason for such breadth is the same predictability argument that runs through the whole instrument. A set of collision rules is only as strong as its weakest exclusion. If the OOW were free to decide that some object on the water was not really a vessel, and so outside the Rules, the system would have a gap in it exactly where judgement is least reliable: in the moment of an unfamiliar encounter. So the definition is drawn wide enough that the question almost never comes up. The practical discipline that follows is simple. You do not get to rule something out of the encounter because it is unusual. If it is on the water and could carry someone or something, treat it as a vessel and apply the Rules, until a specific provision tells you to do otherwise.
PRACTICAL NOTE: the breadth is a safeguard, not a technicality
The wide definition exists so that the strange contact is inside the system, not outside it. A WIG craft closing at high speed, a seaplane taxiing across your bow, a barge under tow with no obvious means of propulsion of its own: none of these are edge cases to be reasoned away. The Rules expected them, and defined “vessel” to reach them. When something on the water does not fit your mental picture of a ship, that is exactly when the breadth of Rule 3(a) is protecting you.
Where the international rules stop and local rules begin
Rule 1 then makes room for special rules, and an OOW needs to know how that room is bounded. Paragraph (b) provides that nothing in the Rules interferes with special rules made by an appropriate authority for roadsteads, harbours, rivers, lakes or inland waterways connected to the high seas, provided those special rules conform as closely as possible to the international ones. This is how a port or harbour authority can layer local requirements over the top of the COLREGs. Cockcroft and Lameijer point out (7th ed, comment on Rule 1) that a roadstead, an open anchorage less sheltered than a harbour, is expressly included. This means local rules can reach water lying outside the usual limits of inland waters. They also note that special rules on lights, sound signals and other aspects of collision avoidance are in force in many ports, rivers, canals and inland waters around the world. The final sentence of paragraph (b), insisting on conformity, exists to keep those local regimes close enough to the international ones that a visiting mariner is not caught out.
The consequence on the bridge is that the international rules do not switch off when you enter such waters. The local rules sit on top of them, and must resemble them. But “must resemble” is not “must be identical,” and the differences are where the trouble is. The defence against it is preparation, not improvisation. The Sailing Directions and the relevant port publications set out the local regime. They are to be read before arrival, not discovered on the way in.
Paragraphs (c) to (e) handle three narrower cases. Paragraph (c) preserves a government’s right to prescribe additional station or signal lights, shapes or whistle signals for warships and vessels proceeding under convoy, and additional lights or shapes for fishing vessels fishing as a fleet. It sets a firm condition: these extra signals must, so far as possible, not be capable of being mistaken for any light, shape or signal authorised elsewhere in the Rules. The point of that condition is to prevent confusion in the signalling system. A navy may add to it, but may not introduce anything another mariner could misread as a standard signal. Paragraph (d) gives the Organization, the IMO, authority to adopt traffic separation schemes for the purposes of the Rules. That is the provision that gives Rule 10 its authority. Paragraph (e) allows a government to let a vessel of special construction or purpose, one that physically cannot carry lights, shapes or sound equipment in the standard number, position or arc, comply as closely as her government determines is possible. Each of these repeats the idea of paragraph (b) on a smaller scale. The international standard holds, and any departure from it is bounded by a duty to stay as close to the standard as the situation allows.
DRAFTING ISSUE: “Conform as closely as possible” and “so far as possible”
Rule 1 leans repeatedly on qualified language. Special rules shall conform “as closely as possible.” Additional signals shall “so far as possible” not be mistakable. Special-construction vessels shall achieve the “closest possible compliance.” None of these phrases draws a hard line, and that is deliberate, for the reasons Chapter 6 sets out. They set a direction of travel rather than a fixed threshold: get as near the standard as you reasonably can, and carry the burden of justifying any distance you fall short. For the OOW the practical reading is that a local or special arrangement is never licence to depart freely from the international scheme. It is permission to differ only as far as genuine necessity requires.
How an international convention reaches your bridge
Here is the part the text on its own will not tell you. The document in front of you is the 1972 Convention on the International Regulations for Preventing Collisions at Sea. A convention is an agreement between states. In strict legal terms it binds the governments that are party to it, and it obliges those governments to bring their own shipping into line. It does not reach down and place a direct duty on an individual watchkeeper. So if the Rules bound no one but governments, the OOW on a given bridge could fairly ask what any of it has to do with them personally. The answer is that each contracting state closes that gap itself. It takes the Convention into its own domestic law, and applies it to ships that fly its flag wherever in the world they are, and to foreign ships while they are in its waters. The Convention sets the standard. National law is what makes the standard apply on a real bridge.
Australia does exactly this. Australia is a party to the 1972 Convention (it is one of the contracting states listed in the IMO’s status of multilateral conventions). It gives the Rules force in domestic law mainly through the Navigation Act 2012 and the marine order made under it, Marine Order 30 (Prevention of collisions) 2016. That order applies the COLREGs to shipping and makes it an offence for an owner or master to operate a vessel in breach of them. The Australian Maritime Safety Authority administers and enforces that regime. The effect for civil shipping is that the Rules are not merely an international courtesy or a matter of good practice. They are Australian law, and breach of them carries legal consequence. When you read MISCPUB 0127, you are reading a treaty. But the reason it governs your conduct is that your own state has enacted it.
This is the cleanest way to hold the whole question in your head. The Rules apply to all vessels on the relevant waters because Rule 1(a) says so. They reach you personally because your flag state has made the Convention into law you are bound by. For the great majority of vessels you will ever meet, that is the full chain, and it ends in a clear legal duty. The warship sits at a different point in this chain, and that difference is the subject of the next chapter.
A short worked case: crossing into harbour limits
To make the territorial part concrete, take a ship inbound to a major Australian port. Ten miles off the coast she is on waters connected to the high seas and navigable by seagoing vessels. So the international rules apply in full, and apply equally to every other vessel around her. As she closes the coast and enters the harbour limits, she crosses into water for which the port authority has made special rules under Rule 1(b). Perhaps a vessel traffic service with mandatory reporting points, a local speed restriction, or specific signals for vessels over a certain size. The international rules do not turn off at that line. They keep governing the encounter geometry exactly as before, and the local rules, which by Rule 1(b) must conform as closely as possible to them, sit on top. What changes is that the OOW is now bound by two regimes at once, and must have read the local one in advance, from the Sailing Directions and port publications, rather than meeting it for the first time on the chart. The lesson is that “where do the Rules apply” is not an academic question. The answer changes what you are legally bound by as you cross a line drawn on the water. And the only safe way to cross that line is to already know what is on the other side of it.
See also: Ch 4 (why a warship follows the Rules, and how the chain differs for the RAN), Ch 5 (the architecture of Parts A–F and the Annexes), Ch 7 (the defined terms of Rule 3, treated in full as the vocabulary of the Rules).