Part A — General
Application
These Rules apply to all vessels on the high seas and connected waters navigable by seagoing vessels.
Responsibility
Nothing in the Rules excuses a vessel, owner, master or crew from the consequences of neglecting them, or any precaution required by ordinary practice or the special circumstances of the case.
General definitions
Defines terms used throughout the Rules — "vessel", "power-driven vessel", "sailing vessel", "vessel engaged in fishing", "seaplane", "restricted visibility" and others.
Part B — Steering and Sailing
Application
Rules 4 to 10 apply in any condition of visibility.
Look-out
Every vessel shall maintain a proper look-out by sight, hearing and all available means, appropriate to the circumstances, to make a full assessment of the risk of collision.
Safe speed
Every vessel shall proceed at a safe speed so she can take proper and effective action to avoid collision, judged against visibility, traffic density, manoeuvrability, background lights, weather and draught.
Risk of collision
Every vessel shall use all available means to determine if risk of collision exists; when in doubt, it shall be deemed to exist. Assumptions shall not be made on scanty information, especially scanty radar information.
Action to avoid collision
Any action taken shall be positive, made in ample time, and with due regard to good seamanship — a large enough course and/or speed change to be obvious to another vessel, not a small or hesitant one.
Narrow channels
A vessel proceeding along a narrow channel shall keep as near the outer limit on her starboard side as safe and practicable; vessels under 20m and sailing vessels shall not impede vessels that can only navigate within the channel.
Traffic separation schemes
Vessels using a traffic separation scheme shall proceed in the general direction of traffic flow for that lane, and shall avoid crossing lanes except as nearly as practicable at right angles.
Application
Rules 11 to 18 apply to vessels in sight of one another.
Sailing vessels
When two sailing vessels approach so as to involve risk of collision, the one with the wind on the port side keeps clear, or (same side) the windward vessel keeps clear of the leeward vessel.
Overtaking
Any vessel overtaking another shall keep clear of the vessel being overtaken — a rule that holds regardless of whether the overtaking vessel is under sail or power.
Head-on situation
When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses, each shall alter course to starboard so each passes on the other's port side.
Crossing situation
When two power-driven vessels are crossing so as to involve risk of collision, the vessel that has the other on her own starboard side shall keep out of the way.
Action by the give-way vessel
Every vessel directed to keep out of the way shall, so far as possible, take early and substantial action to keep well clear.
Action by the stand-on vessel
The stand-on vessel shall keep her course and speed, but may act to avoid collision if it becomes apparent the give-way vessel isn't taking appropriate action, or if collision cannot be avoided by the give-way vessel alone.
Responsibilities between vessels
Sets the general pecking order: power-driven vessels give way to sailing vessels, vessels NUC, RAM, fishing vessels and, where relevant, each of those to the ones above it — with exceptions in narrow channels and traffic separation schemes.
Conduct of vessels in restricted visibility
In or near restricted visibility, every vessel shall proceed at a safe speed for the conditions and be ready to manoeuvre; a vessel detecting another by radar alone shall avoid an alteration towards a vessel forward of the beam (other than when overtaking) or towards a vessel abeam or abaft the beam.
Part C — Lights and Shapes
Application
Rules in this Part apply in all weathers, and lights are to be shown from sunset to sunrise (and in restricted visibility) — day shapes by day.
Definitions
Defines each type of light — masthead light, sidelights, sternlight, towing light, all-round light, flashing light — including its colour and arc of visibility.
Visibility of lights
Sets minimum visibility ranges for lights by vessel length — from 1 nautical mile for small-craft sidelights up to 6 nautical miles for a masthead light on a vessel 50m or over.
Power-driven vessels underway
See the Lights & Shapes tool — masthead light(s), sidelights and a sternlight.
Towing and pushing
See the Lights & Shapes tool — extra masthead lights, a towing light, and a diamond day shape for a long tow.
Sailing vessels underway and vessels under oars
See the Lights & Shapes tool — sidelights and sternlight only; a cone if also under power.
Fishing vessels
See the Lights & Shapes tool — green-over-white for trawling, red-over-white for other fishing methods.
Vessels not under command or restricted in ability to manoeuvre
See the Lights & Shapes tool — red-over-red for NUC, red-white-red for RAM.
Vessels constrained by their draught
See the Lights & Shapes tool — three reds in a vertical line, a black cylinder by day (optional signal).
Pilot vessels
See the Lights & Shapes tool — white-over-red when engaged on pilotage duty.
Anchored vessels and vessels aground
See the Lights & Shapes tool — anchor lights and ball; aground adds two reds and two balls.
Seaplanes
Where a seaplane cannot show lights and shapes of the exact specifications and position in these Rules, it shall show lights and shapes as closely similar as possible.
Part D — Sound and Light Signals
Definitions
Defines "whistle", a "short blast" (about 1 second) and a "prolonged blast" (4 to 6 seconds).
Equipment for sound signals
A vessel 12m or more shall carry a whistle and a bell (and, if 100m or more, a gong); smaller vessels may carry another means of making an equally effective signal.
Manoeuvring and warning signals
One short blast = altering to starboard; two = altering to port; three = operating astern propulsion; five or more short, rapid blasts = doubt or warning; two prolonged plus one short = overtaking on the other's starboard side (with a corresponding one prolonged + one short + one prolonged as agreement).
Sound signals in restricted visibility
Prescribes fog signals by vessel type and status — e.g. a power-driven vessel making way sounds one prolonged blast at intervals of not more than 2 minutes; a vessel at anchor rings a bell rapidly for about 5 seconds every minute.
Signals to attract attention
Any light or sound signal that cannot be mistaken for a signal authorised elsewhere in the Rules may be used to attract another vessel's attention, but must not resemble a distress or aid-to-navigation signal, and should avoid high-intensity strobe lights.
Distress signals
Refers to Annex IV for the full list of distress signals — including rockets, flares, SOS, the spoken word "Mayday", and slowly raising and lowering outstretched arms.
Part E — Exemptions
Exemptions
Vessels built, or already under construction, before the Rules or a later amendment came into force are given time-limited exemptions from certain lighting and signal-equipment requirements, provided they meet the equivalent older regulations.
Part F — Verification of Compliance
Definitions
Added by a later amendment; defines terms used in the compliance-verification scheme among IMO Contracting Governments.
Application
Sets out which Contracting Governments the verification-of-compliance provisions apply to.
Verification of compliance
Contracting Governments periodically self-assess (or are audited on) how they give effect to the Convention — an administrative and governmental provision, not a rule of the road for the bridge.