IRPCS: International Regulations for Preventing Collisions at Sea

Snapshot Rules 1 to 3 This is the opening section of the IRPCS. It outlines who the rules apply to and how they can be adapted to local requirements. It introduces different vessel types and their definitions, giving some examples. It outlines the difference between being at sea (underway) versus at anchor or moored up. It also defines the term restricted visibility, referring to some causes of reduced visibility but stopping short of explaining how far you must be able to see before being considered restricted.

Snapshot Rules 4 to 19 This is the bit that everyone needs to know. It’s divided into three sections and is the only subdivided part of the rule book. Each section focuses on our ability to see one another (or not): Section I – Conduct of vessels in any conditions of visibility (rules 4 to 10), Section II – Conduct of vessels in sight of one another (Rules 11 to 18), Section III – Conduct of vessels in restricted visibility (Rule 19). Each section starts with a rule outlining the visibility conditions under which the rules apply.

Snapshot Rules 1 to 10 Section I applies in any visibility condition, meaning it always remains in force. It covers our core obligations always to maintain a proper lookout and travel at a speed at which we can remain safe, accounting for the conditions. It outlines our responsibility to act in a timely and significant enough manner when taking actions to avoid collisions.

Snapshot Rules 11 - 18 The second section of Part B focuses on when vessels can see one another. Importantly, this is anytime other than when conditions are creating restricted visibility. This is where we learn about hierarchy, and each vessel’s obligations should their paths cross. The hierarchy is based mainly on manoeuvrability, with the guiding principle that a more manoeuvrable vessel can avoid a less manoeuvrable one. It also outlines what each should do if two of the same type come together.

Snapshot Rule 19 This section contains specific instructions for what to do in restricted visibility. The last section of Part B, Section III, only contains one rule–nineteen. This refers to what vessels should do in or near areas of restricted visibility. Whilst the previous rules don’t give any vessel the right of way, this rule replaces the rules in Section II (rules 11 to 18) and removes the stand-on and give-way concept.

Snapshot Rules 20 to 31 This part defines the lights and shapes each type of vessel must display. Lights serve three distinct purposes; – Presence – awareness of a vessel, – Heading – which way the vessel is travelling, – Status – any special status the vessel has. Shapes are the daytime equivalent of status lights. Black, three-dimensional geometric shapes, usually hoisted on a mast.

Snapshot Rules 32 to 37 This part outlines the rules for the sounds used when signalling manoeuvres and during restricted visibility (fog signals). Bells, gongs, whistles and lights make up the various combinations of signals available. However, most of the time, the only signal we'll use or hear is a whistle. Unfortunately, the term whistle is a little misleading, as it refers to any sound signalling appliance, usually a horn. Bells and gongs are reserved for longer vessels to indicate their length when anchored in restricted visibility. Signals are broken into three categories: Manoeuvring & warning These signals are focused on communication. They allow vessels to communicate their intentions, ask a question of another vessel, or reply to confirm their understanding of the situation. Restricted visibility The sound signals used in restricted visibility replace what would otherwise be visible by day, using shapes, or night using lights. The rule book's definitions and application fundamentally change in restricted visibility Attracting attention & distress Lastly, are signals used to attract attention or indicate distress. The distress signals are found in annex IV of the rules, which includes the Mayday message, VHF DSC, and EPRIB, among some of the more old-fashioned methods.

Snapshot Rule 38 This short part of the IRPCS contains some notable references to exemptions for vessels built or commissioned before specific rule changes.

Snapshot Rules 39 to 41 Part F is aimed at the governing bodies that have adopted the IRPCS and their willingness to be audited, providing transparency.

The Annexes of the International Regulations for Preventing Collisions at Sea (IRPCS) supplement the main rules and provide detailed technical and operational specifications to ensure safe navigation and prevent collisions. These annexes address specific areas of maritime operations and equipment requirements, supporting the practical implementation of the Colregs.The international COLREGs have four annexes, I–IV. Pilot vessels are covered by Rule 29 in Part C. See the IMO convention overview.These annexes are essential for mariners, shipbuilders, and regulators to ensure that vessels meet the technical and operational requirements to maintain sea safety.

Annex I: Positioning and Technical Details of Lights and Shapes Specifies the placement, range, visibility, and technical details of navigation lights and day shapes required by the IRPCS. Ensures consistency and compliance for vessels of different sizes and designs.

Annex II: Additional Signals for Fishing Vessels Fishing in Close Proximity Outlines specific signals fishing vessels use to communicate their activities and avoid collisions while operating in close quarters.

Annex III: Technical Details of Sound Signal Appliances Provides specifications for sound signalling devices, including their construction, audibility range, and operation requirements.

Annex IV: Distress Signals Lists the internationally recognised signals that indicate a vessel is in distress and requires assistance. Includes visual, auditory, and electronic signals like flares, flags, radio transmissions, and flashing lights.