IRPCAS / Collision Regulations

The International Regulations for Preventing Collisions at Sea (IRPCAS, also known as COLREGs) are a set of 41 rules published by the International Maritime Organization (IMO). They apply to all vessels on the high seas and connected navigable waters.

The regulations are divided into five parts:

• Part A — General (Rules 1–3): application, responsibility, definitions
• Part B — Steering & Sailing Rules (Rules 4–19): conduct in any visibility, restricted visibility
• Part C — Lights & Shapes (Rules 20–31): what to display and when
• Part D — Sound & Light Signals (Rules 32–37): manoeuvring, warning, fog signals
• Part E — Exemptions (Rule 38)

Every skipper, helm, and crew member should have a working knowledge of IRPCAS. Even small dinghies must comply when sharing water with other vessels.

The “Rule of the Road” determines which vessel must give way (alter course or slow down) and which must stand on (maintain course and speed). The hierarchy of right of way, from most to least protected:

1. Not Under Command (NUC) — vessel unable to manoeuvre
2. Restricted in Ability to Manoeuvre (RAM) — e.g. dredger, cable layer
3. Constrained by Draught (CBD) — deep-draught vessel in a narrow channel
4. Vessel engaged in Fishing — actively fishing with nets/trawl
5. Sailing vessel — under sail alone (no engine)
6. Power-driven vessel — including sailing boats using their engine

Between two power-driven vessels:

• Head-on (Rule 14): Both alter course to starboard so they pass port-to-port.
• Crossing (Rule 15): The vessel that has the other on her starboard side must give way. Remember: “If to starboard red appear, it is your duty to keep clear.”
• Overtaking (Rule 13): The overtaking vessel always gives way, regardless of type.

Between two sailing vessels (Rule 12):

• A vessel on port tack gives way to one on starboard tack.
• When on the same tack, the windward boat gives way to the leeward boat.
• If you cannot determine the other vessel’s tack, assume you must give way.

Sound signals communicate a vessel’s intentions or status, particularly in close-quarters situations or restricted visibility. A short blast lasts about 1 second; a prolonged blast lasts 4–6 seconds.

If you hear 5+ short blasts, the other vessel is alarmed. Check your situation immediately and take avoiding action if needed.

During daylight, vessels display black shapes hoisted in the rigging to indicate their status. These shapes are visible from a distance and tell other mariners what type of vessel you are or what activity you are engaged in.

At night, these shapes are replaced by specific light configurations. For example, a vessel NUC shows two all-round red lights in a vertical line instead of two balls.

Rule 19 governs conduct in restricted visibility (fog, heavy rain, snow, mist). It applies when vessels cannot see each other visually, regardless of radar contact.

Key obligations in restricted visibility:

• Proceed at a safe speed adapted to the conditions (Rule 6).
• Have engines ready for immediate manoeuvre.
• Sound the appropriate fog signals (Rule 35).
• Use radar if fitted to maintain a proper lookout.
• If you detect another vessel by radar alone, determine if a close-quarters situation is developing.

Critical actions if you hear a fog signal forward of your beam:

1. Reduce speed to the minimum at which you can maintain course.
2. If necessary, take all way off (stop).
3. Navigate with extreme caution until danger of collision is over.

Fog signal intervals: