COLREGs Quick Revision

What are COLREGs?

The COLREGs (Convention on the International Regulations for Preventing Collisions at Sea, 1972) are the international "rules of the road" for vessels at sea. They apply to all vessels on the high seas and connected waters navigable by seagoing vessels.

Understanding COLREGs is essential for sailing qualifications including Day Skipper, Coastal Skipper, Yachtmaster, ICC, and national certificates like Lithuanian LBS laivavedžio (skipper) exams.

Right of Way – Rule 18 Hierarchy

When two vessels meet, the stand-on vessel maintains course and speed while the give-way vessel must take early and substantial action to keep clear. Rule 18 establishes the general hierarchy:

1. Not Under Command (NUC) – vessel unable to manoeuvre due to exceptional circumstances (e.g., breakdown)
2. Restricted in Ability to Manoeuvre (RAM) – vessel restricted by the nature of her work (dredging, surveying, servicing navigation marks, etc.)
3. Vessel engaged in Fishing – actively fishing with nets, lines, trawls, or other apparatus that restricts manoeuvrability (not just transiting)
4. Sailing vessel – propelled by sail only (no engine in use)
5. Power-driven vessel – propelled by machinery

Vessels higher on the list have priority over those below. A power-driven vessel gives way to a sailing vessel, which gives way to a fishing vessel, etc.

Constrained by Draught (CBD)

A vessel constrained by her draught (Rule 18(d)) may display a cylinder by day or three all-round red lights vertically by night. However, CBD is a "shall not impede" obligation—it does not grant the same stand-on status as NUC or RAM. Other vessels should not impede a CBD vessel's passage, but the CBD vessel must still comply with the steering and sailing rules.

Sailing vessels meeting

• Opposite tacks: Port tack gives way to starboard tack
• Same tack: Windward vessel gives way to leeward vessel
• Cannot determine other's tack: Keep clear if wind is on your port side

Power-driven vessels meeting

• Head-on: Both alter course to starboard (pass port-to-port)
• Crossing: Give way to vessel on your starboard side ("if to starboard red appear, it is your duty to keep clear")
• Overtaking: Overtaking vessel keeps clear regardless of type

Navigation Lights

Lights must be shown from sunset to sunrise and in restricted visibility. Key lights to know:

Basic lights (all vessels)

Common vessel types

• Power-driven vessel under 50m: Masthead light + sidelights + stern light
• Power-driven vessel 50m+: Two masthead lights (second higher aft) + sidelights + stern light
• Sailing vessel: Sidelights + stern light (no masthead light)
• Vessel at anchor: All-round white light (two if 50m+)
• Not Under Command: Two all-round red lights vertically
• Restricted Ability to Manoeuvre: Red-white-red vertically
• Constrained by Draught: Three all-round red lights vertically
• Trawler (engaged in trawling): Green over white + sidelights + stern light when making way
• Fishing (other than trawling): Red over white + sidelights + stern light when making way
• Pilot vessel on duty: White over red at masthead

Day Shapes

Black shapes displayed during daylight indicate a vessel's status:

• Ball: Vessel at anchor
• Two balls vertically: Not Under Command (NUC)
• Ball-diamond-ball vertically: Restricted in Ability to Manoeuvre (RAM)
• Cylinder: Constrained by Draught (CBD)
• Cone apex down: Sailing vessel using engine (motor-sailing)
• Two cones apexes together (diamond shape): Vessel engaged in fishing
• Two cones apexes together + cone apex up: Fishing vessel with gear extending more than 150m (cone points in direction of gear)

Sound Signals

Sound signals communicate manoeuvres and warnings. A "short blast" is about 1 second; a "prolonged blast" is 4–6 seconds.

Manoeuvring signals (in sight of one another)

• One short: I am altering course to starboard
• Two short: I am altering course to port
• Three short: I am operating astern propulsion
• Five or more short: Warning / I do not understand your intentions

Overtaking in narrow channel (Rule 34(c))

• Two prolonged + one short: I intend to overtake on your starboard side
• Two prolonged + two short: I intend to overtake on your port side
• Prolonged-short-prolonged-short: Agreement to being overtaken

Restricted visibility signals (Rule 35)

• One prolonged (≤2 min intervals): Power-driven vessel making way
• Two prolonged (≤2 min): Power-driven vessel underway but stopped
• One prolonged + two short (≤2 min): Sailing vessel, fishing, towing, NUC, RAM, CBD
• Bell (5 seconds, every minute): Vessel at anchor under 100m
• Bell forward + gong aft: Vessel at anchor 100m+

Narrow Channels & Traffic Separation Schemes

• Keep to the starboard side of narrow channels
• Vessels under 20m and sailing vessels shall not impede vessels that can only navigate safely within the channel
• In Traffic Separation Schemes: use the appropriate lane, join/leave at shallow angles, cross at right angles if necessary
• Do not anchor in traffic lanes except in emergency

IALA Buoyage – Region A (Europe)

In IALA Region A (Europe, including Lithuania, and most of the world except the Americas, Japan, Korea, and Philippines):

• Lateral marks when returning from sea: Red marks to PORT, green marks to STARBOARD
• This is opposite to IALA Region B (Americas, etc.) where red is to starboard when returning

Cardinal marks indicate where safe water lies relative to the mark (N, E, S, W) and are the same in both IALA regions.

Memory Aids

• "If to starboard red appear, it is your duty to keep clear" – you see another vessel's port (red) side light, you must give way
• "Green to green, red to red, perfect safety, go ahead" – passing safely with sidelights aligned
• "NUC = two reds" – two all-round red lights vertically
• "RAM = red-white-red" – three lights vertically
• "Trawler = green over white" – trawling at night
• "Fishing = red over white" – fishing (other than trawling)

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Related Guides

• CEVNI Inland Waterway Rules – rules for rivers, canals, and lakes
• COLREG — szybka powtórka (Polish)
• Buriavimo egzaminas Lietuvoje (Lithuanian)