ColRegs Quick Reference
The International Regulations for Preventing Collisions at Sea (ColRegs) are the "rules of the road" for all vessels. This reference covers the structure, key rules, and the vessel hierarchy you need to know.
Structure of the ColRegs
Part A — General (Rules 1-3)
Application, responsibility, and general definitions. The ColRegs apply to all vessels on the high seas and connected navigable waters. Nothing in the rules exempts a vessel from the consequences of neglect.
Part B — Steering & Sailing Rules (Rules 4-19)
The core rules governing conduct of vessels in any condition of visibility, in sight of one another, and in restricted visibility. Includes look-out, safe speed, risk of collision, and the crossing/overtaking/head-on rules.
Part C — Lights & Shapes (Rules 20-31)
Requirements for navigation lights (sunset to sunrise and restricted visibility) and day shapes. Defines what every vessel type must display so others can identify their status and heading.
Part D — Sound & Light Signals (Rules 32-37)
Manoeuvring signals, sound signals in restricted visibility, and signals to attract attention. Defines short blast (1 second) and prolonged blast (4-6 seconds) patterns.
Part E — Exemptions (Rule 38)
Transitional provisions for vessels built before the current rules came into effect, allowing certain older vessels time to comply with updated light and shape requirements.
Key Encounter Scenarios
The three fundamental encounters between power-driven vessels in sight of one another. Blue = stand-on, red = give-way, green arrows = correct action.
Key Rules Summary
Look-out
Every vessel shall at all times maintain a proper look-out.
Use sight, hearing, and all available means (including radar and AIS) appropriate to the prevailing circumstances. A proper look-out is the foundation of collision avoidance — everything else depends on it.
Risk of Collision
Every vessel shall use all available means to determine if risk of collision exists.
If the compass bearing of an approaching vessel does not appreciably change, risk of collision exists. When in doubt, assume it does. Use radar plotting or ARPA if available — do not rely solely on a visual impression.
Action to Avoid Collision
Any action taken shall be positive, made in ample time, and large enough to be readily apparent.
A small alteration of course or speed is not enough — the other vessel needs to see that you have taken action. Avoid altering to port for a vessel on your port bow. A succession of small alterations should be avoided.
Sailing Vessels
When two sailing vessels approach, the vessel on port tack gives way.
When both are on the same tack, the windward vessel keeps clear. If a vessel on port tack cannot determine the other's tack, she shall keep clear. "Tack" is defined by which side the mainsail is carried — opposite to the side the wind is on.
Overtaking
Any vessel overtaking another shall keep out of the way of the vessel being overtaken.
A vessel is overtaking when coming up from more than 22.5 degrees abaft the beam (i.e., from behind the arc of the stern light). This rule overrides Rules 12, 14, and 15 — an overtaking vessel always gives way, regardless of type.
Head-on Situation
Both vessels alter course to starboard and pass port to port.
Applies when two power-driven vessels are meeting on reciprocal or nearly reciprocal courses. Each vessel alters to starboard so they pass on the port side of each other. When in doubt whether a head-on situation exists, assume it does and alter to starboard.
Crossing Situation
The vessel with the other on her starboard side shall keep out of the way.
The give-way vessel should avoid crossing ahead of the stand-on vessel. The give-way vessel should ideally alter course to starboard (passing astern) or slow down. The stand-on vessel maintains course and speed until it becomes apparent the give-way vessel is not taking action.
Action by Stand-on Vessel
The stand-on vessel shall maintain course and speed — but must act if the give-way vessel fails to.
Initially keep your course and speed. If it becomes apparent the give-way vessel is not acting, you may take action to avoid collision. If collision cannot be avoided by the give-way vessel alone, you shall take such action as will best help avoid collision. Avoid altering to port for a vessel on your port side.
Responsibilities Between Vessels
Establishes the hierarchy of vessels — who gives way to whom based on manoeuvrability.
A power-driven vessel gives way to sailing, fishing, NUC, RAM, and CBD vessels. A sailing vessel gives way to NUC, RAM, fishing, and CBD vessels. This hierarchy does not apply to overtaking (Rule 13) or vessels in narrow channels (Rule 9) or TSS (Rule 10).
Hierarchy of Vessels (Rule 18)
Vessels higher in this hierarchy have right of way over those below. The logic: the less manoeuvrable a vessel is, the more other vessels must keep clear.
Not Under Command (NUC)
A vessel unable to manoeuvre as required by the rules — e.g., engine failure, steering failure. Shows two all-round red lights (vertical) or two black balls by day.
Restricted in Ability to Manoeuvre (RAM)
A vessel restricted by the nature of her work — e.g., dredging, cable-laying, mine clearance, towing operations. Shows red-white-red all-round lights or ball-diamond-ball by day.
Constrained by Draught (CBD)
A vessel severely restricted by her draught in relation to the available depth of water. Shows three all-round red lights (vertical) or a cylinder by day. Only applies in international waters.
Vessel Engaged in Fishing
Vessels actively fishing with nets, lines, or trawls that restrict manoeuvrability. Does not include vessels trolling. Shows two all-round lights (red over white for trawling, red over green for other fishing) or appropriate day shapes.
Sailing Vessel
A vessel under sail alone (not using engine). The moment the engine goes on, even with sails up, the vessel is power-driven and must display a cone point-down by day.
Power-Driven Vessel
Any vessel propelled by machinery, including sailing vessels using their engine. Gives way to all categories above in the open sea.
Important: The hierarchy does not apply when overtaking (Rule 13 — the overtaking vessel always gives way), in narrow channels (Rule 9), or in traffic separation schemes (Rule 10). An overtaking power vessel must give way to the vessel she is overtaking, even if it is a dinghy.