Rules of the Road

Give-Way and Stand-On Vessels

Every vessel interaction under COLREGS assigns one vessel the responsibility to give way and the other to stand on. These two roles have specific, mandatory behaviors — and understanding them is the foundation of collision avoidance.

The give-way vessel is required to take early and substantial action to keep well clear. 'Early' means acting before the situation becomes close; 'substantial' means altering course or speed in a way that is obvious to the other vessel. A small alteration of 5 degrees made at the last moment is not substantial — it may not even be visible to the other vessel. The give-way vessel should make its maneuver unambiguous.

The stand-on vessel is required to maintain its course and speed. This is not passive permission to continue — it is an obligation. A stand-on vessel that alters course or speed unnecessarily makes the interaction unpredictable and may actually create the collision that the rules are designed to prevent. The other vessel is counting on the stand-on vessel's behavior to be predictable.

The escape clause (Rule 17): if the give-way vessel is clearly not acting to avoid collision and risk of collision exists, the stand-on vessel is then permitted — and eventually required — to take action to avoid collision by its own maneuver alone. At that point, if possible, the stand-on vessel should not alter to port toward the give-way vessel on the port side.

Vessel Hierarchy: The Order of Right of Way

COLREGS establishes a hierarchy of vessels based on their ability to maneuver. Vessels that are less maneuverable have greater right of way. This is the sequence from highest to lowest priority:

1. Vessel Not Under Command (NUC): a vessel unable to maneuver as required by the rules due to exceptional circumstances (engine failure, loss of steering, broken rudder). Displays two red lights vertically, or two black balls by day.

2. Vessel Restricted in Ability to Maneuver (RAM): a vessel that by the nature of its work is restricted in its ability to maneuver — includes dredgers, cable-laying vessels, mine-clearance vessels, and vessels conducting replenishment at sea. Displays red-white-red lights vertically, or ball-diamond-ball by day.

3. Vessel Constrained by Draft (CBD): a power-driven vessel that due to its deep draft in relation to available channel depth cannot deviate from its course. Displays three red lights vertically, or a cylinder by day. Note: this category applies only in international rules, not inland.

4. Vessel Engaged in Fishing: a vessel that is actively fishing with gear that restricts maneuverability (trawls, nets) — not a recreational vessel with a fishing pole. Displays two lights green-over-white (trawling) or red-over-white (other fishing), or a cone pointing down by day.

5. Sailing Vessel Under Sail: a vessel proceeding under sail only, with no engine assistance. The moment a sailing vessel starts its engine and uses it for propulsion — even if sails are set — it becomes a power-driven vessel for the purposes of the rules.

6. Power-Driven Vessel: all other vessels under engine power, including sailboats under engine. At the bottom of the hierarchy but still with rights against vessels above it — the hierarchy runs both directions.

Critical nuance: a sailing vessel is not the sovereign of the sea. Rule 18 specifies that sailing vessels must still keep clear of NUC, RAM, CBD, and fishing vessels. And Rule 9 and 10 override the general hierarchy in narrow channels and traffic separation schemes.

The Three Encounter Types

COLREGS defines three specific encounter situations between vessels in sight of each other, each with prescribed rules for who gives way and what action is required.

Head-On (Rule 14): two power-driven vessels meeting on reciprocal or nearly reciprocal courses such that there is risk of collision. Both vessels are required to alter course to starboard, so each passes the other on its port side. This is the only rule where both vessels simultaneously give way. The rule applies when vessels are approaching 'end-on or nearly end-on' — when neither vessel's masthead light is visible with a clear bearing preference to one side. When in doubt about a head-on vs. crossing situation, treat it as head-on and alter to starboard.

Crossing (Rule 15): two power-driven vessels crossing such that risk of collision exists. The vessel that has the other on its starboard side is the give-way vessel. It must take action to avoid passing ahead of the stand-on vessel. A useful memory aid: imagine a car at an intersection — you yield to traffic coming from your right.

Overtaking (Rule 13): any vessel overtaking another — coming up from a direction more than 22.5 degrees abaft the beam of the vessel ahead — must keep out of the way until finally past and clear. Critically: the overtaking rule applies regardless of vessel type. A sailing vessel overtaking a power-driven vessel must give way to the power-driven vessel. The overtaking vessel must keep clear and stay clear until fully past.

Sailing vessels (Rule 12): when two sailing vessels are approaching each other, the rules are different. The vessel on the port tack gives way to the vessel on the starboard tack. If both are on the same tack, the vessel to windward gives way. If the vessel on the port tack cannot determine which tack the other vessel is on (perhaps at night), it gives way to the other. These rules assume both vessels are under sail with no engine.

Narrow channels and traffic separation schemes override the general encounter rules. Rule 9 requires vessels to keep to the starboard side of a narrow channel, and a vessel that can only safely navigate in the channel has additional right-of-way protection. Traffic Separation Schemes (Rule 10) have specific requirements about how to enter, exit, and cross shipping lanes.