COLREGS Rules: Give-Way, Lights, Signals, and Inland Differences

The COLREGS rules — formally the International Regulations for Preventing Collisions at Sea — are the global “rules of the road” that govern how every vessel on the water navigates around every other. Adopted by the International Maritime Organization in 1972 and in force since July 15, 1977, the 38 rules cover lookout duties, safe speed, right-of-way, lights and shapes, sound signals, and conduct in fog.¹ The United States made them binding on U.S.-flagged vessels through the International Navigational Rules Act of 1977.²

Where the Rules Apply

Rule 1 makes COLREGS apply to all vessels on the high seas and in all connected waters navigable by seagoing vessels.³ That reaches everything from a container ship crossing the Pacific to a recreational sailboat outside a harbor entrance. Local authorities can create special rules for harbors and inland waterways, but those rules must conform as closely as possible to the international standard.

In U.S. waters, the Coast Guard has drawn “COLREGS Demarcation Lines,” published in 33 CFR Part 80, that mark where international waters end and inland waters begin. Outside those lines you follow the International Rules. Inside them you follow the U.S. Inland Navigation Rules.² The two systems are broadly similar but differ in several places that matter, especially whistle signals and certain lights.

The Core Duties Every Vessel Owes

Before any right-of-way rule kicks in, every vessel operator owes a set of baseline duties. Rule 2 holds that no vessel, owner, or crew member is excused from the consequences of ignoring the rules or neglecting ordinary good seamanship. That standard carries real legal weight: you’re expected to use professional judgment even when no specific rule addresses your exact situation. Rule 2 also lets a mariner depart from the rules to avoid immediate danger, but the burden is on you to show that following them would have made things worse.

Rule 5 requires a proper lookout at all times, using sight, hearing, and every other available means, including radar and AIS.⁴ A proper lookout means a dedicated person scanning the horizon, not a captain glancing up from a chart every few minutes.

Rule 6 requires a safe speed so the vessel can stop or maneuver effectively in the current conditions.⁵ There is no fixed number. Safe speed depends on visibility, traffic density, sea state, wind, and how quickly your vessel can turn or stop. A speed that felt fine on open ocean can be dangerous in fog or crowded water.

Rule 7 tells you how to test for collision risk. If the compass bearing of an approaching vessel doesn’t change over time, you’re on a collision course.⁶ Any doubt is resolved by assuming the risk is real. Rule 7 also warns against relying on incomplete radar data to conclude you’re clear.

Rule 8 governs the response. Any action must be decisive, made early, and large enough for the other vessel to see. Small last-minute course tweaks are exactly what the rules are built to prevent.³

Who Gives Way to Whom

Rules 11 through 18 assign right-of-way when vessels are in visual contact. The moment you can no longer see the other vessel, these rules stop applying and Rule 19 (restricted visibility) takes over.

Head-On

Rule 14 covers two power-driven vessels approaching roughly bow-to-bow. Both turn to starboard and pass port-side to port-side.⁷ If there’s any doubt about whether the situation is head-on, treat it as head-on and turn to starboard.

Crossing

Rule 15 covers two power-driven vessels on crossing paths. The vessel that sees the other on its starboard side is the give-way vessel and must avoid crossing ahead.⁸ Simplest way to hold onto it: if the other vessel is on your right, you give way.

Overtaking

Rule 13 is absolute. Any vessel overtaking another must keep clear, regardless of type. You’re overtaking when you approach from a direction more than 22.5 degrees behind the other vessel’s beam, meaning at night you’d see its stern light and neither sidelight.⁹ If you can’t tell whether you’re overtaking or crossing, assume you’re overtaking. Once that duty attaches, no later change in bearing relieves you until you’re completely past.

Two Sailing Vessels

Rule 12 handles two sailing vessels approaching each other. If the wind is on different sides of the two boats, the vessel with the wind on its port side gives way. If the wind is on the same side, the windward (upwind) vessel gives way to the leeward one. A vessel on port tack that can’t tell which tack a windward vessel is on must give way.

What Give-Way and Stand-On Actually Require

Rules 16 and 17 spell out the conduct expected of each role. The give-way vessel takes early, substantial action to stay well clear; the other operator has to be able to see what you’re doing. The stand-on vessel holds course and speed so the give-way vessel can predict where it will be. If the give-way vessel obviously isn’t acting, the stand-on vessel may maneuver on its own, and once collision can no longer be avoided by give-way action alone, the stand-on vessel is required to take whatever action best avoids it. Waiting too long while trusting the other operator to act is one of the most common mistakes in collision cases.

Vessel Priority

Rule 18 sets a hierarchy based on maneuverability: the less able a vessel is to get out of the way, the more protection it gets.¹⁰

Vessels not under command (disabled, unable to maneuver) sit at the top; everyone else keeps clear.
Vessels restricted in their ability to maneuver (dredging, cable-laying, mine-clearing) come next.
Vessels engaged in fishing with nets or trawls rank above sailing and power-driven vessels.
Sailing vessels rank above power-driven vessels.
Power-driven vessels give way to all of the above.
Seaplanes on the water must keep well clear of all vessels.
Wing-in-ground (WIG) craft taking off, landing, or flying near the surface keep clear of everyone; on the water they follow power-driven vessel rules.¹⁰

Three things override the hierarchy: narrow-channel rules (Rule 9), traffic separation schemes (Rule 10), and overtaking (Rule 13). A sailboat overtaking a tanker in a narrow channel does not suddenly gain right-of-way because it’s under sail. Rule 9 also requires vessels in a narrow channel to keep as close to the starboard edge as is safe and practical, and requires small vessels, sailing vessels, and fishing boats not to impede larger vessels that can only navigate safely within the channel.³

Navigating in Fog and Restricted Visibility

Rule 19 governs whenever vessels cannot see each other, whether from fog, heavy rain, snow, or similar conditions. It applies as you approach a fog bank, not only once you’re in it. Every vessel operates at a safe speed for the conditions and has engines ready for immediate maneuvering.

When you detect another vessel by radar alone and a close-quarters situation is developing, act early. Two specific restrictions apply: don’t turn to port for a vessel that’s ahead of your beam unless you’re overtaking it, and don’t turn toward a vessel that’s alongside or behind your beam. Turning toward an unseen vessel, or turning port when the other vessel expects starboard, sharply raises collision risk.

If you hear a fog signal that seems to come from ahead, reduce to the minimum speed needed to maintain steerage. Stop entirely if necessary and navigate with extreme caution until the danger passes.

Reading Another Vessel: Lights and Shapes

Rules 20 through 31 set out the visual signals a vessel must display. Lights are required from sunset to sunrise and during any period of restricted visibility. Shapes — balls, cones, diamonds, and cylinders — communicate the same information during daylight.

Rule 21 defines the standard set. Sidelights consist of a green light on the starboard side and a red light on the port side, each visible across a 112.5-degree arc from dead ahead to just past the beam.¹¹ A white masthead light sits higher and forward on power-driven vessels, and a white stern light covers the arc behind. Read together, those lights let an observer determine another vessel’s heading and whether risk of collision exists at a glance.

Special combinations show status:

Not under command: two red all-round lights vertically at night, or two black balls by day.¹²
Restricted in ability to maneuver: red, white, red vertically at night, or a ball-diamond-ball arrangement by day.¹²
Vessel engaged in fishing: red over white vertically, or two cones point-to-point by day.
Sailing vessel under way: sidelights and stern light, no masthead light.

Sound Signals and the Danger Signal

Rules 32 and 33 set out required sound equipment. Vessels 12 meters or longer must carry a whistle. At 20 meters, add a bell. At 100 meters, add a gong with a tone distinct from the bell.

Under the International Rules, whistle signals announce what a vessel is doing right now. One short blast means altering course to starboard. Two short blasts means altering course to port. Three short blasts means operating astern propulsion.¹³

The signal every mariner needs to recognize instantly is the danger signal: at least five short, rapid blasts, sounded whenever a vessel is in doubt about what the other is doing or believes the other isn’t taking sufficient action to avoid collision.¹⁴ Five rapid light flashes may back it up. If you hear five blasts, something has gone wrong and you need to reassess immediately.

Rule 35 requires fog signals in restricted visibility so vessels can announce their presence to traffic they can’t see, with different cadences for power-driven vessels making way, power-driven vessels stopped, and sailing, fishing, or restricted vessels. Rule 37 reserves distress signals — including continuous sounding of a fog-signal device — for genuine life-threatening emergencies; using them for any other purpose is prohibited.

International vs. U.S. Inland: The Differences That Trip People Up

U.S. boaters inside the COLREGS Demarcation Lines follow the Inland Navigation Rules, not the International Rules. The two systems share structure and most requirements, but a few differences catch operators off guard.²

The biggest difference is whistle signals. Internationally, one short blast means “I am altering course to starboard” — a report of what the vessel is doing. Under Inland Rules, one short blast means “I intend to leave you on my port side” — a proposal that requires the other vessel to answer with the same signal if it agrees, or sound the danger signal if it doesn’t. International signals report; Inland signals negotiate.¹³

Lighting rules also differ. Inland Rules let vessels lower lights briefly to pass under bridges, permit a yellow flashing light on towing vessels that has no international equivalent, and set specific requirements for barges. Inland Rules recognize a flashing strobe as a distress signal; International Rules do not. Using the wrong signal in the wrong waters creates exactly the confusion these rules are meant to prevent.

Penalties, the Pennsylvania Rule, and Reporting

A COLREGS violation can draw a civil penalty of up to $18,610 per violation under 33 U.S.C. § 1608, assessed against the operator or the vessel, and adjusted for inflation over time.¹⁵ The Coast Guard enforces through inspections, boardings, and post-incident investigations.

When a violation is tied to a collision, the exposure widens. Courts apply the Pennsylvania Rule, from the 1874 Supreme Court decision of the same name, which creates a presumption of fault against any vessel violating a safety statute at the time of a collision.¹⁶ The violating vessel must then prove not just that the violation probably didn’t cause the collision but that it couldn’t have. Failing that standard can mean full liability for damages, environmental cleanup, and injuries.

After a collision or other serious marine incident, the owner, operator, or person in charge must file a written report on Coast Guard Form CG-2692 within five days.¹⁷ Reportable events include death, serious injury, significant property damage, or hazards to navigation. An initial verbal notification to the nearest Coast Guard sector should happen as soon as possible, before the five-day written deadline. Preserve evidence: photographs, GPS logs, radar recordings, and AIS data become critical if the incident leads to litigation or a Coast Guard investigation.

1
International Maritime Organization. Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs)
2
United States Coast Guard. Rules of the Road
3
International Maritime Organization. COLREG – Preventing Collisions at Sea
4
eCFR. 33 CFR 83.05 – Look-out (Rule 5)
5
eCFR. 33 CFR 83.06 – Safe Speed (Rule 6)
6
eCFR. 33 CFR 83.07 – Risk of Collision (Rule 7)
7
Office of the Law Revision Counsel. 33 USC 2014 – Head-on Situation (Rule 14)
8
eCFR. 33 CFR 83.15 – Crossing Situation (Rule 15)
9
eCFR. 33 CFR 83.13 – Overtaking (Rule 13)
10
eCFR. 33 CFR 83.18 – Responsibilities Between Vessels (Rule 18)
11
United States Coast Guard Navigation Center. Navigation Rules – Rules 20-31
12
eCFR. 33 CFR 83.27 – Vessels Not Under Command or Restricted in Their Ability to Maneuver (Rule 27)
13
United States Coast Guard. USCG Amalgamated Navigation Rules International and U.S. Inland
14
eCFR. 33 CFR 83.34 – Maneuvering and Warning Signals (Rule 34)
15
Federal Register. Civil Monetary Penalty Adjustments for Inflation
16
Justia. The Pennsylvania, 86 U.S. 125
17
eCFR. 46 CFR 4.05-10 – Written Report of Marine Casualty