COLREGS Reference
Rules of the Road
All 38 COLREGS rules with plain-language summaries, lights and shapes tables, sound signals, and USCG license exam tips. Based on the International Regulations for Preventing Collisions at Sea, 1972 (72 COLREGS) and the U.S. Inland Navigation Rules.
Authority: 33 U.S.C. § 1602 (COLREGS) and 33 U.S.C. § 2001 (Inland Rules). Official USCG text (PDF)
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Part A — General
Rule 1 — Application
The International Regulations (COLREGS) apply to all vessels on the high seas and connecting waters navigable by seagoing vessels. The Inland Rules apply on specified U.S. inland waters. When both apply, COLREGS controls on the high seas; Inland Rules control inside the Demarcation Lines.
Exam tip
The primary exam trap: Inland Rules apply inside U.S. demarcation lines, COLREGS outside. Know the dividing line for your home waters.
Rule 2 — Responsibility
Rule 2 is the 'good seamanship' rule. Every vessel must observe the Regulations, but may depart from them to avoid immediate danger. This is the 'General Prudential Rule' — compliance is required except when danger makes departure necessary. Ignorance of the rules is never an excuse.
Exam tip
Rule 2 allows departure from the rules ONLY to avoid immediate danger — not for convenience. The burden is on the vessel departing.
Rule 3 — General Definitions
Defines key terms: 'vessel' (any watercraft), 'power-driven vessel' (propelled by machinery), 'sailing vessel' (using sails only — engine off or not fitted), 'vessel not under command' (NUC — unable to maneuver due to exceptional circumstance), 'vessel restricted in ability to maneuver' (RAM — limited by nature of work), 'vessel constrained by draught' (COLREGS only — not in Inland), 'underway' (not anchored, aground, or made fast to shore), 'making way' (underway AND moving through water).
Exam tip
Underway ≠ making way. A vessel can be underway (not anchored) but not making way (no headway). This affects light requirements.
Part B — Steering and Sailing Rules
Rule 4 — Application (Section I)
Section I rules (4–10) apply in any condition of visibility.
Rule 5 — Look-out
Every vessel shall at all times maintain a proper look-out by sight and hearing, and by all available means appropriate to the circumstances. 'All available means' includes radar, AIS, VHF, and visual watch. A radar watch alone is insufficient.
Exam tip
Top exam topic: a proper lookout is ALWAYS required — not just in restricted visibility. Radar does not substitute for a visual watch in clear conditions.
Rule 6 — Safe Speed
Every vessel must proceed at a safe speed at all times, taking into account: visibility, traffic density, maneuverability, the presence of vessels in the vicinity, the state of wind/sea/current, proximity of navigational hazards, and (at night) the background of shore lights. A vessel with radar must also consider its radar characteristics, any constraints of the radar scale in use, and the effect of sea state on radar detection.
Exam tip
Safe speed is NOT a fixed number. It is determined by circumstances. A vessel in fog at 20 knots may be violating Rule 6 even if moving slower than a vessel in clear visibility.
Rule 7 — Risk of Collision
Risk of collision exists if the compass bearing of an approaching vessel does not appreciably change. Use all available means: radar ranging and bearing, compass bearing observations. When in doubt — risk exists. A vessel shall not assume risk does not exist based solely on a small compass bearing change or when appreciable bearing change is evident only from a very close range.
Exam tip
Steady compass bearing = risk of collision. Even if bearing changes slightly, risk may still exist if range is decreasing rapidly.
Rule 8 — Action to Avoid Collision
Action taken to avoid collision shall: (1) be made in ample time; (2) be large enough to be readily apparent to the other vessel; (3) be positive, timely, and seamanlike. A succession of small alterations is not sufficient. Course changes are preferred over speed reductions alone. If action results in a close-quarters situation, the vessel must slow, stop, or reverse as needed.
Exam tip
Rule 8 key principle: maneuvers must be large and obvious — not gradual. Small course changes that are not apparent to the other vessel do not satisfy Rule 8.
Rule 9 — Narrow Channels
Vessels shall keep to the starboard side of a narrow channel. A vessel less than 20 meters or a sailing vessel shall not impede a vessel that can safely navigate only within the channel. A vessel shall not cross a narrow channel if doing so impedes a vessel navigating within the channel. Vessels shall not anchor in a narrow channel if it can be avoided.
Exam tip
In a narrow channel: small vessels must NOT impede large vessels that can only navigate within the channel. The one-blast/two-blast passing signals are specifically for narrow channels (Inland Rule only).
Rule 10 — Traffic Separation Schemes
Vessels shall use TSS traffic lanes. In a lane, proceed in the direction of traffic flow. Crossing vessels shall cross on a heading as nearly as practicable at right angles. Vessels less than 20 meters and sailing vessels shall not impede vessels in a lane. A vessel may use the inshore zone. Fishing vessels shall not impede vessels using a lane.
Exam tip
The key crossing rule: when crossing a TSS lane, cross at right angles to the general traffic flow — regardless of whether that takes you across the bow of traffic.
Rule 11 — Application (Section II)
Section II rules (11–18) apply to vessels in sight of one another.
Rule 12 — Sailing Vessels
When two sailing vessels approach, the one on the PORT tack (wind from port side) gives way to the one on STARBOARD tack. When both on the same tack, the WINDWARD vessel gives way to the LEEWARD vessel. 'Windward' = the side from which the wind is blowing.
Exam tip
Port tack = give way. If you cannot determine the other vessel's tack when approaching at night, the vessel on port tack shall keep clear.
Rule 13 — Overtaking
An overtaking vessel is any vessel coming up from abaft the beam (more than 22.5° abaft the beam) of another vessel. The overtaking vessel shall keep out of the way of the vessel being overtaken. The overtaking obligation persists until the overtaking vessel is finally past and clear. This rule supersedes all other Rules 14–17 obligations.
Exam tip
The overtaking vessel is always the give-way vessel — even if it is a power vessel overtaking a sailing vessel. Rule 13 overrides Rules 12, 14, 15, 16, and 18.
Rule 14 — Head-on Situation
When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision, each shall alter course to STARBOARD and pass on the PORT side of the other. When in doubt — a head-on situation exists.
Exam tip
Head-on: both vessels alter to starboard. If doubt exists, the head-on situation is presumed. Important INLAND distinction: in a passing situation in a narrow channel, give one blast to propose passing on the port side of the other vessel (starboard-to-starboard) — the other vessel responds.
Rule 15 — Crossing Situation
When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her STARBOARD side shall keep out of the way. The give-way vessel shall avoid crossing ahead of the stand-on vessel.
Exam tip
Crossing rule: vessel with the other on her STARBOARD is give-way. If the other vessel is on YOUR starboard, YOU give way. Easy mnemonic: 'The vessel on the right has the right of way.'
Rule 16 — Action by Give-Way Vessel
The give-way vessel shall take early and substantial action to keep well clear.
Exam tip
Rule 16 specifies that give-way action must be EARLY and SUBSTANTIAL — not last-minute and marginal.
Rule 17 — Action by Stand-On Vessel
The stand-on vessel shall maintain course and speed. The stand-on vessel MAY take action as soon as it becomes apparent the give-way vessel is not taking appropriate action. The stand-on vessel SHALL take action (by itself, if necessary) when a collision cannot be avoided by the give-way vessel alone. A stand-on vessel altering course to PORT to avoid crossing traffic is prohibited unless the only option.
Exam tip
Rule 17 priority: (1) maintain course/speed; (2) may take action when give-way isn't acting; (3) MUST take action to avoid collision. The stand-on vessel cannot always shelter behind Rule 17 — it has a duty to act in extremis.
Rule 18 — Responsibilities Between Vessels
Hierarchy of right-of-way (highest to lowest — each must keep out of way of those above it): (1) Vessel not under command (NUC); (2) Vessel restricted in ability to maneuver (RAM); (3) Vessel constrained by draught (COLREGS only); (4) Vessel engaged in fishing; (5) Sailing vessel; (6) Power-driven vessel making way. Seaplanes and WIG craft have additional obligations.
Exam tip
Memorize the hierarchy top-to-bottom: NUC → RAM → CBD → Fishing → Sailing → Power. A power vessel must give way to ALL vessels above it. Note: CBD is COLREGS only — it does not exist in Inland Rules.
Rule 19 — Conduct in Restricted Visibility
Rule 19 applies when vessels are NOT in sight of one another. Every vessel shall proceed at a safe speed adapted to prevailing circumstances. A vessel shall have engines ready for immediate maneuver. On detecting another vessel by radar alone, a vessel shall determine if a close-quarters situation or collision risk will develop — if so, take avoiding action in ample time. Altering course to PORT for a vessel forward of the beam is prohibited unless the vessel is being overtaken. Altering course toward a vessel on the beam or abaft the beam is also prohibited.
Exam tip
Rule 19 critical exam point: in restricted visibility, do NOT alter course to PORT for a contact forward of the beam. Also: no sound signals on sight of a vessel — Rule 34 signals are for vessels in sight. In fog, use Rule 35 fog signals only.
Part C — Lights and Shapes
Rule 20 — Application
Lights required from sunset to sunrise and in restricted visibility. Shapes displayed during daylight hours only.
Rule 21 — Definitions
Masthead light: white, 225°, above and clear of hull. Sidelights: red (port, 112.5°) and green (starboard, 112.5°). Stern light: white, 135°. Towing light: yellow, 135° (same arc as sternlight). All-round light: 360°.
Exam tip
Sidelights: red = port (112.5°), green = starboard (112.5°). They cover together 225° forward. The memory aid: Port wine is red.
Rule 22 — Visibility of Lights
Required minimum visibility ranges: Masthead lights on vessels ≥50m = 6 miles. Sidelights on vessels ≥50m = 3 miles. Stern light on vessels ≥50m = 3 miles. Vessels 12–50m: masthead 5 miles, sidelights 2 miles, stern 2 miles. Vessels under 12m: all lights 2 miles (1 mile for sidelights under 7m in certain cases).
Exam tip
The exam often tests: what range must a masthead light be visible from a 100m vessel? Answer: 6 miles.
Rule 23 — Power-Driven Vessels Underway
Power-driven vessel underway: forward masthead light (white, 225°) + sidelights + sternlight. Vessels ≥50m: second (after) masthead light higher than forward. Vessels under 7m with max speed under 7 knots may show one all-round white light in lieu of full set.
Exam tip
The second masthead light on vessels ≥50m must be higher than the forward masthead light — a common exam diagram question.
Rule 24 — Towing and Pushing
Towing vessel (tow astern): two masthead lights (or three if tow length ≥200m), sidelights, stern light, and yellow towing light above sternlight. The tow shows sidelights and sternlight. Pushing: power vessel pushing ahead shows masthead lights (not towing), sidelights, and two yellow lights in vertical line at stern. A composite unit (rigidly connected) is treated as a power-driven vessel.
Exam tip
Length of tow ≥200m = THREE masthead lights on towing vessel, DIAMOND shape by day. Two masthead lights = tow under 200m.
Rule 25 — Sailing Vessels Underway and Vessels Under Oars
Sailing vessels: sidelights + sternlight. May also show red over green all-round lights at masthead (not a requirement). At night, a sailing vessel under 20m may combine sidelights into a tri-color lantern at masthead. Under oars: may show sailing vessel lights or just a white light.
Exam tip
Sailing vessel using engine + sails = power-driven vessel for rule purposes. The tri-color lantern replaces separate sidelights and stern light on vessels under 20m — not used simultaneously.
Rule 26 — Fishing Vessels
Vessel engaged in trawling: green over white all-round lights. Fishing (non-trawl): red over white all-round lights. A vessel fishing with nets extending >150m horizontally also shows an all-round white light in the direction of the nets. By day: basket shape (black). Fishing vessels underway also show sidelights and sternlight.
Exam tip
Memory aid: trawling = green (go) over white; fishing = red (stop) over white. The shape is a BASKET — not a ball or cone.
Rule 27 — Vessels Not Under Command and RAM
NUC: two red all-round lights (vertical) + if making way, sidelights and sternlight. By day: two balls. RAM: red-white-red all-round lights (vertical, ball-diamond-ball by day). Vessel engaged in dredging or underwater operations: on the obstructed side, two red all-round lights; on the passable side, two green all-round lights. A diver-down shape (rigid replica of flag) may be used.
Exam tip
NUC = two RED all-round. RAM = red-white-red. Day shapes: NUC = two balls; RAM = ball-diamond-ball. Dredging: two red = obstructed, two green = passable.
Rule 28 — Vessels Constrained by Draught (COLREGS Only)
CBD: three red all-round lights in a vertical line, or by day, a cylinder. CBD vessels navigate with very little water under the keel and cannot deviate course easily. COLREGS only — no inland equivalent.
Exam tip
CBD does not exist in Inland Rules. The shape is a CYLINDER. Three RED lights in a vertical line. Higher than a RAM vessel in the priority hierarchy.
Rule 29 — Pilot Vessels
A vessel engaged in pilotage duty: white over red all-round lights at the masthead; if underway, sidelights and sternlight; if at anchor, anchor light plus the white-over-red. By day, a flag with the letter 'H' (international code).
Exam tip
Pilot vessel = white over red (at top). Fishing = red over white. Do not confuse the order.
Rule 30 — Anchored Vessels and Vessels Aground
Anchored: one all-round white light forward. Vessels ≥50m: an additional all-round white light at the stern, lower than the forward. Vessels ≥100m must also illuminate decks. Aground: anchor lights plus two all-round red lights (vertical) or two balls by day.
Exam tip
Aground = anchor lights + TWO RED lights. Anchored = white light(s). Day shape: aground = two balls, anchored = one ball.
Rule 31 — Seaplanes and WIG Craft
Seaplanes and wing-in-ground (WIG) craft must comply as closely as possible with the light requirements for a vessel of their size and type.
Part D — Sound and Light Signals
Rule 32 — Definitions
Short blast: about 1 second. Prolonged blast: 4–6 seconds. These are the only two signal durations defined by the rules.
Exam tip
Short blast = 1 second. Prolonged blast = 4 to 6 seconds. Know the difference — exam questions often hinge on it.
Rule 33 — Equipment for Sound Signals
Vessels ≥12m must carry a whistle and bell. Vessels ≥100m must also carry a gong. The whistle must be audible at required distances based on vessel size. Vessels under 12m are not required to carry standard equipment but must be able to make an efficient sound signal.
Exam tip
Vessels ≥100m = whistle + bell + gong. Vessels 12–99m = whistle + bell. Under 12m = some means of making sound.
Rule 34 — Maneuvering and Warning Signals
For vessels IN SIGHT of each other: 1 short blast = I am altering course to starboard (COLREGS). 2 short blasts = I am altering course to port. 3 short blasts = I am operating astern propulsion. INLAND difference: 1 blast = I intend to leave you on my port side; 2 blasts = I intend to leave you on my starboard side. The other vessel must agree (give the same signal). 5 or more short blasts = doubt/danger signal.
Exam tip
This is the biggest COLREGS vs. Inland difference on the exam. COLREGS: signals describe action taken. Inland: signals are proposals requiring agreement. Both: 5+ blasts = danger.
Rule 35 — Sound Signals in Restricted Visibility
Power-driven vessel making way: one prolonged blast every 2 minutes. Power-driven vessel underway but stopped (no way): two prolonged blasts every 2 minutes. Sailing vessel, NUC, RAM, CBD, fishing vessel, or vessel being towed: one prolonged + two short blasts every 2 minutes. Towing vessel with tow: one prolonged + two short (same as restricted vessels). Vessel at anchor: bell for 5 seconds every 1 minute (vessels ≥100m also sound gong aft). Vessel aground: three distinct bell strokes + rapid ringing + three distinct strokes, every 1 minute.
Exam tip
Power-driven making way = ONE prolonged every 2 min. Stopped with no way = TWO prolonged every 2 min. Everything else (NUC, RAM, sailing, fishing, tow) = one prolonged + two short every 2 min. The anchor bell is every MINUTE, not 2 minutes.
Rule 36 — Signals to Attract Attention
A vessel may use any light or sound signal that cannot be mistaken for a signal authorized by the Rules. A vessel may also direct a spotlight toward a danger — in a manner that does not embarrass another vessel or mislead it.
Rule 37 — Distress Signals
Annex IV lists all authorized distress signals — signals indicating a vessel is in distress and requires assistance. They include: orange smoke, rocket with red stars, SOS by any means, MAYDAY on radio, NC signal flags, square flag with ball above or below, flames, parachute red flare, dye marker, EPIRBs, continuous fog signal, high-intensity white light flashing 50–70 times per minute.
Exam tip
Rule 37 does not list the signals — it refers to Annex IV. The exam may ask which Annex governs distress signals. Know at least 5 distress signals from Annex IV.
Part E — Exemptions
Rule 38 — Exemptions
Rule 38 provides for exemptions for vessels that could not comply with the light, shape, or sound equipment requirements due to age or construction. The rule sets a graduated compliance schedule based on vessel tonnage and age, allowing older vessels time to come into compliance. In practice, most vessels now in service post-date the exemption windows.
Exam tip
Rule 38 is rarely tested in depth. Know that it exists and relates to grandfathering older vessels that cannot comply with equipment requirements.
Lights and Shapes Quick Reference
| Vessel Type | Night Lights | Day Shape |
|---|---|---|
| Power-driven vessel (underway) | Masthead + sidelights + sternlight | None |
| Power-driven vessel ≥50m | Two masthead lights + sidelights + sternlight | None |
| Sailing vessel (underway) | Sidelights + sternlight | None |
| Vessel not under command (NUC) | Two red all-round (vertical) | Two balls |
| Vessel restricted in ability to maneuver (RAM) | Red-white-red all-round (vertical) | Ball-diamond-ball |
| Vessel constrained by draught (CBD, COLREGS only) | Three red all-round (vertical) | Cylinder |
| Trawling vessel | Green over white all-round + sidelights + sternlight | Two cones, apex together |
| Fishing (non-trawl) | Red over white all-round + sidelights + sternlight | Two cones, apex together |
| Towing (tow ≥200m) | Three masthead + sidelights + sternlight + yellow towing light | Diamond on tow |
| Towing (tow <200m) | Two masthead + sidelights + sternlight + yellow towing light | None |
| Pilot vessel (on duty) | White over red all-round at masthead | 'H' flag |
| Vessel at anchor (<50m) | One all-round white (forward) | One ball |
| Vessel at anchor (≥50m) | All-round white (forward) + all-round white (stern) | One ball |
| Vessel aground | Anchor lights + two red all-round (vertical) | Three balls (vertical) |
Sound Signal Quick Reference
COLREGS vs. Inland difference
Under COLREGS, maneuvering signals announce an action being taken. Under Inland Rules, they are proposals requiring the other vessel to respond with the same signal to indicate agreement. The danger signal (5+ short blasts) is the same in both.
| Signal | COLREGS Meaning | Inland Meaning |
|---|---|---|
| — (1 short) | Altering course to starboard | Proposal: pass port-to-port (agree with 1 short) |
| — — (2 short) | Altering course to port | Proposal: pass starboard-to-starboard (agree with 2 short) |
| — — — (3 short) | Operating astern propulsion | Operating astern propulsion |
| — — — — — (5+ short) | Doubt or danger | Doubt or danger |
| — (prolonged) | Power-driven vessel making way (fog, every 2 min) | Same |
| — — (2 prolonged) | Power vessel underway, no way (fog, every 2 min) | Same |
| — ∙ ∙ (prolonged + 2 short) | Sailing/NUC/RAM/CBD/fishing/tow (fog, every 2 min) | Same |
| Bell (5 sec) | Vessel at anchor (every 1 min) | Same |
Top 10 Exam Tips
COLREGS vs. Inland: The single most-tested area. Rule 34 maneuvering signals differ. Know both.
Hierarchy (Rule 18): NUC → RAM → CBD → Fishing → Sailing → Power. CBD is COLREGS-only.
Overtaking (Rule 13): Always the give-way vessel, no exceptions. Overrides Rules 12, 14, 15.
Rule 19 (fog): Do not alter course to PORT for a contact FORWARD of the beam.
Lights test: Know the arcs — masthead 225°, sidelights 112.5° each, sternlight 135°.
CBD shape: cylinder (not a ball or diamond). Three red all-round lights at night.
Anchor vs. aground: Aground = anchor lights + two red all-round. Day: aground = three balls.
Towing: Two masthead lights = tow under 200m. Three masthead lights = tow 200m or over.
Fog signals: Power making way = 1 prolonged/2 min. Stopped = 2 prolonged/2 min. All others = 1 prolonged + 2 short/2 min.
Rule 5 (lookout): Required at ALL times, all conditions — radar alone is not sufficient.