The COLREGs are the traffic laws of the sea. Formally titled the International Regulations for Preventing Collisions at Sea, 1972, they set out the navigation rules that every vessel follows to avoid running into another vessel. Whether you skipper a 40 foot sailboat on a weekend, run a superyacht across the Atlantic, or stand a bridge watch as professional crew, the same core logic applies: know who gives way, know who stands on, keep a proper lookout, use a safe speed, and understand what the lights and shapes on another vessel are telling you. This guide walks through the rules of the road boating candidates and working mariners actually need, from the give way vs stand on decision to the full set of COLREGs lights, and it explains how the International Regulations differ from the US Inland Rules.
Learning these rules is not about memorizing trivia. It is about building a mental model so that when you see a green light low on the horizon at 0200, or hear one prolonged blast in fog, your hands already know what to do. Below you will find the steering and sailing rules, the pecking order of responsibilities between vessels, the sound and light signals, the lights and shapes reference, restricted visibility procedures, and study advice for the USCG, RYA, and STCW exams. Along the way there are practical notes for both recreational boaters and career crew.
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Build a free crew profileCOLREGs stands for the Collision Regulations. They were agreed under the International Maritime Organization and came into force in 1977, replacing an older 1960 set. The full document is organized into parts and rules, numbered 1 through 38, followed by four annexes and a set of interpretive appendices. When people talk about "the navigation rules," they usually mean this book, or its national equivalent. In the United States, the Coast Guard publishes a combined volume that places the International Rules alongside the US Inland Rules, so a mariner can compare them side by side.
Here is the key distinction that trips up new students. The International Rules apply on the high seas and in most coastal waters seaward of a demarcation line. The US Inland Rules apply landward of that COLREGs Demarcation Line, which runs across the entrances of bays, rivers, and harbors and is printed on nautical charts. Most of the two rulebooks are identical word for word. The differences are concentrated in a handful of areas: certain sound signals, some light and shape requirements, and the specific wording around narrow channels and traffic in rivers. A professional who works both offshore and inland has to hold both versions in mind and know which one governs at a given position.
The rules are grouped logically. Part A covers general matters, application, responsibility, and definitions. Part B, the largest and most examined section, contains the steering and sailing rules and splits into conduct in any visibility, conduct of vessels in sight of one another, and conduct in restricted visibility. Part C covers lights and shapes. Part D covers sound and light signals. Part E covers exemptions, and Part F, added later, covers verification of compliance. If you learn the structure, finding a rule under pressure becomes far easier.
Before any specific maneuver, Rule 2 sets the tone. It says that nothing in the rules exempts any vessel, or her owner, master, or crew, from the consequences of neglect. It also contains what mariners call the general prudential rule: in special circumstances, including the limitations of the vessels involved, a departure from the rules may be necessary to avoid immediate danger. In plain terms, the rules are not a suicide pact. If following a rule to the letter would cause a collision, you are required to do whatever avoids the collision. Examiners love Rule 2 because it shows whether a candidate understands that good seamanship overrides mechanical rule-following.
Two rules do more work than any others, and both are frequently cited in collision investigations. Rule 5 requires every vessel to maintain a proper lookout by sight and hearing, as well as by all available means appropriate to the prevailing circumstances, so as to make a full appraisal of the situation and of the risk of collision. "All available means" includes radar, AIS, and simply listening. A lookout is not only the person on the bow. It is a continuous duty of the watch. Many casualties come down to a lookout failure: a phone in hand, an unmanned wheelhouse, a single crew member trying to plot, steer, and watch all at once.
Rule 6 requires a safe speed at all times, so that the vessel can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances. The rule lists factors to weigh: visibility, traffic density, the vessel's stopping distance and maneuverability, background lights at night, the state of wind and sea, and the draught relative to the available depth. Vessels with radar get an additional list of factors. Note that "safe speed" is not a fixed number. Ten knots may be reckless in fog near a fairway and perfectly safe on open water in clear daylight. The exam answer is always situational.
Rule 7 tells you how to decide whether a risk of collision exists. Use all available means appropriate to the conditions. If you have radar, use it properly, including long-range scanning and plotting or equivalent systematic observation. The classic test: if the compass bearing of an approaching vessel does not appreciably change, a risk of collision exists. This constant bearing, decreasing range situation is the heart of the matter. Watch the bearing. If it holds steady while the range closes, you are on a collision course, even with a vessel that seems to be passing "off to the side." Rule 7 also warns against making assumptions on scanty information, especially scanty radar information.
Rule 8 governs action to avoid collision. Any action must be positive, made in ample time, and with due regard to good seamanship. A change of course or speed should be large enough to be readily apparent to another vessel visually or by radar. A succession of small alterations is discouraged because it confuses the other party. If there is enough sea room, a course alteration alone may be the most effective action, provided it is made in good time and does not create a close-quarters situation with a third vessel. Rule 8 also introduces the idea that a vessel required to keep out of the way must, so far as possible, take early and substantial action to keep well clear.
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Find boating courses and services freeWhen two power-driven vessels meet in sight of one another, one is the give-way vessel and the other is the stand-on vessel. This is the single most important concept in the rules of the road boating exam and on the water. The give-way vessel must take early and substantial action to keep clear, under Rule 16. The stand-on vessel, under Rule 17, must initially keep her course and speed so that the give-way vessel can predict what she will do. Predictability is the whole point. If both vessels start maneuvering unpredictably, the system breaks down.
But the stand-on role is not a license to hold course into a collision. Rule 17 has stages. Initially the stand-on vessel keeps course and speed. As soon as it becomes apparent that the give-way vessel is not taking appropriate action, the stand-on vessel may take action by her maneuver alone. And when collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel must take whatever action will best avoid collision. Crucially, if the stand-on vessel is a power-driven vessel taking action in a crossing situation, she should, if the circumstances allow, not alter course to port for a vessel on her own port side. Understanding the give way vs stand on staging separates a competent watchkeeper from a rote memorizer.
Three specific geometries cover most power-driven encounters, and each has a defined answer.
Overtaking, Rule 13. A vessel is overtaking when she approaches another from more than 22.5 degrees abaft that vessel's beam, meaning she can see only the sternlight of the vessel ahead and neither sidelight. The overtaking vessel is always the give-way vessel and must keep clear until she is finally past and clear. This duty does not change even if the overtaking vessel is a sailing vessel and the vessel ahead is under power. Rule 13 overrides the sailing rules. If in doubt whether you are overtaking, assume you are and act accordingly.
Head-on, Rule 14. When two power-driven vessels meet on reciprocal or nearly reciprocal courses so as to involve risk of collision, each alters course to starboard so that each passes on the port side of the other. In other words, both turn right and pass port to port, like cars on a two-lane road in a right-hand-drive country. At night you know you are head-on when you see both sidelights of the other vessel, red and green together, and her masthead lights in a line. If in doubt whether a head-on situation exists, assume it does and turn to starboard.
Crossing, Rule 15. When two power-driven vessels are crossing so as to involve risk of collision, the vessel that has the other on her own starboard side must keep out of the way. A memory aid: if the other vessel is on your right and you see her red port sidelight facing you, you give way, because red means stop. If the other vessel is on your left showing you her green starboard light, you stand on, because green means go. The give-way vessel should, if circumstances allow, avoid crossing ahead of the other vessel. Slowing, stopping, or altering course to pass astern are all acceptable, and passing astern is usually the cleanest solution.
Not all vessels are equal in maneuverability, so the rules establish a hierarchy of who gives way to whom. Rule 18 sets out this pecking order for vessels in sight of one another. The general principle: the more constrained a vessel is in her ability to maneuver, the more the burden of keeping clear falls on others. A power-driven vessel that can turn on a dime must keep clear of a large ship that is restricted in her ability to alter course. The table below shows the order, with the least maneuverable at the top.
| Priority (top = others give way) | Vessel type | Give way to whom? |
|---|---|---|
| 1 (highest) | Vessel not under command (NUC) | No one; others keep clear of her |
| 2 | Vessel restricted in her ability to maneuver (RAM) | NUC only |
| 3 | Vessel constrained by her draught (International only) | NUC and RAM |
| 4 | Vessel engaged in fishing | The three above |
| 5 | Sailing vessel | All the above |
| 6 | Power-driven vessel | Everyone above her |
| 7 (special) | Seaplane / WIG craft | Keep well clear of all vessels |
A common mnemonic runs "New Reels Catch Fish So Purely" or the older "Nobody Really Cares For Sailors Preferences," mapping to Not under command, Restricted, Constrained by draught, Fishing, Sailing, Power. Learn one that sticks. Note the important caveats: a seaplane on the water generally keeps well clear of all vessels and avoids impeding their navigation. A vessel constrained by draught appears only in the International Rules, not the US Inland Rules, and even NUC and RAM vessels must not, under Rule 8, embarrass another vessel through careless action. The hierarchy governs who gives way, but it never removes the universal duty to avoid collision.
Rule 9 covers narrow channels. Keep to the starboard side of a fairway or channel that is safe and practicable. A vessel under 20 meters, a sailing vessel, or a vessel engaged in fishing must not impede a vessel that can safely proceed only within the channel. Do not cross a narrow channel if doing so impedes a vessel confined to it. Rule 10 covers traffic separation schemes, the marine equivalent of divided highways at busy approaches. Proceed in the correct lane, in the general direction of traffic flow, join and leave at the ends where practicable, and cross lanes at as close to a right angle to the flow as you can manage. These rules matter enormously to professional crew who work the approaches to Rotterdam, the Solent, Singapore Strait, or Miami.
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Build a free crew profileWhen two sailing vessels approach one another with risk of collision, three tests decide who keeps clear. First, when each has the wind on a different side, the vessel with the wind on her port side keeps out of the way. Second, when both have the wind on the same side, the vessel to windward keeps out of the way of the vessel to leeward. Third, if a vessel with the wind on her port side sees a vessel to windward and cannot tell whether the other has the wind to port or starboard, she keeps out of the way. The windward side is the side opposite to that on which the mainsail is carried. Remember that the moment either sailing vessel starts her engine, she becomes a power-driven vessel and the sailing rules no longer apply between them.
Lights are the language of the sea after dark. By reading the pattern, arc, and color of another vessel's lights, you can identify her type, her heading relative to you, roughly her size, and what she is doing, all before you can see her hull. Learning COLREGs lights well is what lets a watchkeeper turn a scatter of dots on a dark horizon into a clear picture. Here are the building blocks defined in Rule 21.
Notice that a masthead light's 225 degrees plus a sternlight's 135 degrees add to a full 360 degree circle, and the sidelights each match their half of the masthead arc. That geometry is deliberate. It means the color you see tells you your aspect on the other vessel: both sidelights and masthead lights means head-on or nearly so; a single sidelight with a masthead light means a crossing aspect; a white sternlight alone means you are astern and overtaking.
The table below is a study aid, not a substitute for the rule book, but it captures the configurations that come up most often on exams and on watch. "Shapes" are the daytime black shapes that convey the same status a light does at night, defined in Rule 20 and shown from sunrise to sunset.
| Vessel / situation | Lights at night | Day shape |
|---|---|---|
| Power-driven vessel underway | Masthead light(s), sidelights, sternlight | None |
| Sailing vessel underway | Sidelights and sternlight (no masthead light) | None (a cone point-down if also motoring) |
| Vessel under sail and power (motorsailing) | Sidelights, sternlight, and masthead light (treated as power-driven) | One black cone, point down |
| Vessel at anchor | All-round white light(s); 50 m or more shows two, fore and aft | One black ball forward |
| Vessel aground | Anchor light(s) plus two all-round red lights in a vertical line | Three black balls in a vertical line |
| Vessel not under command (NUC) | Two all-round red lights in a vertical line | Two black balls in a vertical line |
| Restricted in ability to maneuver (RAM) | Red, white, red all-round in a vertical line | Ball, diamond, ball in a vertical line |
| Constrained by draught (International) | Three all-round red lights in a vertical line (plus normal lights) | Black cylinder |
| Vessel engaged in fishing (trawling) | Green over white all-round lights | Two cones point to point (hourglass) |
| Vessel fishing, not trawling | Red over white all-round lights | Two cones point to point (hourglass) |
| Pilot vessel on duty | White over red all-round lights ("white over red, pilot ahead") | None |
| Vessel towing (tow over 200 m) | Three masthead lights in a line, sidelights, sternlight, yellow towing light | Black diamond on tow and towed vessel |
Two memory hooks worth keeping: "red over red, the captain is dead" reminds you that two red all-round lights mean not under command. "White over red, pilot ahead" and "red over white, fishing at night" round out the set. These little rhymes have saved many watchkeepers a moment of doubt at the worst possible time. For a broader primer aimed at newcomers, our guide on how to drive a boat pairs well with this lights section.
Rules 32 through 34 cover sound signals. A short blast lasts about one second. A prolonged blast lasts four to six seconds. In sight of one another, a power-driven vessel that is altering course announces the maneuver with her whistle. The signals differ between International and Inland rules, and this is one of the areas where the two rulebooks genuinely diverge, so learn both.
The key Inland versus International difference: Inland uses "signals of intent," where one blast proposes a port-to-port passing and the other vessel agrees or sounds the danger signal. International uses "signals of action," describing what you are doing at that moment. Confusing the two on an exam is a classic mistake. In practice, five short blasts is the single most useful signal for a recreational boater to know, because it is the universal "wake up, I do not trust what you are doing" call.
In or near an area of restricted visibility, day or night, different signals apply, sounded at intervals of not more than two minutes:
Rule 19 stands apart because it applies to vessels that are not in sight of one another when in or near restricted visibility. Fog changes everything. There is no stand-on vessel in fog. Both vessels have obligations. Every vessel must proceed at a safe speed adapted to the conditions and a power-driven vessel must have engines ready for immediate maneuver. When a vessel detects by radar alone the presence of another vessel, she determines whether a close-quarters situation is developing or a risk of collision exists, and if so takes avoiding action in ample time.
Rule 19 then gives two specific prohibitions for that radar-only avoiding action. Avoid an alteration of course to port for a vessel forward of the beam, unless that vessel is being overtaken. And avoid an alteration of course toward a vessel abeam or abaft the beam. In simpler terms, when you pick up a target on radar in fog, favor a turn to starboard for something ahead, and do not turn toward something beside or behind you. Finally, if a vessel hears the fog signal of another apparently forward of her beam, or cannot avoid a close-quarters situation with a vessel forward of the beam, she must reduce to bare steerageway and, if necessary, take all way off, then proceed with extreme caution until the danger is over. Fog demands slow speed, sharp listening, and disciplined radar work above all else.
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Find boating courses and services freeImagine you are on a power-driven vessel at night in open water. Ahead and to your right you pick up a light. As it develops you see a red sidelight and a masthead light, no green. The vessel is showing you her port side, crossing from your starboard to your port. You check the bearing over several minutes: it holds nearly steady while the range closes. That is risk of collision under Rule 7. Under Rule 15, because she is on your starboard side, you are the give-way vessel. Under Rule 16 you take early and substantial action. You alter boldly to starboard, passing well astern of her, a change large enough that her watchkeeper sees your aspect open up on radar and by eye. You do not cross ahead. Once past and clear, you resume your course. Meanwhile she, as the stand-on vessel under Rule 17, holds her course and speed so you can predict her, ready to act herself if you fail to. That single scenario exercises half a dozen rules at once, which is exactly why examiners build questions around it.
COLREGs knowledge sits at the center of nearly every deck qualification. Professional and recreational tracks differ in format but test the same rules.
USCG. United States Coast Guard license exams, from OUPV (six-pack) up through Master and Mate of larger tonnage, include a dedicated Rules of the Road module. Candidates must typically score 90 percent on the Rules section, higher than the passing mark for other modules, because a rules error at sea can be fatal. The questions draw on both International and Inland rules, including light and shape identification and the exact wording of numbered rules. Many candidates drill with question banks and light-recognition flashcards until the answers are automatic.
RYA. The Royal Yachting Association threads the IRPCS (the RYA's term for the COLREGs) through its whole scheme, from Day Skipper theory up to Yachtmaster Offshore and Ocean. The Yachtmaster practical exam includes night navigation where an examiner will point at lights on the water and expect an instant, correct identification, along with the right give-way action. Our Yachtmaster and RYA certification guide lays out the full pathway and what each level demands.
STCW. The Standards of Training, Certification and Watchkeeping convention governs professional seafarers worldwide. Officer of the Watch candidates study the COLREGs in depth as part of navigation and watchkeeping competence, and demonstrate them in oral exams and on simulators. For anyone building a career at sea, solid COLREGs command is not optional; it is the baseline every officer is measured against.
For recreational boaters in the US, the state boating-safety courses cover a simplified but accurate version of the same rules. Our boating license and boater safety course guide explains which certificate you need and where to earn it. Whatever your track, the study method that works best is the same: understand the logic first, then drill the specifics, then practice reading real lights and real geometry until recognition is instant.
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Build a free crew profileA few errors recur again and again. Turning to port in a crossing situation to "duck behind" a vessel on your starboard side, which the rules specifically discourage because it puts you across her bow. Making a series of small course changes instead of one bold, obvious alteration, leaving the other vessel unable to read your intent. Treating the stand-on role as an absolute right and holding course into danger rather than acting when it becomes clear the give-way vessel will not. Forgetting that the overtaking rule outranks the sailing rules, so a sailing vessel overtaking a powerboat still gives way. Assuming there is a stand-on vessel in fog when Rule 19 says there is not. And relying on scanty radar information to make an assumption, which Rule 7 explicitly warns against. Knowing where these traps sit is half the battle.
Most of the two rulebooks match, so focus your effort on the divergences. The whistle signals differ: Inland uses signals of intent (one blast proposes leaving the other to port), International uses signals of action (one blast means altering to starboard now). The vessel constrained by her draught, with its three vertical red lights, exists only in the International rules. Inland has specific provisions for vessels operating on the Great Lakes and Western Rivers, and a slightly different treatment of narrow-channel signaling and the special downbound-vessel priority on Western Rivers. Inland also allows certain vessels to display a flashing yellow or other special lights not found in the International set. When you cross the COLREGS Demarcation Line printed on your chart, the governing rulebook changes, and a professional watchkeeper tracks that boundary as carefully as any other navigational hazard.
They describe the same thing from different angles. "COLREGs" is the informal name for the International Regulations for Preventing Collisions at Sea, 1972. "Navigation Rules" is the broader term used, especially in the United States, for the published combination of the International Rules and the US Inland Rules. In everyday use, a mariner saying "the rules of the road" means whichever set governs the water they are on.
Look at the other vessel's sidelight or her position. If she is on your starboard (right) side, or you see her red port light facing you, you give way, and red means stop. If she is on your port (left) side, or you see her green starboard light, you stand on, and green means go. The give-way vessel takes early, obvious action, usually altering to starboard to pass astern. The stand-on vessel holds course and speed but must still act if collision looms.
Two all-round red lights in a vertical line mean the vessel is not under command, unable to maneuver as required, perhaps from an engine or steering failure. The memory aid is "red over red, the captain is dead." Every other vessel must keep clear of her. By day the same status is shown by two black balls in a vertical line.
Five or more short and rapid blasts is the danger or doubt signal. It means "I do not understand your intentions" or "I doubt you are taking enough action to avoid a collision." Any vessel that is unsure of another's intentions may and should sound it. For recreational boaters it is the most important sound signal to know and to recognize.
No. Rule 19, which covers conduct in restricted visibility for vessels not in sight of one another, does not designate a stand-on vessel. Both vessels have a duty to take avoiding action. You proceed at a safe speed, keep engines ready, and if you detect a vessel by radar alone, take early action, favoring a turn to starboard for a target ahead and avoiding a turn toward a target abeam or behind.
No, and "right of way" is not really the correct phrase. Under Rule 18, a power-driven vessel generally keeps clear of a sailing vessel, but there are big exceptions. A sailing vessel that is overtaking a powerboat must keep clear, because the overtaking rule overrides everything else. A sailing vessel must also keep clear of a vessel not under command, one restricted in her ability to maneuver, one constrained by draught, or one engaged in fishing. And in a narrow channel a sailing vessel must not impede a vessel that can only proceed within that channel. No vessel ever has an absolute right to stand into a collision.
USCG license exams require about 90 percent on the Rules of the Road section, a higher bar than other modules. RYA Day Skipper and Yachtmaster exams test the IRPCS in theory and in live night-navigation practicals. STCW Officer of the Watch certification tests them in orals and simulators. The rules are the same; the depth and format scale with the license. Consistent drilling of rule wording, light recognition, and geometry is the path through all of them.
The COLREGs reward study because they are logical. Once you see that every rule serves one goal, preventing collisions, the numbered clauses stop feeling like a list to memorize and start feeling like common sense written down carefully. Keep a copy aboard, review the lights until you can name them at a glance, and practice the give-way decision every time you are on the water until it becomes second nature. Whether you are a boater refreshing before the season or professional crew preparing for a ticket, the effort pays off in confidence and in safety.
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