COLREGS Rules of the Road — Complete Exam Reference
International Regulations for Preventing Collisions at Sea — all 38 rules, 4 annexes, Rule 18 hierarchy, encounter situations, Inland differences, and the exam memory aids that stick. Built for the USCG OUPV and Master captain's license exam.
COLREGS Structure: 5 Parts, 38 Rules, 4 Annexes
The International Regulations for Preventing Collisions at Sea (COLREGS) are organized into five parts. The U.S. Inland Rules follow the same structure and most rules are identical — the key differences are in Part B (steering and sailing rules) and Part D (sound signals).
The Four Annexes
Exact positioning requirements for navigation lights: heights, separation distances between lights, visibility requirements. Defines minimum luminosity. Specifies screen requirements for sidelights.
Additional light and shape signals used by fishing vessels when operating near other fishing vessels. Includes signals for pair trawling, purse seiners, and gear direction indicators.
Specifications for whistles, bells, and gongs: frequency ranges, sound pressure levels, operating ranges. Defines short blast (1 second) and prolonged blast (4 to 6 seconds).
Lists 15 recognized distress signals including: red parachute or hand flare, orange smoke, SOS by any signaling method, MAYDAY on radiotelephone, raising and lowering outstretched arms, continuous sounding of fog signal, flames on a vessel, dye marker, square flag plus ball, EPIRB signals.
Rule 3 — Key Definitions
Rule 3 definitions are frequently tested. The exam distinguishes between vessel types that look similar but have different privileges. Memorize these precisely.
| Term | Definition |
|---|---|
| Vessel | Every description of water craft including non-displacement craft, WIG craft, and seaplanes used or capable of being used as a means of transportation on water. |
| Power-driven vessel | Any vessel propelled by machinery — including a sailing vessel with its engine running. |
| Sailing vessel | Any vessel under sail, provided that propelling machinery is not being used. If engine is on, it is power-driven. |
| Vessel not under command (NUC) | A vessel which through some exceptional circumstance is unable to maneuver as required and is therefore unable to keep out of the way of another vessel. |
| Restricted in ability to maneuver (RAM) | A vessel restricted by the nature of her work from maneuvering as required, including cable-laying, dredging, replenishment at sea, aircraft operations, mine clearance, towing. |
| Constrained by draft (CBD) | A power-driven vessel which, because of her draft in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following. International Rules only. |
| Vessel engaged in fishing | Any vessel fishing with nets, lines, trawls, or other fishing apparatus which restricts maneuverability. Does NOT include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability. |
| Seaplane | Any aircraft designed to maneuver on the water. |
| WIG craft | A multimodal craft which, in its main operational mode, flies in close proximity to the surface by utilizing surface-effect action. |
Rule 18 — Responsibility Hierarchy Between Vessels
Rule 18 is the most-tested rule on the USCG exam. Every vessel must give way to all vessel types ranked above it. The lower a vessel sits in the hierarchy, the more give-way obligations it carries. Memory aid: Never Refuse Cold Fish Sandwiches Please (NUC, RAM, CBD, Fishing, Sail, Power).
| Rank | Vessel Type |
|---|---|
| 1 | Not Under Command (NUC) Two all-around red lights (vertically) |
| 2 | Restricted in Ability to Maneuver (RAM) Red, white, red all-around lights (vertically) |
| 3 | Constrained by Draft (CBD) Three all-around red lights (vertically) |
| 4 | Engaged in Fishing or Trawling Green over white (trawling) or red over white (other fishing) + sidelights when making way |
| 5 | Under Sail Sidelights + stern light (tricolor optional on vessels under 20m) |
| 6 | Power-Driven Underway Masthead light + sidelights + stern light |
| 7 | Seaplane As far as practicable, conform to power-driven vessel lights |
Encounter Situations — Head-On, Crossing, Overtaking
These three situations (Rules 13, 14, 15) are the core of the Rules of the Road exam. Understand when each applies and exactly which vessel must act.
Head-On (Rule 14)
Both vessels meeting approximately end-on or nearly end-on
BOTH alter course to starboard — pass port-to-port
International: 1 short each. Inland: 1 short, wait for agreement.
Head-on — both go right (starboard)
Crossing (Rule 15)
Vessels approaching so as to involve risk of collision at an angle
Vessel with the other on its STARBOARD side is give-way
International: 1 short (altering to starboard). Inland: 1 short for intent.
Starboard side = give way. The other vessel is on your right? You yield.
Overtaking (Rule 13)
Coming from more than 22.5 degrees abaft the other vessel's beam (in the overtaking cone)
Overtaking vessel ALWAYS keeps clear regardless of other rules
Inland: 1 long + 1 short (starboard pass) or 1 long + 2 short (port pass), agree before passing. International: 2 long + 1 short (starboard) or 2 long + 2 short (port).
Once an overtaking vessel, always give-way until safely past and clear.
Give-Way vs. Stand-On Quick Reference
| Rule | Give-Way Vessel | Stand-On Vessel |
|---|---|---|
| Rule 13 — Overtaking | Overtaking vessel | Vessel being overtaken |
| Rule 14 — Head-on | Both vessels | Both vessels |
| Rule 15 — Crossing | Vessel with other on its STARBOARD side | Vessel with other on its PORT side |
| Rule 16 — Give-Way Duty | Must take early and substantial action to keep well clear | — |
| Rule 17 — Stand-On Duty | — | Maintain course and speed; may act if give-way fails; must act if imminent |
| Rule 18 — Hierarchy | Power (rank 6), Sailing (rank 5), Fishing (rank 4) | NUC (rank 1), RAM (rank 2), CBD (rank 3, international) |
All Key Rules — Detailed Reference
Every vessel must comply with the rules but must also take any action required by ordinary practice of seamen or special circumstances. The rules are a floor — good seamanship can require more. A vessel may depart from the rules to avoid immediate danger.
Defines: vessel (includes WIG craft and seaplanes), power-driven vessel (using machinery for propulsion), sailing vessel (under sail only — not engine), vessel not under command (NUC — exceptional circumstance), RAM (restricted by nature of work), CBD (constrained by draft), vessel engaged in fishing (gear that restricts maneuverability — NOT trolling or sport fishing), seaplane.
Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision. There are no exceptions — the lookout duty is absolute and continuous.
Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. Factors include visibility, traffic density, maneuverability, wind/sea/current, proximity of hazards, draft versus available depth, and radar limitations.
Every vessel shall use all available means to determine if risk of collision exists. If in doubt, assume risk exists. A compass bearing (relative or true) that does not change as range decreases indicates collision risk. Radar is required if fitted. A vessel shall not assume risk is absent merely because no risk was initially detected.
Action must be: (1) taken in ample time, (2) positive, (3) large enough to be readily apparent to the other vessel. Do not make a series of small alterations. If sea room allows, alteration of course alone is preferred. Avoid crossing ahead of the stand-on vessel. Reduce speed if needed; stop if necessary.
Vessels shall keep as far to the starboard side of a narrow channel or fairway as is safe and practicable. Vessels of less than 20 meters or sailing vessels shall not impede vessels that can navigate only inside a narrow channel. Overtaking in narrow channels requires agreement signal under Inland Rules. Crossing vessels must not impede vessels following the channel. Anchoring in channels is prohibited where possible.
Vessels using a TSS shall proceed in the appropriate traffic lane in the general direction of traffic flow for that lane. Entry and exit shall be made at small angles to the general traffic flow. Vessels shall avoid crossing traffic lanes if possible; if necessary, cross at right angles to the traffic flow. Fishing vessels shall not impede a vessel following a traffic lane. TSS do not relieve vessels of their duty under the rules.
When two sailing vessels approach so as to involve risk of collision: (1) if on opposite tacks, the vessel on the port tack gives way; (2) if on the same tack, the windward vessel gives way; (3) a vessel on port tack that cannot determine the tack of the other vessel shall keep clear. Windward is defined as the side opposite to the main sail.
Any vessel overtaking shall keep out of the way of the vessel being overtaken. A vessel is overtaking when coming up from a direction more than 22.5 degrees abaft the beam of another vessel — that is, within the stern light arc. Once classified as overtaking, that designation persists until the vessel is finally past and clear, regardless of subsequent bearing changes.
When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision, each shall alter her course to starboard so that each shall pass on the port side of the other. When in doubt whether a head-on situation exists, it shall be deemed to exist. The rule applies when the other vessel is seen directly ahead or nearly ahead.
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 and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.
Every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear. The give-way vessel has the first obligation and the best opportunity to avoid collision.
The stand-on vessel shall maintain its course and speed. It may take action to avoid collision by its maneuver alone as soon as it becomes apparent the give-way vessel is not taking appropriate action. When collision cannot be avoided by the give-way vessel alone, the stand-on vessel MUST take action. The stand-on vessel shall not alter course to port for a vessel on its own port side.
Establishes the right-of-way hierarchy. A power-driven vessel underway shall keep out of the way of: NUC, RAM, fishing, and sailing vessels. A sailing vessel underway shall keep out of the way of: NUC, RAM, and fishing vessels. A vessel engaged in fishing shall keep out of the way of: NUC and RAM. A vessel NUC or RAM shall give way to CBD (international only). Seaplanes shall keep clear of all vessels.
Applies when vessels are NOT in sight of each other. Rules 13-17 do NOT apply. Every vessel must: proceed at safe speed, have engines ready for immediate maneuver, use radar if fitted, avoid close-quarters situations. If a fog signal is heard forward of the beam, reduce to minimum speed. Any vessel may stop engines to listen. There is no give-way or stand-on in restricted visibility.
Inland Rules vs. International COLREGS — Key Differences
International COLREGS apply on the high seas and international waters. U.S. Inland Rules apply inside the demarcation lines — harbors, inland waters, rivers. The exam tests both, with special emphasis on sound signal differences and the CBD distinction.
Sound 1 prolonged plus 1 short blast (starboard) or 1 prolonged plus 2 short blasts (port). WAIT for agreement signal from the vessel being overtaken. If the overtaken vessel disagrees, it sounds 5 short blasts.
Sound 2 long plus 1 short (starboard) or 2 long plus 2 short (port). No agreement required — this is an intent signal only.
1 short = I intend to leave you on my port side. 2 short = I intend to leave you on my starboard side. Must wait for agreement before altering course.
1 short = I am altering course to starboard. 2 short = I am altering course to port. Signals describe action already taken or about to be taken — no agreement needed.
Not a recognized privileged class. A vessel constrained by draft gets NO special right-of-way under Inland Rules.
Rule 28 recognizes CBD vessels. They display 3 all-around red vertical lights and a cylinder day shape. Power-driven vessels must give way.
Agreement signals required (1 long + 1 short or 1 long + 2 short, then match from overtaken vessel). 5 short if no agreement.
No mandatory agreement signal required. Overtaking vessel still keeps clear per Rule 13.
On designated Western Rivers: downstream vessel has right of way over upstream vessel in a meeting situation. Crossing vessel always gives way to vessel following the channel, regardless of which side the other is on.
No Western Rivers equivalent. International Rules apply on high seas only.
A vessel may use a flashing light (1 flash = starboard, 2 flashes = port) to supplement or replace whistle signals in certain circumstances.
No equivalent flashing light maneuver signal. Whistle signals are used exclusively.
Vessels under 50 meters at anchor may exhibit one all-around white light forward at a height visible all around. Specific minimum heights may differ.
Same general rule but specific height requirements and vessel length thresholds differ slightly.
Rule 9 and Rule 10 — Narrow Channels and Traffic Separation
Rule 9 — Narrow Channels
- 1. Keep to the starboard side of a narrow channel or fairway as far as safe and practicable.
- 2. Vessels under 20 meters and sailing vessels shall NOT impede vessels that can navigate only inside the channel.
- 3. Fishing vessels shall NOT impede vessels navigating the channel.
- 4. Crossing vessels shall NOT impede vessels following the channel — but Rule 15 still applies when the situation is a genuine crossing with risk of collision.
- 5. Overtaking in a narrow channel: under Inland Rules, mandatory agreement signals required. Under International Rules, overtaker still keeps clear.
- 6. Sound signal at a blind bend: 1 prolonged blast. Answer with 1 prolonged if approaching from the other direction.
Rule 10 — Traffic Separation Schemes
- 1. Use the correct traffic lane. Proceed in the general direction of traffic flow.
- 2. Enter and exit traffic lanes at a SMALL angle to the general traffic flow (nearly parallel).
- 3. If you must CROSS a TSS, do so at right angles (90 degrees) to the traffic flow.
- 4. Vessels under 20 meters and sailing vessels shall NOT impede vessels in a lane.
- 5. Fishing vessels shall NOT impede vessels following a lane.
- 6. Vessels less than 20 meters or engaged in fishing may use inshore traffic zones. Vessels joining a lane from the inshore zone do so at low angle.
Rule 12 — Sailing Vessel Encounters
Rule 12 applies only when BOTH vessels are under sail. If one vessel is power-driven, Rule 18 applies (sailing vessel has privilege over power). The three scenarios under Rule 12:
The vessel on the port tack gives way to the vessel on the starboard tack.
The vessel to windward (upwind) gives way to the vessel to leeward (downwind).
A vessel on the port tack that cannot determine the other vessel's tack must keep clear.
Exam Memory Aids
These mnemonics and memory shortcuts are tested repeatedly on the USCG exam. Drill them until they are automatic.
NUC, RAM, CBD (international only), Fishing, Sailing, Power. Each gives way to all above it.
Head-on: both alter to starboard. Crossing: vessel with other on starboard gives way. Overtaking: overtaker always keeps clear.
Masthead (225 degrees) plus stern (135 degrees) covers full circle. Two sidelights (112.5 each) equal the masthead arc forward.
When vessels cannot see each other due to fog or reduced visibility, the crossing/head-on/overtaking rules are suspended. Everyone uses caution.
The stern light covers 135 degrees centered on dead astern. If you can see the other vessel's stern light, you are in the overtaking zone and must keep clear.
A vessel constrained by draft gets special right-of-way under International COLREGS (Rule 28) but NONE under U.S. Inland Rules. This is a common exam trap.
Give-way action must be taken in ample time, must be large enough to be apparent, must be positive (not small increments). Avoid crossing ahead of the stand-on vessel.
Opposite tacks: port-tack vessel gives way to starboard-tack vessel. Same tack: vessel on windward side gives way to leeward vessel.
Rule 19 — Restricted Visibility in Detail
Rule 19 is the most misunderstood rule on the exam. Students confuse fog signals with right-of-way. There IS no right-of-way in restricted visibility. Every vessel is responsible for avoiding close-quarters situations.
What Rule 19 REQUIRES
- ✓ Safe speed adapted to conditions
- ✓ Engines ready for immediate maneuver
- ✓ Use all available means including radar
- ✓ Sound fog signals at correct intervals
- ✓ Avoid close-quarters situations proactively
Fog Signal Forward of the Beam
If you hear a fog signal apparently forward of your beam, you MUST reduce speed to bare steerageway or stop engines and navigate with extreme caution until danger of collision is over.
Frequently Asked Questions
What is the Rule 18 hierarchy in COLREGS?
Rule 18 establishes the responsibility hierarchy between vessels. From highest privilege to most give-way duty: (1) Not Under Command (NUC), (2) Restricted in Ability to Maneuver (RAM), (3) Constrained by Draft (CBD — international only), (4) engaged in fishing or trawling, (5) sailing vessels, (6) power-driven vessels, (7) seaplanes. Every vessel must keep clear of those above it in the hierarchy. A key exam point: the Inland Rules do not recognize CBD as a privileged class.
What is the difference between a give-way vessel and a stand-on vessel?
The give-way vessel (formerly called burdened vessel) must take early and substantial action to keep well clear of the stand-on vessel. The stand-on vessel (formerly called privileged vessel) must maintain its course and speed so the give-way vessel can predict its position. The stand-on vessel may take action only if it becomes apparent that the give-way vessel is not taking appropriate action, and must take action when collision is imminent. Rule 16 governs give-way actions; Rule 17 governs stand-on duties.
What are the three encounter situations under COLREGS and how are they resolved?
The three meeting situations are: (1) Head-on (Rule 14) — both vessels must alter course to starboard so each passes on the port side of the other; applies when vessels meet approximately bow-to-bow. (2) Crossing (Rule 15) — the vessel with the other on its starboard side is the give-way vessel; it must take action to avoid crossing ahead of the stand-on vessel. (3) Overtaking (Rule 13) — the overtaking vessel must keep clear regardless of which rules would otherwise apply; overtaking begins when coming from more than 22.5 degrees abaft the beam.
What does Rule 19 say about restricted visibility?
Rule 19 applies when vessels are NOT in sight of each other due to fog, rain, or other reduced visibility. Critically, the crossing, head-on, and overtaking rules (Rules 13-17) do NOT apply. Every vessel must proceed at safe speed adapted to conditions, have engines ready for immediate maneuver, and use radar if available. If a vessel hears a fog signal forward of the beam or cannot avoid a close-quarters situation, it must reduce speed to bare steerageway or stop. There is no give-way or stand-on designation in restricted visibility.
What is the Inland Rule difference for whistle signals in a narrow channel?
Under Inland Rules, when vessels are in sight of each other, a vessel intending to overtake must sound a whistle signal AND receive an agreement signal before proceeding: 1 prolonged plus 1 short blast to overtake on the starboard side, or 1 prolonged plus 2 short blasts to overtake on the port side. The overtaken vessel must sound the same signal back to agree. Under International COLREGS, the overtaking vessel sounds 2 long plus 1 short (starboard) or 2 long plus 2 short (port) but no agreement is required.
What does RAM stand for and what vessels qualify?
RAM stands for Restricted in Ability to Maneuver. Rule 3(g) defines RAM vessels as those restricted by the nature of their work from maneuvering as required by the rules: vessels laying, servicing, or picking up a navigation mark, submarine cable, or pipeline; vessels engaged in dredging, surveying, or underwater operations; vessels engaged in replenishment or transferring persons, provisions, or cargo at sea; vessels launching or recovering aircraft; vessels engaged in mine clearance operations; and vessels engaged in towing operations that severely restrict maneuverability. RAM is second only to NUC in the Rule 18 hierarchy.
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