The Rules of the Road are the most heavily tested topic on every USCG captain's license exam. This guide covers all COLREGS rules from 2 through 37 with emphasis on the specific rules, scenarios, vessel categories, lights, and signals that appear most frequently on the OUPV (six-pack) and Master exams.
Before the steering and sailing rules can be applied, mariners must understand the foundational rules that set the framework for all COLREGS. These rules are frequently tested in scenario form.
Rule 2 is the cornerstone of COLREGS philosophy. It contains two critical provisions:
Exam Key Point
When an exam question asks whether you can violate COLREGS, the answer is yes — Rule 2 permits departures from the rules when necessary to avoid immediate danger. However, Rule 2 is not a license for negligence. Good seamanship is always required in addition to rule compliance.
Every vessel must at all times maintain a proper lookout by sight and hearing as well as by all available means appropriate to prevailing circumstances and conditions.
Required Methods
Common Violations
Every vessel must proceed at a safe speed so that proper and effective action can be taken to avoid collision and be stopped within a distance appropriate to prevailing circumstances. Rule 6 does not set a number — it requires judgment.
Factors in determining safe speed include:
All Vessels
Radar-Equipped Vessels (Additional)
Exam Trap
"Safe speed" does not always mean slow speed. In clear visibility with no traffic, a higher speed may be perfectly safe. The question is always: can proper action be taken and can the vessel be stopped within appropriate distance given all conditions?
Every vessel must use all available means to determine whether risk of collision exists. If there is any doubt, risk of collision is deemed to exist.
The Compass Bearing Rule
The primary tool for determining risk of collision is compass bearing. Take a series of compass bearings on the approaching vessel. If the bearing does not change (steady bearing, decreasing range), collision risk exists. Even a slowly changing bearing may indicate risk with a large vessel at close range.
Rule 7 Requirements
When action to avoid collision is taken, it must meet three criteria:
Positive
Large enough to be readily apparent to the other vessel — no small, tentative changes
Timely
Made in ample time — before the situation becomes critical or the other vessel is forced to act
Safe
Must not create another close-quarters situation or new collision risk with another vessel
Rule 8 also specifies that if sea room permits, action to avoid collision with a vessel forward of the beam should consist of altering course only or reducing speed — slowing or stopping is always a valid Rule 8 action. A 5-degree course alteration does not qualify as "positive" action.
Rule 9 governs navigation in narrow channels or fairways. It is heavily tested because of its specific obligations and the distinctions between vessel types.
Keep to starboard side
A vessel proceeding along a narrow channel must keep as far to the starboard side of the channel as is safe and practicable.
Shall not impede
Vessels under 20m, sailing vessels, and fishing vessels must not impede vessels that can navigate safely only within a narrow channel or fairway. 'Shall not impede' is different from 'give way' — it means do not create a situation requiring the larger vessel to take evasive action.
Crossing vessels
A vessel crossing a narrow channel must not impede a vessel that can navigate safely only within the channel. Rule 9 crossing vessels must give way to vessels confined to the channel.
Overtaking signal (COLREGS)
When overtaking in a narrow channel, the overtaking vessel sounds 1 long + 1 short to pass on the starboard side, or 1 long + 2 short to pass on the port side. The overtaken vessel agrees with the same signal. If unsafe, the overtaken vessel sounds 5 short blasts.
No anchoring in channel
Vessels shall not anchor in a narrow channel except in an emergency.
A Traffic Separation Scheme (TSS) divides opposing traffic into separate lanes using a separation zone or line. Rule 10 governs how all vessels must behave in and near a TSS.
| Vessel/Situation | Rule 10 Obligation |
|---|---|
| Vessel using the lane | Proceed in the general direction of traffic flow for that lane; join/leave at termination points or at as small an angle as practicable from the side |
| Vessel crossing the TSS | Cross at right angles or as nearly right angles as practicable to the general direction of traffic flow |
| Vessels under 20m, sailing vessels, fishing vessels | Must not impede safe passage of power-driven vessels in the traffic lane |
| Vessel engaged in fishing | Must not impede lane traffic; may fish within separation zones (with care) |
| Vessel not using the TSS | Must keep as wide a margin as practicable from the separation zone |
| Emergency/safety anchoring | A vessel may anchor within a TSS in emergency or when safety requires — no other anchoring in TSS |
Rules 13 through 17 define the give-way and stand-on obligations for specific encounter types. These are the highest-frequency rules on the USCG exam. Understanding which rule applies to a given scenario is critical.
A vessel is overtaking when coming up with another vessel from a direction more than 22.5 degrees abaft the beam. The overtaking vessel is always the give-way vessel — regardless of vessel type.
How to Identify Overtaking
Rule 13 Supremacy
Narrow Channel Overtaking Signal (COLREGS)
1 prolonged + 1 short: intend to overtake on your starboard side. 1 prolonged + 2 short: intend to overtake on your port side. Overtaken vessel agrees with same signal or sounds 5 short blasts if unsafe.
A head-on situation exists when two power-driven vessels are meeting on nearly reciprocal courses such that there is risk of collision. Both vessels are equally burdened — both must turn to starboard.
How to Identify a Head-On Situation
Critical Points
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 give way.
Give-Way Vessel
Stand-On Vessel
Every vessel required to keep out of the way of another vessel must take early and substantial action to keep well clear.
Rule 17 has a three-tier structure. Understanding the progression from "must maintain" to "may act" to "must act" is a frequent exam topic.
Tier 1 — Must Maintain (Default)
The stand-on vessel must maintain course and speed. Changing course or speed prematurely can confuse the give-way vessel and create a more dangerous situation.
Tier 2 — May Act (Permissive)
When it becomes apparent the give-way vessel is not taking appropriate action, the stand-on vessel MAY take action to avoid collision by maneuver alone. This is permissive — the stand-on vessel has discretion.
Tier 3 — Must Act (Mandatory)
When collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel MUST take the best action to avoid collision. This obligation is mandatory and overrides the duty to maintain course and speed.
Critical Prohibition
The stand-on vessel must NOT alter course to port for a vessel on her own port side. In a crossing situation, the give-way vessel approaches from starboard. If the stand-on vessel turns to port, the vessels may converge. The stand-on vessel should turn to starboard or slow if action is necessary.
Rule 18 establishes the priority order for all vessels when the encounter type rules (13–17) do not specifically assign give-way status. Memorize this hierarchy — it appears on nearly every USCG exam.
Lights
2 all-round red lights (vertical); sidelights only when making way
Day Shape
2 balls (vertical)
Notes
Highest right-of-way; vessel unable to maneuver due to exceptional circumstance
Lights
Red-white-red all-round lights (vertical); sidelights and stern light when making way
Day Shape
Ball-diamond-ball (vertical)
Notes
Dredging, mine clearing, cable laying, replenishment at sea, launching/recovering aircraft
Lights
3 all-round red lights (vertical) + normal underway lights
Day Shape
Cylinder
Notes
COLREGS only — not a category under Inland Rules
Lights
Green over white (trawling); red over white (other fishing) + sidelights if making way
Day Shape
2 cones apex together (vertical)
Notes
Trolling lines only = NOT engaged in fishing under COLREGS
Lights
Sidelights + sternlight; optional bicolor/tricolor (under 20m)
Day Shape
No specific day shape
Notes
Engine engaged = power-driven vessel even if sails are set
Lights
Masthead(s) + sidelights + sternlight
Day Shape
No shape; cone apex down if proceeding under sail and engine
Notes
Lowest in hierarchy — must give way to all five categories above
A NUC is a vessel unable to maneuver as required by the Rules due to some exceptional circumstance. Examples: engine failure, steering gear failure, loss of propulsion.
NUC Displays:
Rule 19 is the most misunderstood rule on the exam. It governs conduct when vessels are not in sight of one another due to fog, rain, haze, or other conditions. Rules 12-18 do not apply in restricted visibility — Rule 19 governs exclusively.
Safe Speed
Every vessel must proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. Engines must be ready for immediate maneuver.
Radar Target Forward of Beam
If a vessel detects by radar alone another vessel forward of the beam, do NOT alter course to port (unless overtaking). Consider reducing speed substantially or stopping.
Fog Signal Forward of Beam
If you hear a fog signal forward of the beam (other than from a vessel being overtaken), reduce to bare steerageway or stop and navigate with great caution until the danger of collision is past.
No Stand-On in Fog
Rules 12-18 do NOT apply. There is no stand-on vessel and no give-way vessel in restricted visibility. Both vessels bear equal obligation to avoid collision.
Radar is Not Optional
If radar is available, it must be used. Radar information must be actively monitored and plotted. A clean radar screen does not mean the area is clear.
| Issue | Clear Weather (Rules 12-18) | Restricted Visibility (Rule 19) |
|---|---|---|
| Give-way/stand-on | Applies — one vessel gives way | Does NOT apply — equal obligation |
| Vessels in sight | Yes — visual contact established | No — not in sight of each other |
| Action trigger | Crossing, head-on, or overtaking | Radar detection or fog signal |
| Port alteration prohibition | Stand-on must not turn to port (Rule 17) | No vessel should alter to port for a radar target forward of beam |
| Speed requirement | Safe speed (Rule 6) | Safe speed adapted to restricted visibility specifically |
| Fog signal ahead | N/A (vessels in sight) | Reduce to bare steerageway or stop |
Rules 20-31 define the lighting and day-shape requirements for every vessel type. Lights questions constitute a large portion of the USCG exam. Learn the pattern: what type of vessel, how many lights, what color, what arc, and what visibility range.
| Light | Color | Arc | Description |
|---|---|---|---|
| Masthead light | White | 225° | From right ahead to 22.5° abaft the beam on each side |
| Sidelight (port) | Red | 112.5° | From right ahead to 22.5° abaft the port beam |
| Sidelight (starboard) | Green | 112.5° | From right ahead to 22.5° abaft the starboard beam |
| Sternlight | White | 135° | From 67.5° on each side of dead astern |
| Towing light | Yellow | 135° | Same arc as sternlight; replaces or supplements sternlight on towing vessel |
| All-round light | Any | 360° | Visible on the horizon from any direction; used for anchor, NUC, RAM, CBD, fishing lights |
| Flashing light | Yellow | 360° | Hovercraft in non-displacement mode; also used for some WIG craft |
The most commonly tested vessel lighting configurations
| Vessel Type | Forward | Sides | Stern/Other | Special |
|---|---|---|---|---|
| Power-driven vessel underway (under 50m) | 1 masthead light (forward) | Sidelights | Sternlight | — |
| Power-driven vessel underway (50m or more) | 1 masthead light (forward) | Sidelights | Sternlight | — |
| Sailing vessel underway (under 20m) | — | Sidelights (or bicolor) | Sternlight (or combined tricolor at masthead) | Optional: red over green all-round at masthead |
| Vessel at anchor (under 50m) | — | — | — | 1 all-round white light (forward part of vessel) |
| Vessel at anchor (50m or more) | — | — | — | All-round white forward + all-round white aft (lower) |
| Vessel Not Under Command | — | Sidelights if making way | Sternlight if making way | 2 all-round red lights (vertical) |
| Vessel Constrained by Draft | Masthead | Sidelights | Sternlight | 3 all-round red lights (vertical) |
| Vessel engaged in fishing (trawling) | — | Sidelights if making way | Sternlight if making way | Green over white all-round lights |
| Vessel engaged in fishing (not trawling) | — | Sidelights if making way over 2 knots | Sternlight if making way over 2 knots | Red over white all-round lights |
| Vessel towing (tow under 200m, pushing ahead) | 2 masthead lights (vertical) | Sidelights | Sternlight + towing light (yellow) | — |
| Vessel towing (tow over 200m) | 3 masthead lights (vertical) | Sidelights | Sternlight + towing light (yellow) | Diamond shape by day |
A vessel restricted in ability to maneuver displays:
Rules 32-37 cover whistle signals, distress signals, and fog signals. The distinction between COLREGS and Inland whistle signal usage is the most frequently tested concept in this section.
COLREGS (International)
Whistle signals are maneuver signals — sounded as you execute the maneuver to inform the other vessel of what you are doing.
Inland Rules
Whistle signals are intent and agreement signals — proposed before maneuver; the other vessel must agree before you proceed.
| Signal | Meaning | When Sounded | Rule |
|---|---|---|---|
| 1 short blast | I am altering my course to starboard | Inland: Intent signal before maneuver. COLREGS: Maneuver signal during maneuver. | Steering/sailing rules |
| 2 short blasts | I am altering my course to port | Inland: Intent signal before maneuver. COLREGS: Maneuver signal during maneuver. | Steering/sailing rules |
| 3 short blasts | I am operating astern propulsion | Both Inland and COLREGS — signals use of reverse thrust, not necessarily moving backward | Steering/sailing rules |
| 5 or more short blasts | Danger / doubt signal | Any time doubt exists about another vessel's intention — mandatory to sound | Rule 34 |
| 1 prolonged blast | Warning when approaching a bend or area where other vessels may be obscured | Rule 34(e) — sounded on approaching a blind bend | Rule 34 |
| 1 prolonged + 2 short | Restricted in ability to maneuver, vessel not under command, sailing, fishing, towing/pushing | Fog signal every 2 minutes | Rule 35 |
| 1 prolonged + 3 short | Vessel being towed (last vessel in tow) | Fog signal every 2 minutes if manned | Rule 35 |
| 2 prolonged blasts | Power-driven vessel stopped, making no way | Fog signal every 2 minutes | Rule 35 |
| Bell (rapid 5 sec) + optional gong aft | Vessel at anchor | Bell every 1 minute; vessels over 100m also ring gong aft | Rule 35 |
| 3 bell strokes + rapid ring + 3 bell strokes | Vessel aground | In addition to anchor bell signal | Rule 35 |
— — — — —
5 or more short blasts
Must be sounded whenever doubt exists about another vessel's intentions. This signal is mandatory when danger exists — it is not optional. Either vessel may sound it. May be supplemented by at least 5 short and rapid flashes.
Annex IV lists the authorized distress signals. Key signals to know:
These are the concepts where candidates most frequently lose points. Each trap represents a distinction that is counterintuitive or easily confused with a related rule.
Rule 25
The moment the engine is engaged, the vessel is legally a power-driven vessel — even if sails are still set. She must display a cone shape (apex downward) by day. She loses all privileges of a sailing vessel under Rule 18.
Rule 3(d)
No. Trolling lines, hook and line, or rod-and-reel fishing does NOT constitute 'engaged in fishing' under COLREGS. Only vessels with nets, lines, or trawls that restrict maneuverability qualify. A sport fisherman trolling is a power-driven vessel.
Rule 18 / Inland Rules
Constrained by Draft (CBD) is a COLREGS category only. The Inland Rules do not recognize CBD status. A deep-draft vessel in inland U.S. waters has no special right-of-way based on draft alone.
Rule 17
Prohibited. The stand-on vessel in a crossing situation must not alter course to port if the give-way vessel is on its port side. Turning to port could bring the vessels into a head-on situation or make matters worse. Rule 17 explicitly prohibits this action.
Rule 19
False. In restricted visibility, Rules 12-18 do not apply at all. Rule 19 governs exclusively. There is no stand-on or give-way vessel in fog — both vessels have equal obligation to navigate safely. This is one of the most commonly missed exam points.
Rule 13 / 18
Not when overtaking. If a sailing vessel is overtaking a power-driven vessel, the sailing vessel is the give-way vessel under Rule 13 — period. Rule 13 supersedes Rule 18. Also, sailing vessels have equal standing with fishing vessels and must give way to RAM and NUC vessels.
Rules 34 / 88
Different systems. Under COLREGS, whistle signals are maneuver signals (sounded as you execute). Under Inland Rules, they are intent and agreement signals (proposed before maneuver, requires the other vessel to agree with the same signal before proceeding). On the exam, context matters — international waters vs. inland waters changes the protocol entirely.
Rule 9
Rule 9 applies specifically to 'narrow channels or fairways' — it is not triggered by any constricted water. The channel must be one where vessels must navigate near the center to stay in safe water. The 'shall not impede' obligation applies to vessels under 20m, sailing vessels, and fishing vessels relative to vessels that can only safely navigate within the channel.
Rule 7
False. Even a slowly changing bearing may still involve collision risk, especially with a large vessel or at close range. Rule 7 says that if bearing is appreciably changing, risk of collision may not exist — but there is no bright line. When in doubt, assume risk exists.
Rule 23
Only required for vessels 50 meters or more in length. Vessels under 50m may carry a second masthead light, but it is not required. The second masthead light, when carried, must be higher than and abaft the forward masthead light.
These questions appear regularly on USCG OUPV and Master exams and in student study sessions.
Rule 2 is the Responsibility rule. It states that nothing in the rules exonerates any vessel, owner, master, or crew from the consequences of neglect to comply with the rules, or from neglect of any precaution required by the ordinary practice of seamen. It also gives mariners the right — and duty — to depart from the rules when necessary to avoid immediate danger. On the exam, Rule 2 appears in questions asking whether you can ever violate COLREGS (answer: yes, when necessary to avoid collision), and in seamanship judgment questions. Rule 2 is sometimes called the 'good seamanship' escape clause.
Rule 5 requires every vessel to maintain a proper lookout at all times by sight, hearing, and all available means appropriate to the prevailing circumstances. 'All available means' includes radar, AIS, VHF radio, and any other technology on board. A proper lookout is not just visual — it includes sound. On exam questions, Rule 5 is violated when a vessel relies solely on radar without a visual watch, when a single person attempts to both steer and keep watch on a vessel that requires separation of those duties, or when hearing protection prevents detection of sound signals.
Rule 8 requires any action taken to avoid collision to be positive, made in ample time, and in keeping with good seamanship. Course or speed changes must be large enough to be readily apparent to the other vessel — a 5-degree course alteration does not qualify. Action must be taken in ample time, meaning before the situation becomes critical. Rule 8 also requires that when altering course, you must not create another collision risk. If sea room permits, slowing or stopping is always a valid action under Rule 8. This rule governs the 'how' of avoidance; other rules determine the 'who must give way.'
Rule 18 establishes which vessel has priority when two vessels meet. From highest right-of-way to lowest: (1) Vessel Not Under Command (NUC); (2) Vessel Restricted in Ability to Maneuver (RAM); (3) Vessel Constrained by Draft (CBD — COLREGS only, not Inland); (4) Vessel Engaged in Fishing with gear deployed; (5) Sailing vessel under sail alone; (6) Power-driven vessel underway. A power-driven vessel must give way to all five categories above it. Critical exception: Rule 13 (overtaking) always supersedes Rule 18 — an overtaking vessel is the give-way vessel regardless of its type. CBD vessels have no special status under Inland Rules.
Under Rule 23, a power-driven vessel underway must display: (1) a masthead light forward (white, 225 degrees, visible 5 miles for vessels 50m or more); (2) a second masthead light aft and higher than the forward masthead light (vessels 50m or more must carry this; vessels under 50m may carry it); (3) sidelights — red on the port side, green on the starboard side (each 112.5 degrees, visible 2 miles for vessels under 50m, 3 miles for 50m or more); (4) a sternlight — white, 135 degrees, visible 2 miles. Vessels under 7 meters that cannot comply may use a white all-around light. Vessels under 12 meters may combine the sidelights into a single bicolor lantern.
Rule 35 requires: (1) Power-driven vessel making way through the water — one prolonged blast at intervals of not more than 2 minutes; (2) Power-driven vessel underway but stopped and making no way — two prolonged blasts in succession with an interval of about 2 seconds, at intervals of not more than 2 minutes; (3) Sailing vessel, vessel not under command, RAM, CBD, fishing vessel, or towing/pushing vessel — three blasts (one prolonged + two short) at intervals of not more than 2 minutes; (4) A vessel being towed — four blasts (one prolonged + three short) as the last signal in the sequence. Vessels at anchor ring the bell rapidly for about 5 seconds at intervals of not more than one minute.
The most common Rule 9 trap is the 'shall not impede' duty. Rule 9 states that a vessel less than 20 meters in length, a sailing vessel, or a vessel engaged in fishing shall not impede a power-driven vessel that can navigate safely only within the narrow channel. Many candidates confuse 'shall not impede' with 'give way' — these are different duties. The smaller vessel must not create a situation where the larger vessel must take evasive action, but the larger vessel still has Rule 2 responsibilities. A second trap: fishing vessels may NOT anchor in a narrow channel except in emergencies, and crossing vessels must not impede vessels confined to the channel. The signal for overtaking in a narrow channel (international) is one prolonged plus one short blast for starboard-side passing.
A vessel Constrained by Draft (CBD) is a power-driven vessel that, 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. CBD is a COLREGS category only — the Inland Rules do not recognize CBD status. CBD vessels display three all-around red lights in a vertical line, or a cylinder shape by day. CBD vessels must still navigate with great care and have full regard for their special condition. They are not exonerated from collisions — Rule 2 still applies. On the exam, CBD questions often test whether the category applies in U.S. inland waters (it does not).
Reading about Rules of the Road is just the first step. NailTheTest delivers scenario-based COLREGS questions matched to the actual USCG exam format — with immediate feedback and detailed explanations for every answer.
No signup required to start. OUPV and Master license prep.