Crossing, head-on, and overtaking situations — plus stand-on vs. give-way duties, privilege hierarchy, narrow channels, and restricted visibility. Everything you need to nail the exam.
Rules 13–19
Core right-of-way rules tested on every USCG exam
90%
Passing threshold — Rules of the Road section
7
Vessel types in the privilege hierarchy
Every vessel must give way to all vessels ranked above it. The higher the rank, the greater the right of way. Memorize this top-to-bottom: NUC → RAM → CBD → Fishing → Sailing → Power.
Not Under Command (NUC)
Highest PriorityRule 3(f) / Rule 27
Unable to maneuver due to exceptional circumstance (steering failure, engine loss). Cannot comply with rules.
Restricted in Ability to Maneuver (RAM)
Rule 3(g) / Rule 27
Working limitations prevent compliance — dredging, diving ops, mine clearing, cable laying, underway replenishment.
Constrained by Draft (CBD)
International OnlyRule 3(h) / Rule 28 — International only
Deep draft vessel unable to deviate from its course due to available depth. NOT recognized under U.S. Inland Rules.
Engaged in Fishing
Rule 3(d) / Rule 26
Fishing with nets, lines, or trawls that restrict maneuverability. NOT vessels with trolling lines only.
Under Sail
Rule 12 / Rule 25
Vessel proceeding under sail alone. A vessel using engine + sail displays a cone forward and is treated as power.
Power-Driven Vessel Underway
Rule 18
Any vessel propelled by machinery. Highest give-way duties against all other vessel types above.
Seaplane
Lowest PriorityRule 18(e)
Must keep clear of all vessels and avoid impeding their navigation.
Critical Override: Rule 13 (Overtaking)
The overtaking rule overrides the entire hierarchy. Any vessel overtaking another must keep clear — regardless of type. A sailboat overtaking a powerboat must give way to that powerboat until completely past and clear. When in doubt whether you are overtaking, assume you are.
A crossing situation exists when two power-driven vessels are meeting on intersecting courses such that risk of collision exists and neither is overtaking. The rule: the vessel that has the other on its starboard side is the give-way vessel.
// Diagram: Two vessels on crossing courses
[Vessel A] ──────────→ (heading East)
╲
╲ [Vessel B] (heading North)
Vessel B has Vessel A on its starboard side → Vessel B is GIVE-WAY
Vessel A has Vessel B on its port side → Vessel A is STAND-ON
STAND-ON VESSEL (Rule 17)
Maintain course and speed. You see the other vessel's RED (port) sidelight — you have right of way.
GIVE-WAY VESSEL (Rule 16)
Take early, substantial action. Avoid crossing ahead of the stand-on vessel. You see their GREEN (starboard) light.
THE RED LIGHT RULE (Exam Shortcut)
Red light = you are looking at their port side = they are on your starboard = you are STAND-ON. Green light = you are looking at their starboard = they are on your port = you must GIVE WAY.
A head-on situation exists when two power-driven vessels are meeting on reciprocal or nearly reciprocal courses and risk of collision exists. You can see both sidelights of the other vessel (both red and green). The rule: both vessels alter course to starboard and pass port-to-port.
// Diagram: Two vessels head-on
[Vessel A] ──────────→ (heading East)
←──────── [Vessel B] (heading West)
Both alter course to starboard → pass each other port-to-port
Neither vessel has "right of way" — both must act
INLAND RULES (whistle agreement)
Both vessels sound one short blast to signal starboard alteration. The other vessel replies with one short blast (agreement). If no agreement: five short blasts (danger signal).
INTERNATIONAL COLREGS (no mandatory exchange)
Both vessels alter to starboard. No mandatory signal exchange required before altering. One short blast signals the alteration being made.
WHEN IN DOUBT
Rule 14(c): When a vessel is in doubt whether a head-on situation exists, it shall assume it does and act accordingly — alter to starboard.
A vessel is overtaking when it is coming up on another vessel from a direction more than 22.5° abaft the beam of the vessel ahead — i.e., from the sternlight arc. The rule: the overtaking vessel must keep clear until completely past and clear. No exceptions.
// Diagram: Overtaking — coming from the sternlight arc
[Vessel A] ──→ (slower, being overtaken)
[Vessel B] ─────────────────→ (faster, overtaking)
Vessel B comes from >22.5° abaft Vessel A's beam → can only see A's sternlight (white)
Vessel B is GIVE-WAY regardless of type — even if it's a sailboat overtaking a powerboat
RULE 13 OVERRIDES RULE 18 HIERARCHY
A sailing vessel overtaking a power vessel must give way to the power vessel. A RAM vessel overtaking a NUC vessel must give way. The overtaking rule is absolute and permanent until the vessel is completely past and clear.
DOUBT = OVERTAKING
Rule 13(d): If a vessel is in any doubt whether it is overtaking, it must assume it is and keep clear accordingly.
| Aspect | Stand-On Vessel (Rule 17) | Give-Way Vessel (Rule 16) |
|---|---|---|
| Initial obligation | Maintain course and speed | Take early and substantial action to keep well clear |
| When give-way vessel is not acting | May take action as soon as it becomes apparent (Rule 17(a)(ii)) | Must act — failure to give way is a rules violation |
| When collision is imminent | Must take action — cannot avoid collision by stand-on alone (Rule 17(b)) | Must continue to give way; take all possible action |
| Preferred maneuver | If action needed, avoid turning to port when the other vessel is to port | Avoid crossing ahead of the stand-on vessel |
| Sound signal when taking action | 5 short blasts (doubt/danger) or 1/2 short blasts (action) | 5 short blasts if disagreeing with the stand-on vessel's signal |
| Limits of right of way | Right of way does NOT permit reckless navigation — Rule 2 (seamanship) always applies | Must maneuver broadly and early — a last-minute small alteration does not comply |
Every vessel shall keep to the starboard side of the channel as far as is safe and practicable — the maritime equivalent of driving on the right side of the road.
A vessel under 20 meters in length or a sailing vessel shall not impede the passage of a vessel that can only safely navigate within the channel.
A vessel crossing a narrow channel shall not impede vessels using the channel. If doubt exists, sound five short blasts.
Under Inland Rules, an overtaking vessel signals intent (1 prolonged + 1 short for starboard pass; 1 prolonged + 2 short for port pass) and must wait for the ahead vessel's agreement before passing.
A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway.
No vessel shall anchor in a narrow channel if it can be avoided. If anchoring is unavoidable, the vessel must take all necessary precautions.
Rule 9 vs. Rule 18: The Impeding Distinction
Rule 9 says certain vessels "shall not impede" — this is different from "give way." A small vessel must not put itself in a position where the larger vessel must take emergency action. But once a close-quarters situation develops, the normal give-way/stand-on rules of Rules 13–17 apply.
Traffic Separation Schemes (TSS) are designated shipping lanes in congested waters — similar to a highway with divided lanes. Rule 10 governs how vessels must behave within them.
Vessels using a TSS shall proceed in the appropriate traffic lane in the general direction of traffic flow.
A vessel shall join or leave a traffic lane at the termination points. If joining or leaving from the side, do so at as small an angle as practicable.
A vessel crossing a TSS shall do so on a heading as nearly as practicable at right angles to the general direction of traffic flow. This minimizes time in the lane.
A vessel shall not enter a separation zone or cross a separation line except: in an emergency, to avoid immediate danger, or to engage in fishing within the zone.
A vessel not using the TSS shall avoid it by as wide a margin as practicable.
Vessels under 20m, sailing vessels, and fishing vessels shall not impede power vessels following traffic lanes. The big ships cannot deviate easily.
Rule 19 applies when vessels are not in sight of one another due to fog, rain, haze, snow, or similar conditions. When you cannot see the other vessel (only detect it on radar), the normal right-of-way rules are suspended. All vessels have equal duty to avoid collision.
All vessels must proceed at a safe speed adapted to the prevailing conditions. Factors: state of visibility, traffic density, maneuverability, background lights, wind and sea state.
Power-driven underway: 1 prolonged blast every 2 minutes. Sailing vessel, fishing, towing: 1 prolonged + 2 short every 2 minutes. Vessel at anchor: rapid bell (5 sec) every minute.
If you detect a vessel forward of your beam on radar, you must not alter course to port (toward the contact). Alter to starboard instead, or reduce speed.
For a vessel detected abeam or abaft the beam, avoid any action that would result in passing close ahead of that vessel.
Inland Difference: Passing Agreements
Inland Rules whistle-to-whistle passing agreements (one short blast / two short blasts exchanges) only apply when vessels are in sight of one another. In restricted visibility, you cannot signal intentions this way — fog signals under Rule 35 are the only required sound signals. No crossing/overtaking agreements apply.
The #1 most-tested trap: an overtaking sailboat vs. a power vessel. Answer: the sailboat must give way (Rule 13 beats Rule 18). Always check for overtaking before applying the hierarchy.
Crossing questions always hinge on which sidelight you see. Red light = you have ROW. Green light = you give way. Practice this until it's automatic.
NUC has the highest privilege in the hierarchy — but an overtaking NUC vessel still must give way to the vessel it's overtaking. Rule 13 is universal.
If the question says 'inland waters,' CBD does not exist. Only pick CBD as an answer for international waters / high seas questions.
Any question mentioning fog, reduced visibility, or radar-only detection: Rules 13–15 are off. Apply Rule 19 — safe speed, no port alteration for forward contacts, fog signals.
Rule 17 questions often test: must the stand-on vessel always maintain course? No — once collision is imminent, the stand-on vessel MUST act. Being stand-on does not mean passive.
'Shall not impede' (small vessels/sailing in channels) is a different obligation than the give-way duty. The exam distinguishes these. Impede = don't create a situation requiring emergency action.
A vessel is 'engaged in fishing' only if it uses gear that restricts maneuverability (trawls, nets, lines with floats). Trolling lines do not qualify — a trolling boat is treated as a power vessel.
Under Rule 15, the vessel that has the other on its starboard side is the give-way vessel. The vessel on the left (with the other vessel to its right/starboard) must give way. A helpful memory aid: if you see the other vessel's red (port) light, you are the stand-on vessel. If you see their green (starboard) light, you are the give-way vessel — the 'green means go, red means stop' rule.
A stand-on vessel must initially maintain its course and speed so the give-way vessel can predict its position and maneuver safely. However, Rule 17(b) permits the stand-on vessel to take action once it becomes apparent the give-way vessel is not acting appropriately. Rule 17(c) requires the stand-on vessel to take action if collision is imminent — at that point it must maneuver to avoid. Being 'stand-on' does not mean passive — the duty to avoid collision overrides everything.
Yes. Rule 13 (Overtaking) overrides the privilege hierarchy of Rule 18. Any vessel overtaking another must keep clear, regardless of vessel type. A sailboat overtaking a powerboat must give way to that powerboat until it is completely past and clear. The overtaking rule is absolute — it applies even if the overtaking vessel would normally have higher priority under the hierarchy.
Under Rule 19, when vessels are not in sight of one another due to fog, rain, or other conditions, the crossing, head-on, and overtaking rules (Rules 13–15) do NOT apply. All vessels must proceed at a safe speed for the conditions, maintain a proper radar watch, sound fog signals, and be ready to stop. If you detect another vessel forward of your beam on radar, you must avoid altering course to port. Avoid any action that would take you alongside another vessel.
Rule 9 requires vessels in narrow channels to keep as far to the starboard side of the channel as is safe and practicable — analogous to driving on the right side of the road. A vessel less than 20 meters in length or a sailing vessel shall not impede vessels that can only navigate safely within the channel. Crossing vessels must not impede vessels using the channel. Overtaking in a narrow channel requires prior agreement by the vessel being overtaken via sound signals.
A vessel Not Under Command (NUC) is one that through some exceptional circumstance is unable to maneuver as required by the rules — for example, a steering failure, disabled engine, or a vessel aground. Because it physically cannot maneuver to give way, every other vessel must give way to it. NUC is indicated by two all-around red lights vertically displayed at night, and two balls vertically by day. The NUC vessel sounds the same fog signals as a power-driven vessel underway.
No. Constrained by Draft (CBD) under Rule 28 is an International COLREGS designation only. It is not recognized under U.S. Inland Rules. On the exam, when a question specifies 'inland waters,' do not apply CBD privilege. A CBD vessel displays three all-around red lights vertically, or a blue cylinder by day, under international rules only.
The 'red light rule' is a memory aid for COLREGS crossing situations: if you see the other vessel's red (port) sidelight, you are on that vessel's starboard side — meaning YOU have the right of way (stand-on). If you see the other vessel's green (starboard) sidelight, the other vessel is on your starboard side — you are the give-way vessel. Red = you have right of way. Green = you must give way.
Full Part B overview: hierarchy, lights, signals, exam strategy
Complete ColRegs structure, rule numbers, and sound signals
Every fog signal, maneuvering blast, and danger signal explained
Light configurations by vessel type, arc requirements
Where Inland Rules differ from International COLREGS
Section-by-section strategy and scoring breakdown
1,628+ USCG exam questions with detailed explanations — including hundreds of crossing, overtaking, and head-on scenario questions. Spaced repetition so you actually retain it.
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