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Navigation Rules Flash Cards
95 cards covering the International Rules (72 COLREGS) and the U.S. Inland Rules, including the places the two disagree. Tap a card to flip it. Mark what you know and the deck narrows to what you don't. Nothing is sent anywhere — your progress stays in this browser.
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The complete deck, grouped by part. Click any question to see the answer — useful for browsing, searching the page, or printing.
General & Definitions
Rules 1–3 · 10 cards
Where do the International Rules (COLREGS) apply?
On the high seas and in all waters connected to them that are navigable by seagoing vessels. Inside the COLREGS Demarcation Lines set by the Coast Guard, the U.S. Inland Rules (33 CFR Part 83) apply instead.
Rule 1
What does Rule 2 (Responsibility) require beyond the letter of the Rules?
Nothing in the Rules excuses any vessel, owner, master, or crew from the consequences of neglecting them — or of neglecting any precaution required by the ordinary practice of seamen or by the special circumstances of the case.
Rule 2
Define "underway."
Not at anchor, not made fast to the shore, and not aground. A vessel drifting with the engine off is still underway — it just is not making way (moving through the water).
Rule 3
What is a "vessel not under command" (NUC)?
A vessel that, through some exceptional circumstance, is unable to maneuver as the Rules require and therefore cannot keep out of the way of another vessel.
Rule 3
What is a "vessel restricted in her ability to maneuver" (RAM)?
A vessel whose work restricts her ability to keep out of the way: dredging, surveying, underwater operations, replenishment at sea, launching or recovering aircraft, minesweeping, or towing.
Rule 3
Is a boat trolling lines a "vessel engaged in fishing"?
No. Fishing means nets, lines, or trawls that restrict maneuverability. Trolling lines do not, so a trolling boat is treated as an ordinary power-driven vessel.
Rule 3
When is a sailboat a "sailing vessel" under the Rules?
Only when under sail and her propelling machinery is not being used. Sails up with the engine running makes her a power-driven vessel.
Rule 3
What counts as "restricted visibility"?
Any condition limiting sight: fog, mist, falling snow, heavy rainstorms, sandstorms, or similar causes.
Rule 3
What is a "vessel constrained by her draft"?
A power-driven vessel that, because of her draft relative to the available depth and width of water, is severely restricted in her ability to deviate from her course.
Rule 3
Memory aid: which sidelight is which?
Port wine is red — port takes the red light, and port is left. Starboard takes green. Two more: "there is no red port left in the bottle," and port/left are both four letters.
Rule 21
Steering & Sailing
Rules 4–19 · 23 cards
What does Rule 5 require of every vessel, at all times?
A proper look-out by sight and hearing, and by all other available means appropriate to the circumstances, so as to make a full appraisal of the situation and of the risk of collision.
Rule 5
What is "safe speed"?
A speed at which the vessel can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. It is not a fixed number.
Rule 6
Name the factors in determining safe speed.
Visibility; traffic density; the vessel's maneuverability (stopping distance and turning ability); background light at night; proximity of navigational hazards; draft against available depth. With radar: its range and resolution, sea state and weather effects, and the number, location, and movement of vessels detected.
Rule 6
When must risk of collision be assumed to exist?
Whenever there is any doubt. Risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change — and may exist even with an appreciable bearing change when approaching a very large vessel or a tow at close range.
Rule 7
What are the four qualities of a proper collision-avoidance action?
It must be positive, made in ample time, and with due regard to good seamanship; large enough to be readily apparent to another vessel watching visually or by radar; result in passing at a safe distance; and not create a new close-quarters situation.
Rule 8
What may a vessel do if more time is needed to assess a situation?
Slacken speed, or take all way off by stopping or reversing her means of propulsion.
Rule 8
Which side of a narrow channel do you keep to?
As near to the outer limit of the channel on your starboard side as is safe and practicable.
Rule 9
Who must not impede a vessel that can navigate only within a narrow channel?
A vessel under 20 m, a sailing vessel, and a vessel engaged in fishing. No vessel may cross a narrow channel if doing so impedes a vessel that can safely navigate only inside it.
Rule 9
How do you join or leave a traffic lane?
At the termination point of the lane where possible; otherwise at as small an angle as practicable — crossing a lane is done at a right angle to the general direction of traffic flow.
Rule 10
Two sailing vessels with the wind on different sides — who gives way?
The vessel with the wind on her port side keeps out of the way.
Rule 12
Two sailing vessels with the wind on the same side — who gives way?
The windward vessel keeps out of the way of the leeward vessel. The windward side is the side opposite to the side on which the mainsail is carried.
Rule 12
When is a vessel "overtaking"?
When coming up with another vessel from a direction more than 22.5° abaft her beam — i.e. at night you would see only her stern light, neither sidelight. If in doubt, assume you are overtaking.
Rule 13
Does an overtaking vessel ever become a crossing vessel?
No. No later change in bearing between the two vessels makes the overtaking vessel a crossing vessel or relieves her of the duty to keep clear until finally past and clear.
Rule 13
Two power-driven vessels meeting head-on — what does each do?
Each alters course to starboard, so that each passes on the port side of the other. If in doubt whether the situation is head-on, assume it is.
Rule 14
Two power-driven vessels crossing — who gives way?
The vessel that has the other on her own starboard side gives way, and shall avoid crossing ahead of the other if circumstances permit. "If to starboard red appear, 'tis your duty to keep clear."
Rule 15
What is required of the give-way vessel?
Early and substantial action to keep well clear.
Rule 16
What does the stand-on vessel do?
Keep her course and speed. She may maneuver on her own once it becomes apparent the give-way vessel is not taking appropriate action, and she must act when collision cannot be avoided by the give-way vessel alone.
Rule 17
What one maneuver is the stand-on vessel forbidden?
In a crossing situation she shall not alter course to port for a vessel on her own port side.
Rule 17
Recite the Rule 18 pecking order.
Not under command → Restricted in ability to maneuver → Constrained by draft → Fishing → Sailing → Power-driven. Each gives way to those above it — except where Rules 9, 10, and 13 (narrow channels, traffic schemes, overtaking) say otherwise.
Rule 18
A powerboat and a sailboat in a narrow channel — does power always give way?
No. Rule 18 yields to Rules 9, 10, and 13. A sailing vessel must not impede a vessel that can navigate only within a narrow channel, and an overtaking sailboat still keeps clear of the powerboat it is passing.
Rule 18
You hear a fog signal apparently forward of your beam. What must you do?
Reduce to the minimum speed at which you can be kept on course, take all way off if necessary, and in any event navigate with extreme caution until the danger of collision is over.
Rule 19
What course alteration does Rule 19 tell you to avoid in restricted visibility?
So far as possible, avoid altering course to port for a vessel forward of the beam (other than one being overtaken), and avoid altering toward a vessel abeam or abaft the beam.
Rule 19
Memory aid for the crossing rule.
"If to starboard red appear, 'tis your duty to keep clear." Seeing a red sidelight off your starboard bow means the other vessel is crossing right-to-left and you give way.
Rule 15
Lights & Shapes
Rules 20–31 · 23 cards
When must lights be shown? When are shapes shown?
Lights from sunset to sunrise, and also in restricted visibility during the day. Shapes are shown between sunrise and sunset. The lights rules apply in all weathers.
Rule 20
Arc and color: masthead light.
White, 225° — dead ahead to 22.5° abaft the beam on each side — placed over the fore-and-aft centerline.
Rule 21
Arc and color: sidelights.
Green to starboard, red to port, each showing over 112.5° from dead ahead to 22.5° abaft the beam on its own side.
Rule 21
Arc and color: stern light and towing light.
Stern light: white, 135°, shown as nearly as practicable at the stern. Towing light: the same 135° arc but yellow.
Rule 21
What is a "flashing light" under the Rules?
A light flashing at regular intervals at a rate of 120 or more flashes per minute.
Rule 21
Light ranges for a vessel 50 m or more in length.
Masthead 6 nm; sidelights 3 nm; stern, towing, and all-round lights 3 nm.
Rule 22
Light ranges for a vessel under 12 m.
Masthead 2 nm; sidelights 1 nm; stern, towing, and all-round lights 2 nm.
Rule 22
What lights does a power-driven vessel underway show?
A forward masthead light; a second masthead light abaft of and higher than the first (required at 50 m or more, optional below); sidelights; and a stern light.
Rule 23
What may a power-driven vessel under 7 m and under 7 knots show instead?
A single all-round white light and, if practicable, sidelights.
Rule 23
A vessel towing astern — what does she add, and when a third masthead light?
A yellow towing light above her stern light, and two masthead lights in a vertical line — three if the length of the tow measured from the stern of the towing vessel to the after end of the tow exceeds 200 m.
Rule 24
What does a towed vessel show, and what if the tow exceeds 200 m?
Sidelights and a stern light. If the tow exceeds 200 m, also a diamond shape by day (an all-round white light where prescribed).
Rule 24
What lights may a sailing vessel show in place of, or in addition to, the standard set?
Sidelights and stern light may be combined in a single lantern at or near the masthead. She may additionally carry two all-round lights at the masthead, red over green — but not together with the combined lantern.
Rule 25
A sailing vessel or vessel under oars less than 7 m — what is the minimum?
If she cannot show the prescribed lights, she must have ready at hand an electric torch or lighted lantern showing a white light in sufficient time to prevent collision.
Rule 25
Trawling versus other fishing — which lights?
Trawling: green over white. Other fishing: red over white. Add sidelights and stern light when making way through the water.
Rule 26
A fishing vessel with gear extending more than 150 m — what does she add?
An all-round white light in the direction of the outlying gear.
Rule 26
Lights and day shapes for a vessel not under command.
Two all-round red lights in a vertical line; by day, two balls in a vertical line. Sidelights and stern light are added when making way — but never masthead lights.
Rule 27
Lights and day shapes for a vessel restricted in her ability to maneuver.
Three all-round lights in a vertical line, red–white–red; by day, ball–diamond–ball. Masthead lights, sidelights, and stern light are added when making way.
Rule 27
How does a dredge show which side to pass?
RAM lights and shapes plus, on the obstructed side, two all-round red lights or two balls; on the clear side, two all-round green lights or two diamonds. Pass on the green side.
Rule 27
What marks a vessel engaged in diving operations?
RAM lights and shapes, plus a rigid replica of the International Code flag "A" not less than 1 m in height.
Rule 27
What may a vessel constrained by her draft show?
In addition to her power-driven lights: three all-round red lights in a vertical line, or a cylinder by day.
Rule 28
What lights identify a pilot vessel on duty?
Two all-round lights at or near the masthead in a vertical line, white over red. Underway she adds sidelights and stern light; at anchor, the anchor lights as well.
Rule 29
What does a vessel at anchor show?
Forward, an all-round white light or a ball; at or near the stern and lower, a second all-round white light. Under 50 m she may show one all-round white light where it is best seen.
Rule 30
What does a vessel aground show?
Her anchor lights, plus two all-round red lights in a vertical line — or three balls in a vertical line by day.
Rule 30
Sound & Light Signals
Rules 32–36 · 14 cards
How long is a short blast? A prolonged blast?
Short: about one second. Prolonged: four to six seconds.
Rule 32
Sound-signal equipment by vessel length (International).
100 m or more: whistle, bell, and gong. 12 m to 100 m: whistle and bell. Under 12 m: any means of making an efficient sound signal. Inland sets the bell threshold at 20 m, not 12 m.
Rule 33
The maneuvering whistle signals for vessels in sight of one another.
One short: I am altering course to starboard. Two short: I am altering course to port. Three short: my engines are going astern.
Rule 34
What is the danger signal?
Five or more short and rapid blasts — "I do not understand your intentions" or "I doubt you are taking sufficient action to avoid collision." It may be supplemented by five or more short rapid light flashes.
Rule 34
International Rule 34(c): how do you signal an intention to overtake?
Two prolonged + one short = "I intend to overtake you on your starboard side." Two prolonged + two short = "on your port side." The vessel being overtaken agrees with one prolonged, one short, one prolonged, one short. (The Inland overtaking signal is completely different — see the Inland deck.)
Rule 34
What signal do you sound approaching a blind bend?
One prolonged blast, when nearing a bend or an area of channel where other vessels may be obscured. Any approaching vessel within earshot answers with one prolonged blast.
Rule 34
Fog signal: power-driven vessel making way.
One prolonged blast at intervals of not more than 2 minutes.
Rule 35
Fog signal: power-driven vessel underway but stopped and making no way.
Two prolonged blasts about two seconds apart, at intervals of not more than 2 minutes.
Rule 35
Which vessels all sound one prolonged + two short in fog?
Not under command, restricted in ability to maneuver, constrained by draft, sailing, engaged in fishing, and towing or pushing — every one of them, at intervals of not more than 2 minutes.
Rule 35
Fog signal: vessel at anchor.
Rapid ringing of the bell for about 5 seconds, at intervals of not more than 1 minute. At 100 m or more, the bell is sounded forward and a gong is then sounded for 5 seconds aft.
Rule 35
Fog signal: vessel aground.
The bell signal for a vessel at anchor, plus three separate and distinct strokes of the bell immediately before and after it.
Rule 35
Fog signal: last manned vessel of a tow.
One prolonged followed by three short blasts, sounded immediately after the towing vessel's signal where practicable.
Rule 35
What are the limits on signals to attract attention?
The signal must not be capable of being mistaken for any signal authorized elsewhere in the Rules, and must be made so as not to embarrass any vessel. You may direct a searchlight toward the danger. Any attention light must not be mistakable for an aid to navigation, and high-intensity intermittent or revolving lights (strobes) shall be avoided.
Rule 36
Memory aid for fog signals.
One prolonged = making way under power. Two prolonged = stopped. One prolonged + two short = everything else — NUC, RAM, constrained by draft, sailing, fishing, towing.
Rule 35
Distress & Exemptions
Rules 37–38 · 4 cards
Name six recognized distress signals.
A gun or explosive at about 1-minute intervals; continuous sounding of a fog-signal apparatus; rockets or shells throwing red stars; MAYDAY by radiotelephone (VHF channel 16); the orange smoke signal; slowly and repeatedly raising and lowering outstretched arms; an activated EPIRB; flames on the vessel; an orange flag with a black square and ball; dye marker; the square shape with a ball above or below; a high-intensity white light at 50–70 flashes per minute.
Rule 37
Which distress signal is a hand signal, requiring no equipment at all?
Slowly and repeatedly raising and lowering outstretched arms to each side.
Rule 37
Which flag combination signals distress?
A square flag with a ball above or below it — or the Code flags N over C.
Rule 37
Who can be exempted from the lights, shapes, and sound-equipment rules?
Vessels built (or, for lights and shapes, fitted) before the Rules entered into force in 1977, where compliance would require retrofitting that is not readily practicable. Exemptions carry stated time limits, apply only to the extent structural change would be required, and must be logged and reported.
Rule 38
Inland vs. International
33 CFR 83 · 21 cards
Where do the Inland Rules apply?
Shoreward of the COLREGS Demarcation Lines — on U.S. inland waters, the Great Lakes, and the Western Rivers. Seaward of those lines the International Rules apply. The lines are charted, and they are the only thing that decides which regime you are under.
Rule 1
What are the "Western Rivers" under the Inland Rules?
The Mississippi River and its tributaries, South Pass and Southwest Pass to the demarcation lines, the Port Allen–Morgan City Alternate Route, and the Atchafalaya River above its junction with that route, including the Old River and the Red River. Several Inland rules apply only there (and on the Great Lakes).
Rule 3
Great Lakes or Western Rivers: who has right of way, upbound or downbound?
The downbound vessel — the one running with a following current — has the right of way. She proposes the manner and place of passage and initiates the maneuvering signals. The upbound vessel holds as necessary to permit safe passing. This overrides both the keep-right rule and Rule 14.
Rule 9
Inland Rule 15(b): crossing a river on the Great Lakes or Western Rivers.
A power-driven vessel crossing a river shall keep out of the way of a power-driven vessel ascending or descending the river — regardless of which side she is on. The ordinary crossing rule does not decide it.
Rule 15
Which Rule 18 category does NOT exist in the Inland Rules?
Vessel constrained by her draft. Inland Rule 18(d) is simply [Reserved], and Inland Rule 28 (her lights) is Reserved too. The category, its definition, and its three all-round red lights are International only.
Rule 18
Inland sound-signal equipment thresholds.
12 m or more: whistle. 20 m or more: bell as well. 100 m or more: gong in addition. The bell threshold is the trap — International requires it from 12 m, Inland from 20 m.
Rule 33
What do one and two short blasts mean under the INLAND Rules?
One short: "I intend to leave you on my port side." Two short: "I intend to leave you on my starboard side." Three short: "I am operating astern propulsion." These state an intention — International states an action already being taken.
Rule 34
When do the Inland maneuvering signals apply?
When power-driven vessels are in sight of one another and meeting or crossing within half a mile of each other. The International rule has no distance limit and no agreement requirement.
Rule 34
Under Inland Rules, what does the other vessel do when it hears your one-blast signal?
If she agrees, she sounds the same signal back and takes the steps needed for safe passing. If she doubts the safety of the proposal she sounds the danger signal (five or more short rapid blasts), and both vessels take precautionary action until a safe passing agreement is made.
Rule 34
The Inland overtaking signals.
One short = "I intend to overtake you on your starboard side." Two short = "on your port side." The vessel being overtaken sounds a similar signal if she agrees, or the danger signal if in doubt. Not the International two-prolonged-plus-short signals.
Rule 34
Inland only: what signal does a vessel sound when leaving a dock or berth?
One prolonged blast. There is no such requirement in the International Rules.
Rule 34
Inland only: can a radiotelephone agreement replace the whistle signals?
Yes. A vessel that reaches agreement in a head-on, crossing, or overtaking situation — for example by VHF under the Vessel Bridge-to-Bridge Radiotelephone Act — is not obliged to sound the whistle signals, though she may. If agreement is not reached, whistle signals shall be exchanged in a timely manner and shall prevail.
Rule 34
Inland light signals supplementing the whistle — what color and range?
An all-round white or yellow light, visible at least 2 miles, synchronized with the whistle, each flash about 1 second. International specifies an all-round white light visible at least 5 miles.
Rule 34
What is a "special flashing light," and which regime has it?
Inland only. A yellow light flashing at 50 to 70 flashes per minute, placed as far forward as practicable on the centerline of the tow, showing over an arc of not less than 180° nor more than 225° — from right ahead to no more than 22.5° abaft the beam on either side.
Rule 21
Which vessels carry the special flashing light?
A vessel being pushed ahead (not part of a composite unit) shows sidelights and a special flashing light at the forward end. A vessel towed alongside shows a sternlight and, at the forward end, sidelights and a special flashing light.
Rule 24
Inland only: the special anchorage area exemption for anchor lights.
A vessel of less than 20 m at anchor in a special anchorage area designated by the Coast Guard need not exhibit anchor lights or shapes. (The general Rule 30 exemption, in both regimes, is for vessels under 7 m away from a channel, fairway, anchorage, or where vessels normally navigate.)
Rule 30
Inland only: which moored barges must be lit, and with what?
Barges projecting into a buoyed or restricted channel; barges moored so as to reduce the navigable width to under 80 m; barges moored in groups more than two wide or over 25 m wide; and any barge not moored parallel to the bank or dock. Each shows two all-round white lights visible at least 1 nautical mile.
Rule 30
Inland only: who is excused from the anchored-vessel fog bell in a special anchorage?
A vessel of less than 20 m, and a barge, canal boat, scow, or other nondescript craft, when anchored in a Coast Guard–designated special anchorage area.
Rule 35
A 15 m vessel at anchor in fog under the Inland Rules — what must she sound?
She is not obliged to give the bell signal (that duty starts at 20 m), but if she does not, she must make some other efficient sound signal at intervals of not more than 2 minutes. The same applies to vessels under 12 m.
Rule 35
How does Inland Rule 36 differ from International Rule 36?
Both allow signals that cannot be mistaken for an authorized signal, and both allow directing a searchlight toward the danger without embarrassing any vessel. The International rule adds two sentences the Inland rule does not have: the light must not be mistakable for an aid to navigation, and strobes shall be avoided.
Rule 36
Air-cushion vessel in non-displacement mode — what light, and in which regime?
An all-round flashing yellow light, in both regimes. Inland adds "where it can best be seen." A WIG craft taking off, landing, or in flight near the surface shows a high-intensity all-round flashing red light in both.
Rule 23
Study aid only — it certifies nothing. Content is checked against the U.S. Coast Guard Navigation Rules and Regulations Handbook (corrected 12 August 2024), covering the 72 COLREGS as amended through IMO Resolution A.1085(28) and the Inland Rules at 33 CFR Part 83. The governing text is the handbook, not this page. Read it at the USCG Navigation Center.