Free interactive quiz
Ten simplified night views. Practise recognising light arrangements, then read the rule and the limits of what the lights tell you.
10 questions · about 6 min · no sign-up · Updated
These are simplified examples with prescribed lights assumed visible as stated. At sea, a light can be obscured, out of range or confused with a shore light or mark. Identify the full pattern and keep observing: light colour alone does not establish tack, exact course, speed or collision risk.
Two habits solve most of these: look for a white masthead light (power-driven, not sail), then look for vertical all-round lights above the deck (a vessel's status: not under command, restricted, fishing, pilot, towing).
Want to learn it first? Navigation lights: how to identify a vessel at night.
10 questions
Question 1 of 10
Answer: A power-driven vessel heading towards you
This illustrates a power-driven vessel’s bow-on aspect: green to your left, red to your right, with a white masthead light. A sailing vessel under sail alone shows no masthead light. International Rule 14 applies when both vessels are power-driven, in sight and meeting on reciprocal or nearly reciprocal courses with risk of collision; then both alter to starboard.
COLREGs Rules 21, 23 and 14
Answer: A power-driven vessel, showing you her starboard side
The green sidelight identifies the vessel’s starboard aspect and the masthead light indicates a power-driven vessel. This does not establish her exact heading, speed or track across your view. Determine collision risk and the complete encounter before assigning responsibilities; Rule 15 needs two power-driven vessels in sight crossing with risk of collision.
COLREGs Rules 21 and 23
Answer: A sailing vessel under sail, showing you her port side
The basic sailing-vessel arrangement is sidelights and a sternlight, without a masthead light (Rule 25(a)). From the port side, only the red sidelight is in view. At sea, a lone red light does not prove this identification: other lights may be obscured or out of range, and it might be a navigation mark. It does not establish sailing tack.
COLREGs Rule 25(a)
Answer: You are seeing the stern light of a vessel ahead — you are in her overtaking sector
The sternlight is white and covers 135° centred astern (Rule 21(c)). If you are overtaking, Rule 13 requires you to keep clear until past and clear. Without the stated aspect, one white light is ambiguous: it could be an anchor light or another small-craft arrangement. Range change alone does not establish whether a vessel is anchored.
COLREGs Rules 21(c), 13 and 30
Answer: A vessel not under command, making way
Two all-round red lights in a vertical line mean a vessel not under command (Rule 27(a)) — unable to manoeuvre through some exceptional circumstance. The sidelight tells you she is making way through the water; a NUC vessel not making way shows only the two reds. A vessel aground would add anchor lights (white) to the two reds; constrained by draught is three reds.
COLREGs Rule 27(a)
Answer: A vessel restricted in her ability to manoeuvre, making way
Red-white-red in a vertical line is a vessel restricted in her ability to manoeuvre (Rule 27(b)) — dredging, cable laying, diving operations and the like. When making way she also shows her masthead light, sidelights and stern light, which is why you can see the masthead light and a sidelight. Rule 18 tells sailing and power-driven vessels to keep out of her way.
COLREGs Rule 27(b)
Answer: Trawling, and making way
Green over white all-round lights identify trawling (Rule 26(b)); sidelights and sternlight are added when making way. Red over white identifies fishing other than trawling. Rule 18 specifies responsibilities towards fishing vessels, subject to Rules 9, 10 and 13; it is not a universal ranking.
COLREGs Rule 26(b)
Answer: Fishing other than trawling, not making way through the water
Red over white all-round lights mean a vessel engaged in fishing other than trawling (Rule 26(c)) — nets, lines or other gear that may extend some way from her. With no sidelights or stern light showing she is not making way through the water. Trawlers show green over white. Keep well clear: her gear may extend more than 150 metres, in which case she shows an extra all-round white light in its direction.
COLREGs Rule 26(c)
Answer: A vessel towing, with a tow of 200 metres or less, showing you her starboard side
Two masthead lights in a vertical line are the mark of a towing vessel with a tow of 200 metres or less (Rule 24(a)); three in a vertical line mean a tow over 200 metres. A power-driven vessel of 50 metres or more also shows two masthead lights, but the after one is higher and well aft of the forward one — from abeam they are separated horizontally, not stacked. The green sidelight tells you she is showing you her starboard side. Look for the tow astern of her.
COLREGs Rule 24(a)
Answer: A pilot vessel on pilotage duty, under way and heading towards you
White over red all-round lights at or near the masthead mean a vessel engaged on pilotage duty (Rule 29(a)). When under way she also shows sidelights and a stern light — and seeing both sidelights, green to your left and red to your right, means she is heading towards you. A sailing vessel's optional lights are red over green (Rule 25(c)), the other way round and with no masthead light.
COLREGs Rule 29(a)
The guides behind these questions — each one sourced, diagrammed and checked against the rule text.
COLREGs
Masthead, sidelights and sternlight and their arcs, then the extra lights that tell you a vessel is fishing, towing, anchored, not under command or restricted — with diagrams for each and the rules they come from.
12 min read
COLREGs
Sail vs sail, power vs power, overtaking, head-on and crossing: what COLREG Rules 12–18 actually require of the give-way and stand-on vessel, with diagrams and a reasoning sequence you can use in the exam and at sea.
12 min read
COLREGs
When Rule 19 applies to vessels not in sight in or near restricted visibility, safe speed, radar-only contacts and Rule 35 fog signals explained.
9 min read
Questions and explanations were checked against the documents below on . Scope: International COLREGs, Part C (Rules 21–30) · Vessels under way unless stated · Letters label each light so colour never carries the meaning alone. Rules, buoyage and syllabuses change and can differ by jurisdiction — the official text always takes precedence.
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The Day Skipper Theory, Actually Explained course covers Navigation Lights and Shapes — every answer explained, with spaced review that brings back what you miss. Free to download, no account, works offline. One full quiz and 3 Daily Challenge rounds a day on the free plan.
