1The rule in plain words
In one sentence…
A vessel aground shows her anchor lights plus two all-round red lights at night; by day, three balls in a vertical line.
What does an anchored vessel show?
In the fore part, an all-round white light or, by day, one ball; at or near the stern, another at a lower level. The stern light is at a lower level than the forward light.
What changes with length?
A vessel of less than 50 metres may show one all-round white light instead of paragraph (a)'s lights. Working or equivalent lights must illuminate her decks if she is 100 metres and more.
How do you recognise a vessel aground?
It shows the anchor lights and, in addition, displays two all-round red lights in a vertical line and three balls in a vertical line.
When are there exemptions?
Less than 7 metres at anchor, not in or near a narrow channel, fairway, anchorage or where vessels normally navigate: no lights or shape from (a) or (b). A vessel aground of less than 12 metres need not show (d)(i) or (ii).
2See it in 3D
Turn the vessel or pick bow, stern, port or starboard: this is how her lights look at night.
An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.
3Key points
- 1.
At anchor → fore part and stern · stern light lower.
- 2.
50 metres and 100 metres → permitted substitute · deck illumination required.
- 3.
Aground = anchor lights + two reds (night) · three balls (day).
- 4.
Separate exemptions: less than 7 metres anchored · less than 12 metres aground.
4Frequent mistakes
Wrong: "Any anchored vessel can use one white light."
Right: Only a vessel less than 50 metres may use one all-round white light instead of paragraph (a)'s lights.
Wrong: "Aground means two red lights only."
Right: Aground also requires three balls in a vertical line, in addition to the anchor lights.
Wrong: "A vessel exactly 7 metres at anchor is exempt."
Right: The exemption is for less than 7 metres and only in the stated locations.
5Exam keys & interpretation
Exam keys
"Less than 50 metres" permits one white light; "100 metres and more" requires deck illumination.
"In addition" for aground means keep the anchor lights and add two red lights and three balls.
Separate "less than 7 metres" at anchor from "less than 12 metres" aground; their exemptions are not interchangeable.
How to read it
First identify anchored or aground; then check the vessel's length and location before applying an exemption.
"In addition" means grounding doesn't remove the anchor lights: add two reds; by day, three balls.
6Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
(a) A vessel at anchor shall exhibit where it can best be seen:
(i) in the fore part, an all-round white light or one ball;
(ii) at or near the stern and at a lower level than the light prescribed in subparagraph (i), an all-round white light.
(b) A vessel of less than 50 meters in length may exhibit an all-round white light where it can best be seen instead of the lights prescribed in paragraph (a) of this Rule.
(c) A vessel at anchor may, and a vessel of 100 meters and more in length shall, also use the available working or equivalent lights to illuminate her decks.
(d) A vessel aground shall exhibit the lights prescribed in paragraph (a) or (b) of this Rule and in addition, where they can best be seen:
(i) two all-round red lights in a vertical line;
(ii) three balls in a vertical line.
(e) A vessel of less than 7 meters in length, when at anchor, not in or near a narrow channel, fairway or anchorage, or where other vessels normally navigate, shall not be required to exhibit the lights or shape prescribed in paragraphs (a) and (b) of this Rule.
(f) A vessel of less than 12 meters in length, when aground, shall not be required to exhibit the lights or shapes prescribed in subparagraphs (d)(i) and (ii) of this Rule.7Test your knowledge
What lights correspond to a vessel at anchor?
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