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30

Anchored Vessels and Vessels Aground

A vessel under 50 m at anchor may show one all-round white light where best seen instead of two anchor lights. By day it shows a ball in the forepart.

Rule 30 prescribes lights and shapes for anchored vessels and vessels aground.

a
A vessel at anchor shall exhibit where it can best be seen:
  • 1in the fore part, an all-round white light or one ball;
  • 2at or near the stern and at a lower level than the forward light, another all-round white light.
b
A vessel of less than 50 metres in length may exhibit an all-round white light where it can best be seen instead of the lights prescribed in paragraph (a).
c
A vessel at anchor may, and a vessel of 100 metres or 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) and in addition, where they can best be seen:
  • 1two all-round red lights in a vertical line;
  • 2three balls in a vertical line.
e
A vessel of less than 7 metres 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).
f
A vessel of less than 12 metres in length, when aground, shall not be required to exhibit the lights or shapes prescribed in sub-paragraphs (d)
  • 1and
  • 2.
Vessel at anchor ≥ 50 m — white forward + white aft (lower).
Aground example using one anchor light: add two red all-round lights; by day, show three balls vertically. Vessels under 12 m need not show these additional aground signals.

IMO COLREG 1972Official text

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.
Source:

An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.

Recognition Sequence

Classify the vessel state first: underway, making way, stopped, at anchor, aground, towing, fishing, pilotage or special condition.

Read special lights vertically from top to bottom before using sidelights and sternlight to confirm aspect.

Use the complete display and any vessel length stated in the scenario.

Optional second masthead lights, two anchor lights or deck illumination do not by themselves prove a minimum vessel length.

Exam Focus

Avoid identifying a vessel from one colour alone.

Many mistakes come from spotting a red light and guessing before checking the full pattern.

If the question mentions 'making way', 'underway but stopped', 'at anchor' or 'aground', that wording usually determines which extra lights or shapes appear.

Key Takeaways

1

Anchored vessels show a forward all-round white light + a lower one aft (≥50m); <50m may show a single all-round white

2

The anchor day shape is one black ball, exhibited forward

3

Aground = anchor signals PLUS two red lights vertically (night) and three balls vertically (day)

4

≥100m at anchor must illuminate decks; smaller vessels may do so

5

A vessel under 7 metres at anchor needs no anchor signals only away from narrow channels, fairways, anchorages and places where other vessels normally navigate

6

<12m vessel aground: no need to show the two-red and three-balls aground signals (but anchor lights still required if applicable)

Common Mistakes

Showing only the aground red lights and forgetting the anchor signals

Forgetting the anchor ball by day

Assuming small craft never need anchor lights in navigated waters

Forgetting that a <12m vessel aground is exempt from the aground signals but still has anchor obligations

Test Your Knowledge

Practise this topic and review the explanation for each answer.

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Frequently asked questions about COLREG Rule 30

What lights does a vessel at anchor show?

An all-round white light or one ball in the fore part, and at or near the stern, at a lower level, another all-round white light (Rule 30(a)). A vessel of less than 50 metres may instead exhibit one all-round white light where it can best be seen.

What lights and shapes does a vessel aground show?

The anchor lights of Rule 30(a) or (b) plus two all-round red lights in a vertical line, and by day three balls in a vertical line (Rule 30(d)). A vessel of less than 12 metres aground is not required to exhibit those aground signals.

Which anchored vessels must illuminate their decks?

A vessel of 100 metres or more in length shall use her available working or equivalent lights to illuminate her decks; a smaller vessel at anchor may do so (Rule 30(c)).