What lights does a vessel not under command show?

Two all-round red lights in a vertical line where they can best be seen, plus sidelights and a sternlight when making way (Rule 27(a)). By day a not-under-command vessel shows two balls in a vertical line.

What lights does a vessel restricted in her ability to manoeuvre show?

Three all-round lights in a vertical line — the highest and lowest red and the middle one white — plus masthead lights, sidelights and a sternlight when making way (Rule 27(b)). Her day shape is ball-diamond-ball. This standard RAM pattern excludes mineclearance; vessels under 12 metres, except those engaged in diving, need not display Rule 27 signals.

How do you tell NUC lights from RAM lights?

A vessel not under command shows red over red; a vessel restricted in her ability to manoeuvre shows red-white-red. By day the difference is two balls against ball-diamond-ball, and both show sidelights and a sternlight only when making way.

What extra lights does a dredging or underwater-operations vessel show?

When restricted in her ability to manoeuvre she additionally shows two red all-round lights or two balls on the obstructed side, and two green all-round lights or two diamonds on the side available for passing (Rule 27(d)).

Vessels Not Under Command or Restricted in Ability to Manoeuvre

A vessel not under command shows two red all-round lights or, by day, two balls. This example makes no way. Its lights also apply in daytime restricted visibility.

Rule 27 covers NUC and RAM vessels and specific operations.

NUC: two all-round red lights vertically; by day, two balls vertically. When making way, add sidelights and a sternlight.

RAM, other than mineclearance: red-white-red all-round lights; by day, ball-diamond-ball. When making way, add masthead light(s), sidelights and a sternlight. At anchor, add Rule 30 anchor signals, except for dredging/underwater-operation provisions in (d).

A towing operation that severely restricts the towing vessel and tow from deviating from course requires Rule 24(a) lights plus the RAM status lights and shapes.

RAM dredging or underwater operations: where an obstruction exists, show two red lights or balls on the obstructed side and two green lights or diamonds on the passing side. At anchor, use the signals in this paragraph instead of Rule 30 anchor signals.

A diving vessel too small to show all the (d) arrangements shows red-white-red lights and a rigid International Code flag A, at least 1 metre high, visible all round.

A mineclearance vessel shows three all-round green lights or three balls in addition to Rule 23 lights or appropriate Rule 30 anchor signals. These indicate danger to another vessel approaching within 1,000 metres.

Vessels below 12 metres, except those engaged in diving operations, need not show this rule's lights and shapes.

These signals are not distress signals; Annex IV contains distress signals.

Schematic identification detail; other required lights are not shown. A vessel restricted by its work and making way shows red-white-red, masthead light(s), sidelights and sternlight; by day, ball-diamond-ball. Rule 27(b) arrangement; mineclearance uses Rule 27(f).

Day-shape example. A working dredger marks the obstructed side with two red lights or two balls and the passable side with two green lights or two diamonds, in addition to its restricted-manoeuvrability signals and applicable navigation lights. Assess available depth and clearance before passing.

Identification detail. Mineclearance identification: three green all-round lights or three balls, additional to applicable navigation or anchor lights. Approaching within 1,000 m is dangerous.

IMO COLREG 1972Official text

Full wording of the rule, reproduced from the official source below.

(a) A vessel not under command shall exhibit: (i) two all-round red lights in a vertical line where they can best be seen; (ii) two balls or similar shapes in a vertical line where they can best be seen; (iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight. (b) A vessel restricted in her ability to maneuver, except a vessel engaged in mine clearance operations, shall exhibit: (i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; (ii) three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond; (iii) when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in subparagraph (i); (iv) when at anchor, in addition to the lights or shapes prescribed in subparagraphs (i) and (ii), the light, lights or shape prescribed in Rule 30. (c) A power-driven vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shall, in addition to the lights or shapes prescribed in Rule 24(a), exhibit the lights or shapes prescribed in subparagraphs (b)(i) and (ii) of this Rule. (d) A vessel engaged in dredging or underwater operations, when restricted in her ability to maneuver, shall exhibit the lights and shapes prescribed in subparagraphs (b)(i), (ii) and (iii) of this Rule and shall in addition, when an obstruction exists, exhibit: (i) two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists; (ii) two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass; (iii) when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30. (e) Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in paragraph (d) of this Rule, the following shall be exhibited: (i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; (ii) a rigid replica of the International Code flag “A” not less than 1 meter in height. Measures shall be taken to ensure its all-round visibility. (f) A vessel engaged in mine clearance operations shall, in addition to the lights prescribed for a power-driven vessel in Rule 23 or to the lights or shape prescribed for a vessel at anchor in Rule 30 as appropriate, exhibit three all-round green lights or three balls. One of these lights or shapes shall be exhibited near the foremast head and one at each end of the fore yard. These lights or shapes indicate that it is dangerous for another vessel to approach within 1000 meters of the mine clearance vessel. (g) Vessels of less than 12 meters in length, except those engaged in diving operations, shall not be required to exhibit the lights and shapes prescribed in this Rule. (h) The signals prescribed in this Rule are not signals of vessels in distress and requiring assistance. Such signals are contained in Annex IV to these Regulations.

Source:

U.S. Coast Guard — International Navigation Rules (2024)

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

NUC normally shows red-red and two balls; standard RAM shows red-white-red and ball-diamond-ball

Standard RAM lights do not describe mineclearance; mineclearance has three green lights or balls

Dredging/underwater obstruction: red or balls on the obstructed side, green or diamonds on the available side

Small diving vessels may need red-white-red and a rigid Code flag A at least 1 metre high

Below 12 metres the Rule 27 signals are optional except for diving operations

Common Mistakes

Confusing NUC lights (red-red) with RAM lights (red-white-red)

Forgetting that NUC and RAM only show sidelights when making way

Test Your Knowledge

Practise this topic and review the explanation for each answer.

Last reviewed: September 9, 2026