Vessels Not Under Command or Restricted in Their Ability to Maneuver

Rule text#

(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; and

(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 paragraph (b)(i) of this Rule; and

(iv)When at anchor, in addition to the lights or shapes prescribed in paragraphs (b)(i) and (ii) of this Rule, the light, lights or shapes prescribed in Rule 30 (§ 83.30).

(c)A vessel engaged in a towing operation which 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 paragraphs (b)(i) and (ii) of this Rule, exhibit the lights or shapes prescribed in Rule 24 (§ 83.24).

(d)A vessel engaged in dredging or underwater operations, when restricted in her ability to maneuver, shall exhibit the lights and shapes prescribed in paragraphs (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; and

(iii)When at anchor, the lights or shapes prescribed by this paragraph, instead of the lights or shape prescribed in Rule 30 (§ 83.30).

(iv)Dredge pipelines that are floating or supported on trestles shall display the following lights at night and in periods of restricted visibility.

(1)One row of yellow lights. The lights must be:

(A)Flashing 50 to 70 times per minute,

(B)Visible all round the horizon,

(C)Visible for at least 2 miles,

(D)Not less than 1 and not more than 3.5 meters above the water,

(E)Approximately equally spaced, and

(F)Not more than 10 meters apart where the pipeline crosses a navigable channel. Where the pipeline does not cross a navigable channel the lights must be sufficient in number to clearly show the pipeline's length and course.

(2)Two red lights at each end of the pipeline, including the ends in a channel where the pipeline is separated to allow vessels to pass (whether open or closed). The lights must be:

(A)Visible all round the horizon, and

(B)Visible for at least 2 miles, and

(C)One meter apart in a vertical line with the lower light at the same height above the water as the flashing yellow light.

(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, as appropriate, the following shall instead 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 (§ 83.23) or to the lights or shape prescribed for a vessel at anchor in Rule 30 (§ 83.30), 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)A vessel of less than 12 meters in length, except when engaged in diving operations, is not required to exhibit the lights or 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 Rules (33 CFR part 87). [USCG-2012-0102, 79 FR 37912, July 2, 2014, as amended by USCG-2012-0102, 79 FR 68622, Nov. 18, 2014; USCG-2018-0874, 84 FR 30878, June 28, 2019]

Why it shows up on the exam#

Learn the pair as opposites: two reds mean the vessel cannot manoeuvre at all, red-white-red means she can but must not be asked to. The asymmetric dredge signal is the other reliable question — two reds mark the side to stay away from, two greens the side you may pass, and candidates routinely reverse them. Note also that under 12 metres is exempt from Rule 27 entirely, except when engaged in diving operations.

Exam checkpoints#

1. 1.

   Not under command

   Two all-round reds · two balls

   Two all-round red lights in a vertical line where they can best be seen, and two balls or similar shapes in a vertical line by day. When making way through the water she adds sidelights and a sternlight; when not making way she shows the reds or balls alone.

2. 2.

   Restricted in ability

   Red-white-red · ball-diamond-ball

   Three all-round lights in a vertical line — red, white, red — and by day three shapes in a vertical line: ball, diamond, ball. When underway she also shows masthead lights, sidelights and a sternlight; at anchor she adds the Rule 30 anchor lights.

3. 3.

   Dredging / underwater work

   Two reds = obstruction

   In addition to the restricted signal: two all-round red lights or two balls in a vertical line on the side where the obstruction exists, and two all-round green lights or two diamonds on the side on which another vessel may pass. Red is the side to avoid.

4. 4.

   Diving operations

   Rigid flag A replica

   Where the size of a vessel engaged in diving operations makes the full signal impracticable, she shows three all-round lights in a vertical line — red, white, red — and a rigid replica of the International Code flag A. Diving is the one activity that keeps Rule 27 duties below 12 metres.

5. 5.

   Towing that severely restricts

   Restricted signal + Rule 24

   A vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shows the restricted-in-ability signal in addition to the towing lights required by Rule 24.

Where Inland differs#

Inland Rule 27 (33 CFR §83.27) matches COLREGs Rule 27 in its light and shape combinations, so the signatures memorised for one rulebook read the same in the other.

Rule 27 — common exam questions#

What is the difference between not under command and restricted in ability to manoeuvre?

Not under command means the vessel, through some exceptional circumstance, is unable to manoeuvre as the Rules require — a steering or engine failure, for instance — and she shows two all-round red lights in a vertical line. Restricted in her ability to manoeuvre means the nature of her work restricts her, so she can still steer but cannot readily keep out of the way; she shows red over white over red. Two reds: cannot. Red-white-red: can, but do not ask her to.

What lights does a dredge show?

The restricted-in-ability signal — red, white, red in a vertical line with ball, diamond, ball by day — plus an asymmetric pair marking the working side: two all-round red lights or two balls on the side where the obstruction exists, and two all-round green lights or two diamonds on the side another vessel may pass. Pass on the green side.

What shapes mean restricted in ability to manoeuvre?

Ball, diamond, ball in a vertical line, matching the red-white-red light signature at night. The diamond in the middle is the identifying element — a ball-diamond-ball hoist is nothing else in the rulebook.

Does Rule 27 apply to small vessels?

Mostly not. A vessel of less than 12 metres in length is not required to exhibit the lights or shapes prescribed in Rule 27, with one exception: when she is engaged in diving operations. That is why a small dive boat still displays the rigid flag A replica.

Is a vessel not under command the same as a vessel aground?

No. Aground has its own signal under Rule 30 — three balls in a vertical line by day, and anchor lights plus two all-round reds at night. Rule 27's two reds without anchor lights indicate a vessel underway but unable to manoeuvre, which is a different problem for anyone approaching her.

Authoritative source#

Source links checked against the current public rule corpus on 2026-07-26.

• 33 CFR §83.27 — the section this text comes from, with its neighbours.
• International COLREGs Rule 27 verbatim text is published by the IMO and is authoritative for international waters.

Practice this rule#

One real exam question on this rule, cited to source. No sign-up.