Rule 24 distinguishes towing astern, towing alongside and pushing.
a
A power-driven vessel towing astern shows two masthead lights vertically instead of the Rule 23(a)
- 1or
- 2masthead light. If tow length exceeds 200 metres, measured from the towing vessel's stern to the after end of the tow, she shows three vertically. She also shows sidelights, a sternlight and a yellow towing light vertically above the sternlight; a diamond shape is required if the tow exceeds 200 metres.
b
A rigidly connected pushing vessel and vessel pushed ahead form a composite unit and show Rule 23 power-driven-vessel lights.
c
A power-driven vessel pushing ahead or towing alongside, except as a composite unit, shows two masthead lights vertically, sidelights and a sternlight.
d
A towing or pushing vessel under (a) or (c) also meets Rule 23(a)
- 2: the second masthead light abaft and higher is required at 50 metres or more.
e
A vessel or object towed astern, except the special cases in (g), shows sidelights and a sternlight; if the tow exceeds 200 metres, also a diamond shape.
f
Pushed or alongside-towed groups are lit as one vessel. A vessel pushed ahead, other than in a composite unit, shows sidelights at the forward end; an alongside tow shows a sternlight and sidelights at the forward end.
g
Inconspicuous partly submerged tows have special all-round white-light and diamond arrangements, with additional lights according to width and length; consult the full source wording below.
h
If a tow cannot practically show the prescribed lights or shapes, take all possible measures to light it or indicate its presence.
i
The limited exception for a vessel not normally towing while assisting a vessel in distress does not remove the duty to indicate the towing relationship as far as possible, in particular by illuminating the towline under Rule 36.
IMO COLREG 1972Official text
Full wording of the rule, reproduced from the official source below.
(a) A power-driven vessel when towing shall exhibit:
(i) instead of the light prescribed in Rule 23(a)(i) or (a)(ii), two masthead lights in a vertical line. When the length of the tow, measuring from the stern of the towing vessel to the after end of the tow, exceeds 200 meters, three such lights in a vertical line;
(ii) sidelights;
(iii) a sternlight;
(iv) a towing light in a vertical line above the sternlight; and
(v) when the length of the tow exceeds 200 meters, a diamond shape where it can best be seen.
(b) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and exhibit the lights prescribed in Rule 23.
(c) A power-driven vessel when pushing ahead or towing alongside, except in the case of a composite unit, shall exhibit:
(i) instead of the light prescribed in Rule 23(a)(i) or 23(a)(ii), two masthead lights in a vertical line;
(ii) sidelights; and
(iii) a sternlight.
(d) A power-driven vessel to which paragraph (a) or (c) of this Rule applies shall also comply with Rule 23(a)(ii).
(e) A vessel or object being towed, other than those mentioned in paragraph (g) of this Rule, shall exhibit:
(i) sidelights;
(ii) a sternlight;
(iii) when the length of the tow exceeds 200 meters, a diamond shape where it can best be seen.
(f) Provided that any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel:
(i) a vessel being pushed ahead, not being part of a composite unit, shall exhibit at the forward end, sidelights;
(ii) a vessel being towed alongside shall exhibit a sternlight and at the forward end, sidelights.
(g) An inconspicuous, partly submerged vessel or object, or combination of such vessels or objects being towed, shall exhibit:
(i) if it is less than 25 meters in breadth, one all-round white light at or near the forward end and one at or near the after end except that dracones need not exhibit a light at or near the forward end;
(ii) if it is 25 meters or more in breadth, two additional all-round white lights at or near the extremities of its breadth;
(iii) if it exceeds 100 meters in length, additional all-round white lights between the lights prescribed in subparagraphs (i) and (ii) so that the distance between the lights shall not exceed 100 meters;
(iv) a diamond shape at or near the aftermost extremity of the last vessel or object being towed and if the length of the tow exceeds 200 meters an additional diamond shape where it can best be seen and located as far forward as is practicable.
(h) Where from any sufficient cause it is impracticable for a vessel or object being towed to exhibit the lights or shapes prescribed in paragraph (e) or (g) of this Rule, all possible measures shall be taken to light the vessel or object towed or at least to indicate the presence of such vessel or object.
(i) Where from any sufficient cause it is impracticable for a vessel not normally engaged in towing operations to display the lights prescribed in paragraph (a) or (c) of this Rule, such vessel shall not be required to exhibit those lights when engaged in towing another vessel in distress or otherwise in need of assistance. All possible measures shall be taken to indicate the nature of the relationship between the towing vessel and the vessel being towed as authorized by Rule 36, in particular by illuminating the towline.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
Two masthead lights for normal tow, three if tow exceeds 200m
2
Yellow towing light shown above the sternlight
3
Diamond day shape if tow exceeds 200m
4
Composite units (rigidly connected) treated as one power-driven vessel
Common Mistakes
Not showing three masthead lights when tow exceeds 200m
Forgetting the diamond day shape for long tows
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More rules in this Part
- Definitions (Lights)Defines masthead light, sidelights, sternlight, towing light, all-round light and flashing light.
- Visibility of LightsSpecifies minimum visibility ranges for lights based on vessel length.
- Fishing VesselsFishing vessels show green over white when trawling, red over white for other fishing, and sidelights plus sternlight when making way.
- Vessels Not Under Command or Restricted in Ability to ManoeuvreNUC shows two red all-round lights vertically. RAM shows red-white-red all-round lights vertically.
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