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25

Sailing Vessels Underway and Vessels Under Oars

Sailing vessel underway — sidelights + sternlight.

Rule 25 covers sailing vessels underway and vessels under oars.

a
A sailing vessel underway shows sidelights and a sternlight.
b
Below 20 metres, these lights may be combined in one lantern at or near the top of the mast where it can best be seen.
c
Optional red over green all-round lights may be shown near the mast top in addition to separate sidelights and sternlight. They must not be shown together with the combined lantern in (b). These all-round lights are not the defined white masthead light.
d
  • 1A sailing vessel below 7 metres shall, if practicable, show the (a) or (b) lights; otherwise she must have a white torch or lighted lantern ready to be shown in sufficient time to prevent collision.
  • 2A vessel under oars may show the sailing-vessel lights. If she does not, she must have a white torch or lighted lantern ready and show it in sufficient time to prevent collision.
e
A vessel under sail also being propelled by machinery must show a cone, apex downward, forward where it can best be seen. She is a power-driven vessel for the navigation and night-light rules.
Identification detail. A sailing vessel may add red-over-green all-round lights to its sidelights and sternlight. This pair must not be combined with the tricolour lantern.
A vessel under sail and also propelled by machinery is power-driven: it shows the corresponding lights and, by day, a cone with its apex downward.

IMO COLREG 1972Official text

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

(a) A sailing vessel underway shall exhibit: (i) sidelights; (ii) a sternlight. (b) In a sailing vessel of less than 20 meters in length the lights prescribed in paragraph (a) of this Rule may be combined in one lantern carried at or near the top of the mast where it can best be seen. (c) A sailing vessel underway may, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower green, but these lights shall not be exhibited in conjunction with the combined lantern permitted by paragraph (b) of this Rule. (d) (i) A sailing vessel of less than 7 meters in length shall, if practicable, exhibit the lights prescribed in paragraph (a) or (b) of this Rule, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision. (ii) A vessel under oars may exhibit the lights prescribed in this Rule for sailing vessels, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision. (e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards.
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

Sailing underway: sidelights and sternlight; below 20 metres a combined mast-top lantern is permitted

2

Optional red-over-green all-round lights cannot be used with the combined tricolour lantern

3

Below 7 metres, the white-light alternative applies only if showing the normal sailing lights is impracticable

4

A vessel under oars without sailing lights must show a ready white light in time to prevent collision

5

Motor-sailing under machinery propulsion requires a downward-pointing cone by day

Common Mistakes

Showing optional red-over-green all-round lights together with the combined lantern

Treating merely running an engine for charging as machinery propulsion

Forgetting the daytime cone when sailing while also being propelled by machinery

Test Your Knowledge

Practise this topic and review the explanation for each answer.

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Frequently asked questions about COLREG Rule 25

Which lights does a sailing vessel underway show?

Sidelights and a sternlight (Rule 25(a)). A sailing vessel shows no masthead light, and in a vessel of less than 20 metres the sidelights and sternlight may be combined in one lantern at or near the top of the mast.

What do red over green all-round lights at the masthead mean?

They mark a sailing vessel underway. Rule 25(c) lets her exhibit, in addition to sidelights and sternlight, two all-round lights in a vertical line at or near the top of the mast, the upper red and the lower green. They are optional and must not be used together with the combined mast-top lantern permitted by Rule 25(b).

What light must a vessel under oars show?

She may exhibit the lights prescribed for sailing vessels, or else have ready at hand an electric torch or lighted lantern showing a white light to prevent collision (Rule 25(d)).