1The rule in plain words
In one sentence…
Rule 22 in COLREG sets the minimum visible range for each light according to vessel length or the category of the object being towed.
Vessels of 50 m or more?
The masthead light: 6 miles. Sidelight, sternlight, towing light and white, red, green or yellow all-round light: 3 miles. These are minimum ranges.
Vessels 12 m or more but less than 50 m?
The masthead light has a minimum range of 5 miles; when length is less than 20 m, 3 miles. The other prescribed lights have 2 miles; the masthead light is the exception.
Vessels less than 12 m?
Masthead light, 2 miles; sidelight, 1 mile; sternlight, towing light and all-round light, 2 miles. Remember that the sidelight has 1 mile.
Inconspicuous, partly submerged vessels or objects being towed?
Their white all-round light must be visible at a minimum range of 3 miles (the light itself is prescribed by Rule 24(g)).
2Key points
- 1.
Classify by vessel length first; then identify the light.
- 2.
Greater length → generally greater minimum ranges.
- 3.
The masthead light carries the exception in the middle band.
- 4.
An inconspicuous towed object has its own category.
3Frequent mistakes
Wrong: "All lights have to be visible at the same distance."
Right: The minimum range depends on vessel length and light type.
Wrong: "Rule 22 specifies colours, but not distance."
Right: It sets minimum visibility ranges; intensity is referred to Annex I.
Wrong: "A partly submerged towed object uses the vessel-length table."
Right: Paragraph (d) gives that object category its own prescription.
4Exam keys & interpretation
Exam keys
Read "50 metres or more": a vessel exactly 50 metres belongs in the first band.
In the middle band, "less than 20 metres" changes the masthead light from 5 to 3 miles.
For an inconspicuous, partly submerged towed object, check paragraph (d), not a vessel-length band.
How to read it
Classify by the exact description: vessel length or the condition of the towed object; do not mix categories.
Then compare light type and minimum range; "minimum" marks the required threshold.
5Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I to these Regulations so as to be visible at the following minimum ranges:
(a) In vessels of 50 meters or more in length:
− a masthead light, 6 miles;
− a sidelight, 3 miles;
− a sternlight, 3 miles;
− a towing light, 3 miles;
− a white, red, green or yellow all-round light, 3 miles.
(b) In vessels of 12 meters or more in length but less than 50 meters in length:
− a masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles;
− a sidelight, 2 miles;
− a sternlight, 2 miles;
− a towing light, 2 miles;
− a white, red, green or yellow all-round light, 2 miles.
(c) In vessels of less than 12 meters in length:
− a masthead light, 2 miles;
− a sidelight, 1 mile;
− a sternlight, 2 miles;
− a towing light, 2 miles;
− a white, red, green or yellow all-round light, 2 miles.
(d) In inconspicuous, partly submerged vessels or objects being towed:
− a white all-round light, 3 miles.6Test your knowledge
In a vessel of 50 m or more, what is the minimum range of the masthead light?
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