IALACOLREG
22

Visibility of Lights

Minimum visibility ranges by vessel length (table).

Rule 22 establishes the minimum ranges of visibility for navigation lights based on vessel length. The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I so as to be visible at the following minimum ranges:

In vessels of 50 metres or more in length:

  • Masthead light — 6 nm
  • Sidelight — 3 nm
  • Sternlight — 3 nm
  • Towing light — 3 nm
  • White, red, green or yellow all-round light — 3 nm

In vessels of 12 metres or more but less than 50 metres in length:

  • Masthead light — 5 nm (except that where the length of the vessel is less than 20 metres — 3 nm)
  • Sidelight — 2 nm
  • Sternlight — 2 nm
  • Towing light — 2 nm
  • White, red, green or yellow all-round light — 2 nm

In vessels of less than 12 metres in length:

  • Masthead light — 2 nm
  • Sidelight — 1 nm
  • Sternlight — 2 nm
  • Towing light — 2 nm
  • White, red, green or yellow all-round light — 2 nm

In inconspicuous, partly submerged vessels or objects being towed: - White all-round light — 3 nm

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.

Then confirm the answer with the day shape, vessel length and any extra signal such as towing lights, deck illumination or a cylinder.

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

≥50m vessels: masthead 6 nm, all other lights 3 nm

2

12–<50m vessels: masthead 5 nm (3 nm if <20m), sidelights/sternlight/all-round 2 nm

3

<12m vessels: masthead 2 nm, sidelights 1 nm, sternlight/all-round 2 nm

4

Inconspicuous towed objects: white all-round 3 nm

Common Mistakes

Using under-powered lights that don't meet minimum range requirements

Forgetting the masthead-light step-down to 3 nm for 12–20m vessels

Forgetting that on <12m vessels the sidelight range (1 nm) drops below the sternlight range (2 nm)

Test Your Knowledge

Test your knowledge and prove your mastery.

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