COLREGs · Rule 20 · 33 CFR §83.20
Application (Lights and Shapes)
Lights are exhibited from sunset to sunrise and in restricted visibility. Shapes are exhibited by day. Annex I governs the technical particulars.
What does Rule 20 actually say?#
Source
Practice this rule#
One real exam question on this rule, cited to source. No sign-up.
Under the International Rules, a vessel constrained by her draft underway in restricted visibility shall sound ______.
How does Inland Rule 20 differ from COLREGs?#
Inland Rule 20 adds a paragraph (f) that COLREGs does not have: a vessel's navigation lights and shapes may be lowered if necessary to pass under a bridge. It is a small provision with an obvious inland reason, and it is exactly the kind of detail an Inland-specific question is built from.
21 of 38 rules differ somewhere; the five the exam leans on are Rule 9, Rule 10, Rule 24, Rule 28 and Rule 34, side by side on Inland vs International Rules.
Why it shows up on the exam#
Rule 20 is the scoping rule for the whole lights-and-shapes section, and almost all of its exam value is in the timing: lights from sunset to sunrise, lights also by day in restricted visibility, shapes by day.
What does the exam actually test here?#
Lights
Sunset to sunrise
The rules concerning lights shall be complied with from sunset to sunrise, and during those hours no other lights may be exhibited except ones that cannot be mistaken for the prescribed lights, do not impair their visibility or distinctive character, and do not interfere with keeping a proper look-out.
Lights by day
In restricted visibility
The prescribed lights, if carried, shall also be exhibited from sunrise to sunset in restricted visibility, and may be exhibited in all other circumstances when it is deemed necessary.
Shapes
By day
The rules concerning shapes shall be complied with by day. Lights and shapes must meet Annex I (33 CFR part 84), and the section as a whole must be complied with in all weathers.
Rule 20 — common exam questions#
When must navigation lights be exhibited?
From sunset to sunrise, and also from sunrise to sunset in restricted visibility — and they may be exhibited at any other time when deemed necessary (33 CFR §83.20(b) and (c)).
Can a vessel show other lights at night?
Only lights that cannot be mistaken for the lights specified in the Rules, do not impair their visibility or distinctive character, and do not interfere with keeping a proper look-out (33 CFR §83.20(b)).
Do you need navigation lights in fog during the day?
Yes. Rule 20(c) requires the prescribed lights, if carried, to be exhibited from sunrise to sunset in restricted visibility.
Can navigation lights be lowered to pass under a bridge?
Under the Inland Rules, yes — Rule 20(f) allows a vessel's navigation lights and shapes to be lowered if necessary to pass under a bridge (33 CFR §83.20(f)). COLREGs has no equivalent paragraph.
Authoritative source#
- 33 CFR §83.20 — this section with its neighbours. 33 CFR Part 83 is public domain; checked 2026-05-16.
- COLREGs Rule 20 is published by the IMO and is authoritative internationally.
Practise this rule against the real exam.
Real exam questions. No signup, no card.
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