Official rule text as published in the U.S. Coast Guard Navigation Rules
(a) Rules 20-31 shall be complied with in all weathers.
(b) The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights which cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out.
(c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.
(d) The Rules concerning shapes shall be complied with by day.
(e) The lights and shapes specified in these Rules shall comply with the provisions of Annex I of these Rules.
| Inland |
|---|
| (f) A vessel's navigation lights and shapes may be lowered if necessary to pass under a bridge. |
MyCOLREGS explanation
Summary
Rules 20-31 (lights and shapes) apply in all weather, not just at night or in fog. The light rules themselves run from sunset to sunrise, and during that window you cannot show any other light that could be confused with a required light, wash out its visibility, or interfere with someone else's lookout - though required lights may also be shown in daytime restricted visibility or whenever it seems necessary. Shapes are a daytime signal. All of it has to match the technical specifications in Annex I. On U.S. inland waters there is one practical exception: lights and shapes may be lowered if that is necessary to clear a bridge.
Real World Example
A cockpit strung with party lights or a spotlight left burning isn't just tacky - if it can be confused with a required light or wash out its visibility, Rule 20(b) makes it a violation, because another skipper's read of your type and heading depends on picking the right lights out of the clutter. Get that wrong, and someone miles off may commit to a turn based on a boat that, correctly lit, would have looked entirely different.
Practice Questions
Q1. A recreational boater asks why navigation lights matter if the boat is already showing up fine on the other vessel's AIS. What is the best answer under Rule 20's framework?
A. Lights and shapes communicate vessel type, aspect, and activity to any observer, AIS or not, and Rules 20-31 apply in all weather regardless of what electronics a vessel carries.
B. Lights do not matter if AIS is transmitting, since any vessel checking AIS already has everything needed to identify type, position, and heading.
C. Only commercial vessels are required to comply with the lighting rules, since recreational boaters are assumed to rely on electronics instead.
D. Lights are purely decorative and optional on recreational vessels, since Rules 20-31 were written before AIS existed and are now largely obsolete.
Q2. You've strung festive white party lights across the deck for a night cruise, in addition to your required navigation lights. Under Rule 20(b), is that allowed?
A. Only on inland waters; the International Rules prohibit any additional lighting after sunset regardless of how dim or well-shielded it is.
B. Yes, any lights are permitted after sunset as long as the vessel's engine remains running, since Rule 20(b) is only concerned with vessels at anchor or adrift.
C. No - Rule 20(b) allows only lights that cannot be mistaken for the prescribed lights, don't impair their visibility, and don't interfere with keeping a proper lookout; string lights near your sidelights risk exactly that.
D. No - Rule 20(b) bans all non-required lighting outright, with no exceptions of any kind, including interior cabin lighting visible through a porthole.
Practice Question Answers
Q1.
A. Lights and shapes communicate vessel type, aspect, and activity to any observer, AIS or not, and Rules 20-31 apply in all weather regardless of what electronics a vessel carries. Rule 20(a) requires Rules 20-31 to be complied with in all weathers, and the whole point of the light/shape system is to let any other vessel - with or without AIS - read your type and aspect visually. B assumes AIS can substitute for lights, which Rule 20 doesn't allow. C invents a commercial-only limitation the rule doesn't contain. D dismisses lighting as decorative, when it's a core communication requirement independent of any electronics carried.
Q2.
C. Sunset to sunrise; no other lights may be shown except ones that cannot be mistaken for, or impair, the prescribed lights, or interfere with a proper lookout. Rule 20(b) sets the sunset-to-sunrise window for lights and restricts any other lighting that could be confused with, or degrade the visibility of, the required navigation lights or interfere with keeping a proper lookout. A invents a storm-specific condition not in the rule. C gets both the hours wrong and inverts the restriction on other lights. D also gets the hours backwards and overstates the requirement - the rule doesn't require extinguishing all other lights, just avoiding ones that could be confused with or impair the prescribed lights.