Official rule text as published in the U.S. Coast Guard Navigation Rules
Rules in this Section apply in any condition of visibility.
MyCOLREGS explanation
Summary
Rule 4 may be the shortest rule in the book, but don’t overlook it. Its single sentence sets the stage for everything through Rule 19. In all conditions of visibility—whether you’re cruising on a clear, sunny afternoon, running at night, or navigating through rain or thick fog—the rules for lookout, safe speed, risk of collision, and collision avoidance all apply. These rules don’t switch on when visibility gets bad; they are always in effect.
Real World Example
It's tempting to relax lookout and speed discipline the moment conditions look easy, or to assume a looser standard applies once fog rolls in. Rule 4 closes that gap: the entire section that follows carries the same weight in every condition of visibility, so there's no threshold at which the duties in Rules 5 through 19 quietly ease up.
Practice Questions
Q1. You're running in bright, calm, ten-mile visibility with nothing else on the water. Do the lookout, safe-speed, and risk-of-collision rules still apply exactly as they would in fog?
A. No - those rules are meant for restricted visibility only.
B. Yes - Rule 4 makes the entire following section apply in any condition of visibility, including perfect visibility.
C. Only the lookout rule applies in good visibility; safe speed and risk of collision are for fog.
D. It depends on vessel size.
Q2. Heavy rain has cut visibility to about 2 miles - not thick fog, but well short of a clear day. A boater argues Rule 4's "any condition of visibility" language was really only written with fog in mind, so the ordinary conduct rules haven't fully kicked in yet at 2 miles. Is he right?
A. Yes - Rule 4 only takes effect once visibility drops into what would reasonably be called fog, since the rule was written specifically to address the classic thick-weather collision scenario.
B. No - Rule 4 applies the following Section in any condition of visibility, with no threshold or exception for moderate reductions like rain.
C. No, but only because 2 miles happens to fall under a specific numeric cutoff written into Rule 4, below which the full conduct requirements are triggered automatically.
D. It depends on whether the vessel is using radar, since Rule 4 only applies to radar-equipped vessels once visibility falls below what an unaided lookout could reasonably see.
Practice Question Answers
Q1.
B. Yes - Rule 4 makes the entire following section apply in any condition of visibility, including perfect visibility. Rule 4's one sentence is easy to skim past, but it's doing real work: it removes any argument that good visibility lowers the bar. Rules 5 through 19 apply the same whether you can see for ten miles or ten feet. A and C both assume good visibility lowers the bar, treating some of these duties as fog-only requirements. D substitutes vessel size for the actual, universal condition Rule 4 sets: these rules apply in any visibility, full stop.
Q2.
B. The rules in this Section apply in any condition of visibility. That's the entire rule, verbatim. It's short because its job is simple: state plainly that nothing in Rules 5 through 19 gets weaker just because you can see well. A invents a size-based exemption Rule 4 doesn't grant. C invents a radar-based exception to the lookout duty. D wrongly assumes visibility determines which rules apply by vessel type, when Rule 4's actual text is a blanket statement with no such carve-outs.