Reduced visibility is any condition — fog, heavy rain, snow, sandstorm, or similar — that limits sight distance below normal levels, triggering specific navigational obligations under COLREGS Rule 19.
What Rule 19 Requires
- Safe speed — specifically adapted to the prevailing reduced-visibility conditions, genuinely slower than normal operating speed given the reduced ability to see and react to hazards
- Fog signals — sound signals specified under COLREGS Rule 35, alerting other vessels to your presence when they can’t see you visually
- Full use of radar — since visual lookout alone is inadequate in these conditions, radar becomes the primary means of detecting other vessels and hazards
- Readiness to take avoiding action — including reducing speed further or stopping engines if a close-quarters situation develops
Why Reduced Visibility Rules Differ From Normal COLREGS
Rule 19’s requirements exist specifically because the normal visual give-way/stand-on framework depends on being able to see other vessels — in fog or similarly limiting conditions, that visual information isn’t available, so the rules shift toward caution, radar reliance, and audible signaling instead.
Practical Bridge Response
Entering reduced visibility conditions typically triggers a real, practiced bridge response: reducing speed, posting an additional lookout, activating fog signals, increasing radar/ARPA monitoring, and often calling the Master to the bridge if not already present — a genuine operational shift, not just a mental note.
Exam Relevance
COLREGS Rule 19 requirements for reduced visibility — safe speed, fog signals, and radar use — are core, heavily-tested Navigation and COLREGS topics in deck officer competency exams.