COLREG Rule 5 — Lookout
Every vessel shall at all times maintain a proper lookout by sight and hearing as well as by all available means appropriate.
In practice
Bridge watch arrangements ensure proper lookout at all times — visually and by radar. Lone-OOW operation in restricted visibility is the classical Rule 5 failure.
Regulatory detail & full definition
COLREG Rule 5 — Look-out: 'Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.' The duty is unconditional and overrides every other rule. Radar, AIS, ECDIS, and electronic aids supplement but never replace the visual and aural watch. Many reported collisions trace to a Rule 5 failure — typically a single OOW distracted by paperwork while autopilot held course in restricted visibility.
Authoritative source: COLREG 1972 ↗
Related
Source: COLREG 1972 Rule 5
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