Safe Speed in Fog (Rule 6)
Visibility is under 1 NM and AIS shows dense traffic. Rule 6 requires every vessel to proceed at a SAFE SPEED appropriate to prevailing conditions.
Scenario briefing
Visibility is under 1 NM and AIS shows dense traffic. Rule 6 requires every vessel to proceed at a SAFE SPEED appropriate to prevailing conditions. Rule 19(b) reinforces this for restricted visibility. Reduce SOG to 6 kt, then click EVALUATE.
Applicable COLREG rule(s)
📸 Bridge simulator scene
Captured directly from the SkipperCheck COLREG bridge simulator at scenario T = 0 — the moment the encounter begins.
Key teaching points
- Rule 6 is always in force, not just in fog. Heavy traffic, manoeuvrability, draught and background lights all weigh in.
- In restricted visibility, Rule 19(b) reinforces that safe speed must be adapted to the prevailing circumstances.
- For a power-driven vessel in fog with dense traffic, that typically means well under hull speed and ready to take all way off.
- Radar-equipped vessels must consider the characteristics, efficiency and limitations of their radar (Rule 6(b)).
Common mistakes to avoid
- Maintaining cruise speed in fog because "we have radar and AIS". Both can miss small craft, ice, debris and unlit objects.
- Reducing speed only AFTER a target appears — Rule 6 demands pre-emptive setting of safe speed before the encounter develops.
Why it matters
Exam relevance
Safe speed is a near-universal oral exam question for RYA Yachtmaster Coastal/Offshore, STCW OOW and ICC — examiners probe whether the candidate names the Rule 6 factors and applies them to the actual conditions described.
Related scenarios
About SkipperCheck simulators
SkipperCheck offers two browser-based maritime training simulators:
- ARPA · AIS · COLREG Bridge Simulator — 54 scenarios covering Rules 2, 5–10, 12–19, 23–30, 34 and 35.
- VHF SRC Radio Simulator — 15 scenarios: voice Mayday, DSC distress, Mayday Relay, Pan-Pan, Sécurité, routine.
Both run in any modern browser, on desktop or mobile. No install, no plugins.