COLREG - Fog Signal Pattern Lookup
Required sound signal pattern in restricted visibility per COLREG Rule 35 by vessel type and operational status.
Formula, assumptions, limits
COLREG Rule 35 prescribes fog signals by vessel type and status. Signals are sounded at intervals not exceeding 2 minutes (or 1 minute for vessels at anchor or aground). The whistle (or fog horn) is the primary signal device; bells and gongs supplement for anchored and aground vessels.
Sound signal patterns
Vessel/StatusPatternInterval
Power-driven, making wayOne prolonged blastat most 2 min Power-driven, stoppedTwo prolonged blastsat most 2 min Sailing, fishing, towing, RAM, NUCOne prolonged + two shortat most 2 min Vessel being towed (last vessel of tow)One prolonged + three shortat most 2 min Anchored vessel Bell rapidly 5 secat most 1 min Anchored vessel >=100 mBell forward + gong aftat most 1 min Aground vesselThree bell strokes + bell rapidly + three bell strokesat most 1 min Pilot vessel on dutyAbove signals + four short blastsat most 2 min
Prolonged blast = 4 to 6 seconds. Short blast = approximately 1 second.
In short
Required fog signal pattern per COLREG Rule 35.