COLREG - Fog Signal Pattern Lookup
Required sound signal pattern in restricted visibility per COLREG Rule 35 by vessel type and operational status.
Sound signal pattern
One prolonged blast
Frequency
At intervals of not more than 2 minutes
Formula, assumptions, and 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/Status | Pattern | Interval |
|---|---|---|
| Power-driven, making way | One prolonged blast | at most 2 min |
| Power-driven, stopped | Two prolonged blasts | at most 2 min |
| Sailing, fishing, towing, RAM, NUC | One prolonged + two short | at most 2 min |
| Vessel being towed (last vessel of tow) | One prolonged + three short | at most 2 min |
| Anchored vessel <100 m | Bell rapidly 5 sec | at most 1 min |
| Anchored vessel >=100 m | Bell forward + gong aft | at most 1 min |
| Aground vessel | Three bell strokes + bell rapidly + three bell strokes | at most 1 min |
| Pilot vessel on duty | Above signals + four short blasts | at most 2 min |
Prolonged blast = 4 to 6 seconds. Short blast = approximately 1 second.
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