Part CBasic
Rule 20: Application of lights and shapes
Sets when lights and shapes must be shown and forbids confusing extra lights.
Detailed Explanation
Navigation lights and shapes must be displayed at prescribed times and must never be confused with authorised signals.
A
Part C applies in all weathers.
B
Light rules apply from sunset to sunrise. During this time, no other lights unless they cannot be mistaken for COLREG lights, do not impair visibility/distinctive character, and do not interfere with look-out.
C
Prescribed lights are also shown by day in restricted visibility and may be shown in other circumstances if needed.
D
Shape rules apply by day.
E
All specified lights/shapes must comply with Annex I.
Key Points
- Lights: sunset to sunrise and reduced visibility
- No other lights that could mislead or impair detection
- Shapes displayed by day for same statuses
Examples
- At sunset you switch on navigation lights for your cargo ship even though visibility is still good. Rule 20(a) requires lights from sunset to sunrise regardless of conditions.
- A fishing vessel adds a powerful deck light for working at night. Rule 20(b) says additional lights must not be mistaken for required navigation lights or impair their visibility.
Common Mistakes
- Switching off navigation lights at dawn while still in restricted visibility.
- Installing decorative or commercial lighting that can be confused with required navigation lights.
- Displaying shapes at night or lights by day when the rule does not require them, causing confusion.