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23

Power-driven Vessels Underway

Power-driven vessels underway shall exhibit masthead light(s), sidelights, and sternlight. Vessels 50m+ require two masthead lights.

Rule 23 specifies lights for power-driven vessels underway.

a
A power-driven vessel underway shall exhibit:
  • 1A masthead light forward
  • 2A second masthead light abaft of and higher than the forward one — except that a vessel of less than 50 metres in length shall not be obliged to exhibit such light but may do so
  • 3Sidelights — red (port) and green (starboard)
  • 4A sternlight
b
An air-cushion vessel when operating in the non-displacement mode shall, in addition, exhibit an all-round flashing yellow light.

Recognition Sequence

1

Classify the vessel state first: underway, making way, stopped, at anchor, aground, towing, fishing, pilotage or special condition.

2

Read special lights vertically from top to bottom before using sidelights and sternlight to confirm aspect.

3

Then confirm the answer with the day shape, vessel length and any extra signal such as towing lights, deck illumination or a cylinder.

Exam Focus

1

Avoid identifying a vessel from one colour alone. Many mistakes come from spotting a red light and guessing before checking the full pattern.

2

If the question mentions 'making way', 'underway but stopped', 'at anchor' or 'aground', that wording usually determines which extra lights or shapes appear.

Key Takeaways

1

Vessels 50m+ must show two masthead lights

2

All power-driven vessels show sidelights and sternlight

3

Second masthead light must be higher than the forward one

4

Hovercraft show additional flashing yellow light

Common Mistakes

Small vessels displaying two masthead lights unnecessarily

Confusing the vertical positioning of forward and after masthead lights

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