1The rule in plain words
In one sentence…
COLREG: white over red, pilot ahead; underway or at anchor add lights or shapes; off duty uses those for a similar vessel of her length.
Which lights identify pilotage duty?
At or near the masthead, she shows two all-round lights in a vertical line; the upper is white and the lower is red.
What is added when underway?
Besides the masthead pair, she shows sidelights and a sternlight.
What changes when she is at anchor?
In addition to the lights in (i), she shows the anchor light, lights, or shape prescribed in Rule 30.
What if she is not on pilotage duty?
She shows the lights or shapes prescribed for a similar vessel of her length.
2See it in 3D
Turn the vessel or pick bow, stern, port or starboard: this is how her lights look at night.
An interactive 3D illustration is shown here. The same content is described in the rule text and key takeaways below.
3Key points
- 1.
Pilotage duty → white above red · vertical pair.
- 2.
Underway → add sidelights + sternlight.
- 3.
At anchor → add Rule 30: light, lights, or shape.
- 4.
Off duty → lights or shapes for a similar vessel of her length.
4Frequent mistakes
Wrong: "White over red means she is at anchor."
Right: It marks pilotage duty; at anchor she also shows the Rule 30 light, lights, or shape.
Wrong: "When underway she shows only the masthead pair."
Right: When underway, she adds sidelights and a sternlight.
Wrong: "Off duty she always keeps the pilotage lights."
Right: Off duty, she shows the lights or shapes for a similar vessel of her length.
5Exam keys & interpretation
Exam keys
"Engaged on pilotage duty" activates white over red; "not engaged" points to a similar vessel.
"When underway" means sidelights and a sternlight in addition to the vertical pair.
"At anchor" does not remove the vertical pair: add the Rule 30 light, lights, or shape.
How to read it
Classify the status first: pilotage duty, underway, or at anchor; then add the required lights or shapes.
When not engaged on pilotage duty, apply the lights or shapes prescribed for a similar vessel of her length.
6Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
(a) A vessel engaged on pilotage duty shall exhibit:
(i) at or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red;
(ii) when underway, in addition, sidelights and a sternlight;
(iii) when at anchor, in addition to the lights prescribed in subparagraph (i), the anchor light, lights, or shape prescribed in Rule 30 for vessels at anchor.
(b) A pilot vessel when not engaged on pilotage duty shall exhibit the lights or shapes prescribed for a similar vessel of her length.7Test your knowledge
A vessel engaged on pilotage duty: what does she show at the masthead?
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