1The rule in plain words
In one sentence…
Every vessel keeps a proper look-out at all times, by sight, hearing and appropriate available means, to fully appraise the situation and risk of collision.
Who and when?
Your vessel shall maintain a proper look-out at all times. The duty applies to every vessel.
How?
Look and listen: the look-out must be by sight and hearing. Both are part of a proper look-out.
What else do you use?
Also use all available means appropriate in the prevailing circumstances and conditions, such as radar or AIS.
What is it for?
With this look-out, you make a full appraisal of the situation and of the risk of collision.
2Key points
- 1.
Universal duty · continuous look-out.
- 2.
Sight + hearing → proper look-out.
- 3.
Available means = appropriate to the moment.
- 4.
Purpose → full situation appraisal + collision risk.
3Frequent mistakes
Wrong: "A look-out matters only when traffic is busy."
Right: Rule 5 requires you to maintain it at all times.
Wrong: "A small leisure craft is outside Rule 5."
Right: The rule says every vessel; it creates no such exemption.
Wrong: "Radar or AIS replace looking and listening."
Right: Radar and AIS add means; they do not replace look-out by sight and hearing.
4Exam keys & interpretation
Exam keys
If an option exempts an anchored vessel or small leisure craft, reject it: the rule says "every vessel".
"Radar/AIS" does not replace "sight and hearing": check whether the option adds means or removes the look-out.
If asked for the purpose, look for a full appraisal of situation and collision risk, not merely detecting another vessel.
How to read it
"Appropriate" depends on the prevailing circumstances and conditions: use available means that help you make a full appraisal of the situation.
"As well as" adds means to sight and hearing; it does not turn equipment into a substitute for the look-out.
5Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.6Test your knowledge
Who must comply with Rule 5, and when?
Apply Rule 5: two lookout decisions
COLREG · USCG NAVCEN · 2026-09-10Near a harbour at night, a small boat's light is visible against bright shore lights, but the radar shows no clear echo. The watchkeeper has been looking only at the display.
Can the radar picture justify dismissing the boat?
No. Restore an attentive visual and hearing watch, report the observed light, and use the available radar appropriately alongside those observations. Keep observing the boat systematically to assess its movement and collision risk.
Rule 5 combines sight, hearing and appropriate available means. Small targets may escape radar detection, and shore lights can mask navigation lights. A missing echo is not evidence that a visible boat or collision risk has disappeared.
Your vessel is anchored in clear daylight near passing traffic. The crew proposes leaving the lookout unattended because the engine is stopped and visibility is good.
Does being at anchor remove the lookout duty?
No. Maintain an effective lookout by sight and hearing, using other appropriate available means. Arrange relief before other duties interrupt that watch, and continue assessing approaching traffic and changes around the vessel.
Rule 5 applies to every vessel at all times. Anchoring and good weather do not remove the need to detect and appraise hazards; the means used must suit the actual conditions.
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