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4

Application

Rules 4–10 apply in any visibility. A vessel can still be in sight in mist; a radar contact alone is not visual observation. The visible vessel in restricted visibility also displays its prescribed navigation lights.

Rule 4 clarifies that the rules in Section I (Rules 4–10) apply in any condition of visibility, whether clear or restricted. This is distinct from Section II rules which only apply when vessels are in sight of one another, and Section III which applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.

IMO COLREG 1972Official text

Full wording of the rule, reproduced from the official source below.

Rules in this Section apply to any condition of visibility.
Source:

STCW Bridge Watch Lens

Rules 4–10 apply in any visibility.

Rules 11–18 apply to vessels in sight of one another; Rule 19 applies to vessels not in sight when navigating in or near an area of restricted visibility.

Build the traffic picture with sight, hearing, radar/ARPA and chart context.

Do not let AIS or one isolated bearing replace systematic observation.

After manoeuvring, keep monitoring bearing, range, CPA/TCPA and passing distance until the other vessel is finally past and clear.

Exam Focus

Start every scenario by classifying the encounter: overtaking, head-on, crossing, narrow channel, traffic separation, or restricted visibility.

For vessels in sight, every overtaking vessel keeps clear until finally past and clear.

Rule 13 takes precedence over Part B Sections I and II; it does not override the other Parts of COLREG.

Key Takeaways

1

Section I rules apply in ALL visibility conditions

2

These are the fundamental steering and sailing rules

3

Must be followed regardless of weather or visibility

Common Mistakes

Thinking different steering rules apply in fog vs clear weather for Section I

Test Your Knowledge

Practise this topic and review the explanation for each answer.

More rules in this Part

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Frequently asked questions about COLREG Rule 4

Which COLREG rules apply in any condition of visibility?

Rules 4 to 10, the Section I steering and sailing rules. Rule 4 states that they apply in any condition of visibility, whether clear or restricted.

Do different steering rules apply in fog under Section I?

No. The Section I rules must be followed regardless of weather or visibility. Thinking that different steering rules apply in fog and in clear weather is a common mistake.

How do Sections I, II and III of Part B differ?

Section I (Rules 4–10) applies in all visibility conditions. Section II applies only when vessels are in sight of one another, and Section III applies to vessels not in sight of one another when navigating in or near restricted visibility.