Rules 11 to 18 apply only to vessels in sight of one another.
Rule 11: Application
Rules in this Section apply to vessels in sight of one another.
In plain words: Section II is Rules 11 to 18 (sailing vessels, overtaking, head-on, crossing, give-way and stand-on action, and responsibilities between vessels). Vessels are in sight of one another only when one can be observed visually from the other (Rule 3(k)). When vessels are not in sight of one another in or near restricted visibility, Section II does not apply: Rule 19 does, together with Section I. A radar contact in fog is not a vessel in sight.
Wording follows the International Regulations as printed in the US Coast Guard Navigation Rules handbook (2024), with British spelling, and is shortened in places. Download the rules
Read the whole of Rule 11 on one page
Rule 11: Application
Rules in this Section apply to vessels in sight of one another.
In plain words: Section II is Rules 11 to 18 (sailing vessels, overtaking, head-on, crossing, give-way and stand-on action, and responsibilities between vessels). Vessels are in sight of one another only when one can be observed visually from the other (Rule 3(k)). When vessels are not in sight of one another in or near restricted visibility, Section II does not apply: Rule 19 does, together with Section I. A radar contact in fog is not a vessel in sight.
A training aid, not the official text. The COLREGs are an IMO convention, and your national authority publishes the version that applies in its waters. Check the rules themselves before you rely on them at sea. Download the rules.