Rule 11
Application — in sight of one another
In sight of one another
The give-way rules (12–18) apply only when vessels can actually see each other.
In plain language
Rules 12 through 18 — the whole give-way and stand-on system — apply only to vessels in sight of one another, meaning one can be observed visually from the other. A radar contact in fog is not “in sight”: then Rule 19 governs instead, and there is no stand-on vessel at all.
Takeaway
Give-way and stand-on exist only when you can see each other — on radar in fog, Rule 19 applies instead.