Rule 4

Application — any visibility

Any visibility

Rules 4–10 apply in every condition of visibility — clear day, black night, or thick fog.

In plain language

Part B of the rules comes in three sections. This first section — look-out, safe speed, risk of collision, avoiding action, narrow channels, and traffic schemes — applies all the time, whether or not you can see the other vessel. The in-sight rules (11–18) and the restricted-visibility rule (19) then layer on top.

Takeaway

Look-out, safe speed, and collision-risk rules never switch off.