Rule 19 — Restricted Visibility

Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility (fog, heavy rain, snow, etc.). It replaces Rules 12–18 when vessels cannot see each other visually.

Every vessel must proceed at a safe speed adapted to the prevailing visibility. If fitted with radar, use it — including long-range scanning for early warning and radar plotting or equivalent systematic observation of detected objects. A vessel that hears a fog signal apparently forward of her beam, or cannot avoid a close-quarters situation with a vessel forward of her beam, must reduce speed to the minimum at which she can be kept on course, and if necessary take all way off.

When taking avoiding action based on radar information alone: avoid altering course to port for a vessel forward of the beam (except when overtaking), and avoid altering course toward a vessel abeam or abaft the beam. Sound signals in restricted visibility include one prolonged blast at intervals of not more than two minutes (power-driven vessel making way), two prolonged blasts at not more than two minutes (power-driven vessel underway but stopped), and one prolonged followed by two short blasts (sailing, fishing, NUC, RAM, CBD, towing).