Rule 19 — Restricted Visibility

Rules 4–10 apply in any visibility; Rules 11–18 only when vessels are in sight; Rule 19 applies to vessels not in sight in or near restricted visibility. It is safer than saying Rule 19 simply 'replaces Rules 12–18': localised fog can leave one contact visually in sight and another unseen, so classify each encounter.

Every vessel proceeds at a safe speed adapted to the circumstances, and a power-driven vessel has engines ready for immediate manoeuvre. Use operational radar properly, including long-range scanning and systematic plotting. When altering course on radar information alone, avoid port for a vessel forward of the beam except when overtaking, and avoid altering towards a vessel abeam or abaft the beam. These cautions are not an automatic command to turn starboard.

If a fog signal is heard apparently forward of the beam, or close quarters cannot be avoided with a vessel forward of the beam, reduce to the minimum speed at which the vessel can be kept on course. If necessary take all way off and navigate with extreme caution until danger is over. There is no universal CPA or TCPA minimum.

At intervals of not more than two minutes, Rule 35 uses one prolonged blast for a power-driven vessel making way; two prolonged for one underway but stopped; and one prolonged plus two short for the listed sailing, fishing, NUC, RAM, constrained-by-draught, towing and pushing categories. Sound identifies status or movement; it does not allocate stand-on and give-way roles.