Rule 19 — Conduct in Restricted Visibility

Rules 11–18 form the section for vessels in sight of one another. When the other vessel is not visually in sight in or near restricted visibility, Rule 19 applies and there is no Section II stand-on vessel. Rules 4–10 still apply, including proper lookout, safe speed, risk assessment and effective avoiding action. Obligations not to impede another vessel under Rules 9, 10 and 8(f) can also continue in restricted visibility.

When another vessel is detected by radar alone, determine whether a close-quarters situation or risk of collision is developing from systematic observations. If so, take avoiding action in ample time. When that action is an alteration of course, Rule 19 says that so far as possible avoid an alteration to port for a vessel forward of the beam, except when overtaking, and avoid an alteration towards a vessel abeam or abaft the beam. Those cautions do not make every starboard turn safe: check the full plot, sea room, other targets and the effect of the action.

Except where risk has been determined not to exist, if a fog signal is heard apparently forward of the beam, or a close-quarters situation cannot be avoided with another 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 in every case navigate with extreme caution until the danger of collision is over. Sound direction can be deceptive, and small craft may not be detected by radar, so absence of a plotted target is not proof that the danger is absent.