Restricted visibility: collision avoidance and fog signals

Know when Rule 19 applies

Rule 19 applies to vessels not in sight of one another when navigating in or near restricted visibility. Rules 11–18 address vessels in sight. Therefore a contact detected only by radar is not assigned an ordinary crossing stand-on or give-way role merely because its symbol lies on one side of the screen.

Rules 5–8 continue to apply. Keep a lookout by hearing and the other appropriate available means as well as sight. A power-driven vessel must have her engines ready for immediate manoeuvre under Rule 19. A display on an instrument is evidence to interpret, not visual sight of the other vessel.

Safe speed depends on the prevailing conditions

Rule 6 requires a speed that permits effective collision avoidance and stopping within an appropriate distance. Visibility, traffic, manoeuvrability, wind, sea, current, hazards and draught are among the considerations. Operational radar adds further factors, including its limitations and the possibility of missing small targets.

There is no universal fog speed in knots. A number that is appropriate for one vessel and set of conditions may be inappropriate for another. In the safe-speed exercise, inspect the visibility and available warning time, then assess the choice given by the scene. Reducing speed can create time to understand the situation as well as room to stop.

Build an observation rather than a single snapshot

Rules 7 and 19 require assessment of risk and developing close quarters from radar information. Use systematic observations and the available equipment properly; do not make assumptions from scanty radar information. Bearings, range changes and relative motion need to be interpreted together.

When avoiding action for a radar-only contact consists of a course alteration, Rule 19(d) says, so far as possible, to avoid turning to port for a vessel forward of the beam, except one being overtaken. It also says to avoid turning toward a vessel abeam or abaft the beam. These qualifications belong in the explanation; “always turn starboard in fog” is too broad.

Continue checking the result of any action and account for other traffic and navigational dangers. A manoeuvre that opens one contact must not create another close-quarters situation. The authored radar exercise focuses on a selected encounter rather than full radar plotting or every possible multi-target case.

Use a fog signal without inventing its missing details

One prolonged blast generally identifies a power-driven vessel making way. Two prolonged blasts identify a power-driven vessel underway but stopped and making no way through the water. One prolonged followed by two short is shared by several categories, so it does not uniquely establish a sailing vessel, fishing vessel or tow.

A heard signal can alert you to another vessel without establishing her precise range, course or full operation. Listen to the entire pattern and keep seeking appropriate evidence. The stopped-vessel and shared-signal exercises ask you to recognise the limits of what the sound proves.

A signal apparently ahead calls for particular caution

Rule 19(e) addresses hearing another vessel’s fog signal apparently forward of the beam, or being unable to avoid close quarters with a vessel forward of the beam. Except where no collision risk has been determined, reduce to the minimum speed at which the vessel can be kept on course. Take all way off if necessary and navigate with extreme caution until the danger has passed.

In revision, explain the condition that triggers this duty before stating the action. In passage preparation, bring together lookout, engine readiness, signalling equipment, safe speed and the route’s hazards. Weather decisions and passage planning extend beyond these exercises; use the current forecast and local publications for the voyage itself.