Navigating in Fog

There is no single visibility distance that is safe for every yacht and route. The usable distance depends on traffic, closing speeds, sea room, navigation hazards, the yacht's stopping and turning ability, the available crew and the equipment that can genuinely be used. If there is no target against which to judge visibility and the skipper believes it is restricted, MCA guidance says to assume that it is and act accordingly.

The strongest decision is often made before entering the affected area. Check the forecast and actual observations, the route's traffic and hazards, escape or anchoring options, daylight, crew capacity and whether radar or other aids are fitted and understood. Delay, shorten or divert when the remaining margin does not support safe lookout, navigation and collision avoidance; a planned departure is not a commitment to enter conditions the crew cannot manage.

Restricted visibility should already appear in the passage plan as a trigger, not be invented after the horizon disappears. Name the decision point, a safe alternative and the evidence that will be monitored. A position, depth, radar return or AIS target is one item of evidence, never permission to keep the original speed or route when the wider situation is becoming unsafe.