In fog, the main hazard is not only losing the shoreline. Other vessels, fixed hazards and the approach to a harbour become harder to assess. A good chartplotter does not show every small craft or floating object, and AIS does not include every vessel.
Decide before departure
Read the latest official forecast and visibility observations for the route and destination, including the expected trend and time of arrival. Consider traffic density, narrow channels, fishing activity, currents, daylight and the crew’s competence with the boat’s equipment. If visibility is likely to be inadequate for the route, delay rather than treating radar or AIS as permission to proceed.
If visibility falls while underway
Follow the applicable collision-prevention rules, including the rules for restricted visibility and required sound signals. Proceed at a safe speed for the conditions and be prepared to take all way off if necessary. Keep an effective visual and hearing lookout; use radar properly if fitted, while remembering its limits. Cross-check position with independent information. Assign roles so that the person navigating is not the only lookout.
Reassess the destination
A narrow, unfamiliar or busy entrance may be more hazardous than remaining in safe open water or diverting. Compare the latest local information with the boat’s position and fuel or power reserves. Do not invent a universal visibility threshold: the decision depends on the vessel, equipment, traffic and waterway. Inform the crew of the revised plan and call for help when needed.
Before the next trip
Practise radar interpretation, position cross-checks, lookout and sound-signal procedures in clear conditions. Technology supports, but cannot replace, watchkeeping and the COLREGs.
Official sources
- NOAA/NWS: Fog safety for boaters
- IMO: Convention on the International Regulations for Preventing Collisions at Sea
- UK MCA: Navigation in restricted visibility
Important: This is practical passage guidance, not a forecast for your specific departure or a navigational route. Personalised forecasts with AI and experts are in closed testing. Before and during a passage, check the latest official forecasts and warnings for your area; the skipper decides in light of actual conditions, vessel and crew.
Separate weather evidence from equipment confidence
A visibility report at an airport or sheltered coast is not a measurement along your entire sea track. Record its location, time and exposure, then compare with the marine forecast and observations from the vessel. Separately assess whether the crew can use the fitted equipment and maintain the required lookout; a weather app cannot perform that assessment.
Make the arrival decision early
Write down what information is needed before committing to a constrained entrance, and where the decision can still be revised. Do not let a fixed booking time turn an uncertain approach into the default choice. The appropriate action depends on the actual position and conditions; this page does not prescribe collision-avoidance manoeuvres or replace applicable navigation rules.
- RYA: passage planning — Passage preparation and route, vessel and crew context.
Editorial review of this material: 27 September 2026. This date concerns the page content; check current forecast issue times and validity at the original sources.