BOAT-COMPARATOR Guide

Caught in fog on a boat rental: the right reflexes

Slow down, switch on your lights, make noise, trust the GPS without relying on it alone: what to do when fog rolls in during a rental, and how to anticipate it.

Sea fog is one of the most unsettling situations for a renter: in minutes, the coast vanishes, landmarks fade, and the sound of an unseen engine can come from anywhere. Nothing insurmountable, though, provided you have the right reflexes — and above all anticipate it.

Why fog forms (and where)

Sea fog most often forms when mild, moist air passes over colder water: the vapour condenses at the surface. It's common in spring and early summer on Atlantic and Channel coasts, rarer but possible in the Mediterranean. A reference review by Darko Koračin and Clive Dorman, published in 2014 in Atmospheric Research (see the study on Google Scholar), notes that this "advection" fog can persist for hours and form very quickly whenever the air-sea temperature gap and humidity allow. Hence the importance of reading the marine forecast before setting off: visibility given as "moderate to poor" or "fog banks" is no detail.

The five reflexes when fog rolls in

• Slow down to a speed at which you can stop within the visible distance — the basic rule, and often mistake number one.
• Switch on navigation lights immediately, by day as by night: our guide to navigation lights explains which.
• Make noise: a regular sound signal (foghorn) is required in reduced visibility and signals your presence to others.
• Get everyone into a lifejacket and clear the traffic zone if you're near one — a busy channel is the worst place to linger blind.
• Set a course on the GPS and hold it, without sailing "by feel": in fog, your sense of direction lies.

GPS yes, but not alone

An app or chartplotter fixes your position precisely and lets you hold a course or return along a recorded track — a real asset. But it doesn't "see" other boats: that's where an AIS transponder, when the boat has one, makes the difference by showing nearby vessels. Failing that, redouble your listening and sound signals. Keep a backup means in mind too: an electronics failure in fog must not leave you blind.

Anticipate rather than endure

The best way to handle fog is not to be caught in it: with visibility under threat, stay close to the coast, cut the trip short, note the return course before leaving. And if the operator advises against going out, listen — it's the same common sense as facing a gale or thunderstorm. Sailing another day always costs less than a blind return.

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