Rolling coastal fog is an impressive meteorological phenomenon, but generally harmless for sailors. Although it can create tricky situations, particularly due to loss of visibility, modern tools have greatly improved safety in the face of this type of event. However, a good knowledge of this meteorological phenomenon and constant vigilance remain essential for safe navigation.
The mechanism of coastal fog roll formation
Coastal fog rolls form when warm, moist air meets a colder surface of water. This type of condensation is rapid and spectacular, forming a thick, fog-roll-like cloud layer that sometimes stretches for kilometers across the horizon. This phenomenon is more frequent in maritime regions where the temperature difference between air and water is marked, typically near coasts where cold waters meet warmer air masses in summer or autumn.
Rolling coastal fog is all the more impressive because it seems to stand still, like a gigantic opaque curtain blocking visibility. In addition to its striking visual appearance, it can create difficult sailing conditions with visibility reduced to just a few meters.
An anxiety-inducing phenomenon for sailors
Historically, fog has been one of the most feared phenomena for sailors. Before the advent of modern technology, navigators were confronted with these walls of fog without the means to orient themselves precisely. The loss of bearings, the risk of collision with other boats or underwater obstacles, and the danger of drifting off course, made fog a real nightmare for sailors of the time.
Before technological innovations, foghorns were the main tool for signalling the presence of boats and avoiding accidents. These powerful instruments emitted long, low tones that carried through the fog, enabling sailors to locate other boats or signal their position.
The foghorn, an indispensable tool
In today's foggy conditions, navigation lights are not visible, and one of the main means of signalling yourself to other boats and informing them of your maneuvers is the foghorn. Its use must comply with the RIPAM (Règlement International pour Prévenir les Abordages en Mer - International Regulations for Preventing Collisions at Sea) rules, which set out the behavior to adopt to avoid collisions.
RIPAM specifies that:
-
A mechanically propelled ship making headway must make a prolonged sound at intervals not exceeding two minutes.
-
A ship which is not in control of its maneuvering, a ship with restricted maneuvering ability, a ship handicapped by its draught, a sailing ship, a ship engaged in fishing and a ship towing or pushing another shall, instead of the signals prescribed above, emit three consecutive sounds: one prolonged sound followed by two short sounds, at intervals not exceeding two minutes.
The foghorn also provides information on your specific manoeuvres:
-
One shot: ''I'm changing my course to starboard
-
Two strokes: ''I'm changing my course to port''
-
Three blows: ''I'm going backwards
-
Five strokes minimum: ''I don't understand your intentions
Modern technology for safety
Today, modern equipment such as radars, GPS systems, AIS and depth sounders make it possible to locate obstacles and other boats through fog. Radar, in particular, is one of the most widely used tools, as it is capable of detecting objects at a distance, even in conditions of zero visibility.
Electronic navigation systems, coupled with digital nautical charts, also enable precise tracking, detect temperature variations and pinpoint areas where fog is likely to form. This greatly reduces the risks associated with this type of phenomenon, and enables navigators to react quickly to avoid any incident.
A preventive approach: the importance of observation
1. Keep an eye on temperature differences
One of the first keys to anticipating the appearance of coastal fog on rollers is to pay attention to temperature variations between air and water. In summer, for example, a sea that is still cold in the morning, combined with warm, humid air, is an ideal configuration for the formation of this type of fog. The air temperature can quickly exceed that of the water, resulting in rapid condensation and the formation of a fog roll.
2. Follow local weather patterns
Local and regional weather forecasts, particularly those based on satellite and surface data, are preferred tools. In coastal areas, some sites provide information on sea surface temperature, humidity and pressure variations, which can indicate conditions favorable to fog formation.
3. Frequent training zones
The places most likely to see coastal fog roll in are generally those where cold water meets warm, humid air masses. For example, in the English Channel between France and the UK, this phenomenon is quite common in autumn, when the sea is still cold and the air warmer. The areas around the Gulf of St. Lawrence in Canada, and the coasts of Maine and New England in the USA, also regularly experience episodes of coastal fog.
4. Observe the first signs
Experienced sailors know that coastal roll fog can form slowly, offering a few clues before it appears. A light mist or cloud formation that seems to be closing in on the surface of the water is an early warning signal. This type of fog often forms in the evening or early morning, when the temperature difference between air and water is greatest.
