Maelstroms, often exaggerated by legends, embody the raw forces of the ocean. Although their existence is based on mechanisms that are well understood by science, their impact remains a cause for concern for sailors, whether yachtsmen or professionals. Understanding these phenomena and knowing how to prepare for them is essential for safe sailing.
The maelstrom phenomenon: a dance of oceanic forces
The term maelstrom derived from the Dutch "malen" (turn) and "stroom" (current), conjures up images of devastating whirlpools nourished by folk tales and marine legends. However, these vortices are complex physical manifestations formed by the combination of several geophysical factors:
- Tidal currents
Maelstroms often appear in narrow straits or passages where large masses of water must move between two basins on rising and falling tides. - Bathymetry
Underwater topography plays a key role. Reliefs such as reefs, underwater peaks or chasms create sudden variations in current pressure and speed. These structures can also trigger violent upwellings of water at the surface. - Wind and tide combined
Maelstroms can be amplified when winds are added to tides, increasing the speed and intensity of eddies. These conditions generate irregular waves, making them even more dangerous. - Interactions between opposing currents
In some cases, eddies form in the open sea, where opposing ocean currents collide.
In the northern hemisphere, vortices tend to rotate counter-clockwise, a consequence of the Coriolis force.
How to anticipate and navigate safely?
Sailing in these waters requires rigorous preparation. Charts, weather forecasts and tide calendars must be studied in detail beforehand. Knowledge of neap tide periods, when currents are less intense, is important to minimize risks, as rising and falling tides amplify their intensity, making certain passages impassable at high tide.
Misjudging conditions can disorientate and even trap small boats, which can tip over or be thrown onto nearby reefs. Larger boats, though less vulnerable to direct suction, are subject to forces that make maneuvering difficult, especially in low-visibility conditions.
To cope with such situations, it's crucial to have specialized equipment. The use of GPS and electronic chartplotters can help bypass particularly risky areas, providing precise real-time mapping of currents and obstacles. In addition, sufficiently powerful engines are essential to counter the strong currents that can slow or steer a boat unpredictably.
Swept to -262 m and dragged to the bottom...
If a crew member falls into a maelstrom, the priority is to maintain visual contact. Another priority is to make sure he or she can hold on to a floating object connected to the boat to prevent being swept away by the powerful currents. The use of a safety line is essential when passing through these dangerous zones.
An experiment carried out by Scottish company Northlight Productions highlighted the brutal force of this natural phenomenon and visualized its effects on a floating object. A dummy, equipped with a lifejacket and depth sounder, was thrown into the eddies of the famous Corryvreckan, located between the Scottish islands of Jura and Scarba, one of the world's most powerful whirlpools. After being sucked into the vortex, the dummy was found several kilometers downstream. The probe recorded an immersion to a depth of 262 metres, and the marks visible on the dummy revealed that it had been dragged along the seabed over a long distance.
Not so mysterious phenomena
If historically these nautical phenomena were perceived as fearsome mysteries fuelling dramatic tales such as A descent into the Maelstrom of Edgar Allan Poe, today, thanks to advances in hydrodynamic modeling and in-depth scientific studies, these phenomena are better understood and less frightening.
Researchers can now predict their appearance with precision, enabling a safer approach. Some local agencies even offer supervised excursions with boats specially designed to observe these eddies.
