What is the principle behind the phenomenon of mysterious forces that can slow down ships and “dead water”?

In 1893, the Norwegian explorer Fridtjof Nansen was sailing in northern Siberia when he encountered a strange phenomenon: mysterious forces slowed his ship down, were almost inoperable, and it was difficult to return to normal speed. In 1904, Swedish physicist and oceanographer Vagn Walfrid Ekman discovered in a laboratory that waves formed by the interaction between seawater and the ship at the junction of seawater could create resistance to the ship’s travel.

This phenomenon is called dead water and can be seen at the junction of seawater at different densities (due to salinity or temperature).

The scientists observed two resistance phenomena, one of which was The Nansen wave resistance, which caused a persistent abnormally low speed, and the Ekman boom resistance, characterized by the speed oscillation of the trapped vessel for unknown reasons.

Now, researchers at the CnRS and Poitiers University, published in the pNAS journal, explain for the first time how waves encountered in a ship trapped in dead water are like conveyor belts, causing their movementbacks.