What makes ships mysteriously slow, or even stalled, while their engines are working properly?

"Dead Water" is a phenomenon first observed in 1893 and described empirically in 1904, without understanding all of its secrets.

Recently, a multidisciplinary team from the French National Center for Scientific Research (CNRS) and the University of Poitiers explained this phenomenon for the first time.

The team showed that the changes in velocities of ships trapped in the dead waters are due to the waves that operate like a wavy conveyor belt with which the ships move back and forth.

This work was published in the journal "Proceedings of the National Academy of Sciences" (PNAS) on July 6.

Riddle lasted 127 years

In 1893, the Norwegian explorer Fridtjof Nansen encountered a strange phenomenon while traveling north of Siberia; His ship slowed due to mysterious power, and he could barely maneuver, let alone return to normal speed.

In 1904, the Swedish physicist and oceanographer Vagn Walfrid Ekman demonstrated in the laboratory that the waves that formed beneath the surface at the confluence of salt water and the freshwater layers that make up the upper part of this region in the Arctic Ocean interact with the ship, which creates strength Clouds.

"Dead water" is a phenomenon described by the explorer Frettiov Nansen and attempted to explain it by the physicist Wagen Eckmann (synthesis from Wikipedia)

This phenomenon, which is called "dead water", appears in all seas and oceans where water of different densities is mixed, whether due to the difference in salinity or temperatures.

In fact, the phenomenon refers to two clouds, observed by scientists, and the cause is unknown: The first is the "Nansen Wave-making drag", which causes an abnormally low constant speed.

The second is "Ekman wave-making drag", which is characterized by the oscillation of the speed in the boxed boat.

Wavy conveyor belt

Physicists, fluid mechanics and mathematicians at the Pprime Institute of the French National Center for Scientific Research and the laboratory of mathematics and applications in Poitiers attempted to solve this mystery.

Scientists used a mathematical classification of different internal waves, and analyzed experimental images on a sub-pixel scale first.

This work showed that these differences in velocity are due to the generation of specific waves that act as a wavy conveyor belt on which the ship moves back and forth.

The scientists also reconciled the observations of Nansen and Eckman, as they showed that the Eckman Oscillation System is only a temporary system, and the ship ends up escaping to reach the constant speed of Nansen.

This scientific work is part of an investigation into the defeat of Cleopatra in the Battle of Actium (Wikipedia - drawing by artist Lorenzo Castro)

Cleopatra defeat

It is worth noting that this scientific work is part of a major project investigating the cause of the loss of the large Cleopatra ships during the Battle of Actium in 31 BC, when they encountered the weaker Octavian ships.

The main question of the research was: Can the Bay of Actium, which has all the characteristics of the fjord, besiege the fleet of the Queen of Egypt in the dead waters?

The research has now come out with another hypothesis to explain this resounding defeat, which was in ancient times attributed to "remora" (lollipop fish) stuck to ship hulls, according to legend.