Behind the dead-water phenomenon

© Morgane Parisi - www.StudioBrou.com - What makes ships mysteriously slow down or even stop as they travel, even though their engines are working properly? This was first observed in 1893 and was described experimentally in 1904 without all the secrets of this "dead water" being understood. An interdisciplinary team from the CNRS and the University of Poitiers has explained this phenomenon for the first time: the speed changes in ships trapped in dead water are due to waves that act like an undulating conveyor belt on which the boats move back and forth. This work was published in PNAS on July 6, 2020. In 1893, the Norwegian explorer Fridtjof Nansen experienced a strange phenomenon when he was travelling north of Siberia: his ship was slowed by a mysterious force and he could barely manoeuvre, let alone pick up normal speed. In 1904, the Swedish physicist and oceanographer Vagn Walfrid Ekman showed in a laboratory that waves formed under the surface at the interface between the salt water and freshwater layers that form the upper portion of this area of the Arctic Ocean interact with the ship, generating drag. This phenomenon, called dead water, is seen in all seas and oceans where waters of different densities (because of salinity or temperature) mix. It denotes two drag phenomena observed by scientists.