"Dead-water" is a nautical term used to refer to a strange phenomenon when a ship is hard to maneuver and/or is slowed down almost to a standstill, on a fluid apparently at rest. Although already known by seamen, the first person to describe carefully the so-called "dead-water" phenomenon was Fridtjof Nansen, a Norwegian scientist and explorer. He encoutered it during his expedition to reach the North Pole in 1892 . He realized that the effect occured when a layer of fresh water was on top of salt water, without the two layers mixing.
It is V. W. Ekman who did some intensive experimental work on the topic during his PhD Thesis in Sweden in 1904 . He explained that energy from the boat was mainly transmitted to interfacial waves between the two layers. Hence the energy remaining for the motion of the boat is drastically decreased, along with the speed of the boat.
Studying the dead water phenomenon at the Physics Lab of ENS Lyon was motivated by very interesting discussions with Pr. Leo Maas (see reference below) during international conferences. It seems that this very peculiar topic is still quite unknown from most of the scientific community and the public in general. We have decided to present it through simple experiments, first to students via practical sessions in the lab and then by communicating more widely through internet. Our knowledge of the phenomenon was also increased thanks to novel techniques (compared to Ekman work), and we now dedicate our work to research.
We give in the following section a list of recent communications concerning this project.