The phenomenon of dead water: why the ships of Cleopatra died
(ORDO NEWS) — The previously unexplainable braking and shaking of fully operational ships in the so-called dead water, finally received a scientific explanation.
When the ship falls into dead water, the journey pauses. In the best case, a ship with fully operational engines will slow down, at worst it will stop. A fair wind can help sailors, but even with full sails, the ship will move slower than it should.
For the first time the phenomenon of dead water was noticed by the Norwegian researcher Fridtjof Nansen in 1983. Going to the north of Siberia, the traveler ended up in a zone where his ship slowed down so much that it became difficult to control. Nansen did not soon pick up the desired speed, and did not understand what had happened.
In 1904, the Swedish physicist and oceanographer Vagn Walfrid Ekman described a similar phenomenon. In his laboratory, the scientist performed an experiment with water of various salinity, as in the part of the Arctic Ocean where Nansen had stalled earlier. Ekman discovered that mechanical waves form at the interface. When the bottom of the ship interacts with these waves, they create additional resistance.
After the discovery of Ekman, scientists realized: the phenomenon of dead water is caused by different density of liquid layers. Differences in density may occur due to different salinity or water temperature. But in any case, the captain of the ship has only two options. He can watch with frustration as the ship drags at a constant abnormally low speed, which Nansen once felt; or stand on the captain’s bridge and sway after the ship, experiencing jerky unrest, discovered in the laboratory by Ekman.
Understanding the cause and types of the phenomenon of dead water, scientists did not know the mechanism for capturing ships in wave captivity. Only recently, physicists, experts in fluid mechanics and mathematics from the CNRS Institute of Natural Sciences and the Laboratory of Mathematics and Applied Sciences of the University of Poitiers first described this mysterious phenomenon. The study’s press release is available on the CNRS website.
A team of scientists classified the waves that occur when fluid layers of different densities come in contact with each other, and then simulated the ship’s movement along the previously mathematically described waves. Modeling showed that the effect of dead water occurs when the waves form something like a conveyor belt. On this “tape” the ship barely moves forward or backward, which from the side looks like a slowdown.
The experiment also showed that there are no fundamental differences between the phenomena that Nansen observed in 1983 and Ekman in 1904. Ekman’s oscillations gradually fade, and the ship begins to move slowly and at a constant speed.
The work of scientists immediately gave rise to a new hypothesis according to one of the oldest mysteries of mankind. It is still unknown why, during the Battle of Actium (31 BC), Cleopatra’s powerful ships perished in the collision with the weak fleet of Octavian. If we assume that the bay of Aktiya, where the battle took place, was filled with dead waters, it becomes clear why the power of the ships of Cleopatra did not help the ruler.
Friction is inversely proportional to speed: the more you drag along a resisting surface, the more it resists. This means that the weak ships of Octavian in dead waters could be more maneuverable and faster than the powerful fleet of the Queen of Egypt.
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