Dead water
Dead water is the nautical term for a phenomenon which can occur when a layer of fresh or brackish water rests on top of denser salt water, without the two layers mixing. A ship powered by direct thrust under the waterline (such as a propeller), traveling in such conditions may be hard to maneuver or can even slow down almost to a standstill. Much of the energy from the ship's propeller only results in waves and turbulence between the two layers of water, leaving a ship capable of traveling at perhaps as little as 20% of its normal speed.
The phenomenon was first described by Fridtjof Nansen, the Norwegian Arctic explorer. Nansen wrote the following from his ship Fram in August 1893 in the Nordenskiöld Archipelago near the Taymyr Peninsula:
- "When caught in dead water Fram appeared to be held back, as if by some mysterious force, and she did not always answer the helm. In calm weather, with a light cargo, Fram was capable of 6 to 7 knots.[1] When in dead water she was unable to make 1.5 knots.[2] We made loops in our course, turned sometimes right around, tried all sorts of antics to get clear of it, but to very little purpose."[3]
This phenomenon is observable where glacier runoff flows into salt water without much mixing, such as in fjords.
See also
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References
- ↑ 6 to 7 knots (11.1 to 13.0 km/h; 6.9 to 8.1 mph)
- ↑ 1.5 knots (2.8 km/h; 1.7 mph)
- ↑ Walker, J.M.; "Farthest North, Dead Water and the Ekman Spiral," Weather, 46:158, 1991
External links
- Short movie demonstrating the phenomenon with a model
- Description of Dead Water
- Explanation of dead water
- New Scientist article
- 'dead water' Encyclopædia Britannica Online. 3 December 2009