Friday 18 July 2008

Water and senses


Standing waves

are formed when the level of the water rises at one coast and in the same time drops at the other. A sudden decrease of atmospheric pressure at one of the coasts, appearance of strong wind or heavy rain can all be the causes for standing waves. The fluctuation of the sea level may reach 80cm, which is dangerous for vessels at the harbors.
Seismic waves are formed because of underwater earthquakes. A vessel that is nest the site of the earthquake experiences a hydraulic blow which is why old maps frequently contain non-existent reefs. Seismic waves are often present in the Hawaii region where they have the special name zunami. Such waves are formed in the Pacific Ocean, the Mediterranean, the Caribbean Sea, and the Malaya Archipelago as well. Sometimes, these waves reach the height of 35m and are dangerous not only for the ships but also for the native population because of their destructive power.
Waves change their form
when they reach shallow regions. When the depth becomes equal to the height of the wave, the water particles no longer move in a circle: their orbit becomes elliptical. The length of the waves decreases and the height increases. The front slope of the wave becomes vertical, the top is inclined forward, then it falls and eventually destroys the wave. This phenomenon is called a surf. Its force may reach up to 38 tonnes/m2.
Difficulties The change of water density, resulting from changes of temperature, salinity, and pressure has no practical importance to diving. Even though, water is a dense medium and creates significant difficulties for a diver’s movements. He or she cannot walk or turn as fast as in the air. While working under water, divers must choose positions and movements that create least resistance, e.g. walking sidewards being slightly bent forward. The use of tools is also hindered. For example, the use of a hammer is much more difficult under water than it is in the air. As a result, divers quickly get tired. That is why the work that is to be performed under water should be organized so as to facilitate the diver by minimizing unnecessary movements and providing possible help from the surface. Rapid currents additionally impede the accomplishment of underwater work. Mire, too, can create considerable difficulties for divers. Even the execution of simplest types of work becomes complicated and requires dexterity, resistance, and fitness. That is why rigorous physical preparation is crucial

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