In the wide expanse of ocean are dying every year, thousands of large and small vessels, especially in wartime. The most valuable and available from sunken ships were retrieved from the seabed. Soviet engineers and divers that are included with the EPRON (i.e., "Expedition underwater works for special purposes"), famous in the world for a successful ascent of more than 150 large vessels. Among them one of the most large - icebreaker Sadko, sunken on the White sea in 1916 because of the negligence of the captain. After lying on the seabed 17 years, this excellent icebreaker was raised by the workers EPRON and entered again into operation.
Lifting technique was entirely based on the application of the law of Archimedes. Under the hull of a sunken ship in the soil of the seabed divers dug 12 tunnels and extended through each of them durable steel towel. The ends of the towels were attached to the pontoons, deliberately being flushed by icebreaker. All this work was made at a depth of 25 m below sea level.
Pontoons served impermeable hollow iron cylinder 11 m long and 5.5 m in diameter. Empty pontoon weighed 50 tons. According to the rules of geometry it is easy to calculate its volume: about 250 cubic meters. It is clear that the empty cylinder should float on water: he displaces 250 tons of water itself weighs only 50; its capacity is equal to the difference between 250 and 50, i.e., 200 tons. To make the pontoon sink to the bottom, fill it with water.
The lifting scheme "Sadko"; shows a section of the icebreaker, pontoons and slings.
When the ends of the steel slings were firmly attached to the sunken pontoons, steel cylinders with hoses to pump compressed air. At a depth of 25 m water pressure to force 25/10 + 1, i.e. 3.5 atmosphere. Air was supplied into the cylinders under a pressure of about 4 atmospheres and, therefore, was to displace water from the pontoons. Lightweight cylinders with great power would come of the surrounding water on the surface of the sea. They floated in the water like a balloon in the air. Joint lifting their strength in the complete displacement of water would be equal to 200 x 12, i.e., 2400 tons. This exceeds the weight of the sunken "Sadko", so for a more smooth lifting pontoons were released from the water only partially.
However, the rise was carried out only after several unsuccessful attempts. "Four of the accident suffered on it the rescue party, while a success, writes in charge of the work the main naval engineer EPRON T. I. Bobryk village in the book "Conquest of the deep". Three times, tensely waiting for the ship, we saw instead of rising icebreaker spontaneously breaking up in the chaos of the waves and foam, pontoons and torn, snakes coiling hoses. Twice appeared and again disappeared in the depths of the sea icebreaker before surfaced and permanently maintained on the surface".